ادوات المعامل lab glassware

كل ما يخص المعامل 

1- ادوات معمليه 

2- زجاجيات 

3- بلاستيكات 

4- سرنجات طبيه زجاج وبلاستيك

5- كيمياويات المعامل 

6- تصنيع زجاجيات

7-  للمبات الاشعه الفوق بنفسجيه والضوء المرئي للاستخدام فى تفاعلات الكيمائ الضوئيه 

التلوث المائى - Aquatic pollution

مقدمة 

الماء مثل الهواء يعتبر أحد المكونات الضرورية للحياة على الكرة الأرضية فهو ضروري للإنسان والحيوان والنبات على حد سواء، ويشكل الماء ما يقارب 80% من مساحة الكرة الأرضية وهو المكون الأساسي للكائنات الحية وقد وصفه سبحانه وتعالى حيث قال : } وجعلنا من الماء كل شيء حي {.

تتنفس الكائنات البحرية الحية الأكسجين الذائب في الماء، لذلك فإنه لابد من المحافظة على تركيزه في الماء. ويتم ذلك عن طريق المحافظة على عدم تلوث مياه المسطحات المائية سواءً مياه الأنهار أو البحيرات أو البحار أو المحيطات لما للملوثات سواء الكيميائية أو الكائنات الحية الدقيقة من أثر فعال في تقليل كمية الأكسجين في هذه المسطحات المائية مما يهدد الحياة البحرية لذلك كان لابد من الاهتمام بدراسة مصادر تلوث المسطحات المائية وطرق مكافحته.

والتلوث من أهم المشكلات والمعوقات التي تواجه الكائنات الحية وفي مقدمتها الإنسان، وغالباً ما يحدث التلوث عن طريق الإنسان ذاته، كيف لا ؟ والإنسان هو السبب المباشر في الدخان والغازات التي تطلقها المصانع إلى الهواء الجوي، وهو الذي يقوم برمي نفايات المصانع والمعامل التي يستخدمها للشرب. لذلك فإن الإنسان يهدد حياته وحياة الكائنات الحية التي تعيش معه في نفس البيئة، فيجب على الإنسان أن يتنبه إلى أنه بسبب هذه الملوثات التي يطلقها ولا يلقي لها بالاً قد يتسبب في حدوث كوارث له أو للكائنات الحية من حوله – لا سمح الله – فمما سبق يمكن أن نستشف تعريفاً عاماً للتلوث على أنه (عبارة عن دخول كميات كبيرة من عناصر غريبة للبيئة المحلية).

والتلوث كلمة جامعة لأنواع عدة (أنواع التلوث) ولكننا في هذا البحث سوف نقتصر على نوع واحد فقط، ألا وهو التلوث المائي، حيث هو من الأهمية بمكان فإن الماء هو سر الحياة وصدق الله حينما قال في محكم التنزيل : } وجعلنا من الماء كل شيء حي {.

وسوف نطرق هذا الموضوع في بضع صفحات سائلاً المولى عز وجل أن ينفع بهذا البحث كاتبه وقارئه وأن ينال استحسان الجميع وعلى الله وحده اعتمادي وإليه وجهتي واستنادي.

التلوث المائي

تلوث الماء ( هو كل تغير في الصفات الطبيعية والكيماوية، والبيولوجية للماء، مما يجعله عائقاً للاستخدامات المشروعة منه).

وعندما يطلق تلوث الماء يجب التنبه إلى أن الماء لا يمكن أن يكون في صورة نقية تماماً، لكن المقصود من تلوث الماء مدى خطورته على الغرض من استخدامه، فالماء الذي يستخدم للشرب قد يعتبر ملوثاً لكنه عند استخدامه للأغراض الأخرى كالمصانع فنعتبره غير ملوث، كذلك الماء الصالح للشرب يعتبر ملوثاً عند استخدامه لبعض الصناعات الكهربائية إذاً فمفهوم تلوث الماء مفهوم نسبي يخلف باختلاف الاستخدامات المناطة منه.

مصادر تلوث الماء :

لعل أهم مصادر تلوث الماء هو تدفق مياه المجاري والمخلفات والمياه الصناعية والبترول إلى المسطحات المائية كما أن المبيدات الكيميائية ونفايات المصانع وملوثات الهواء تصل إلى المسطحات المائية عن طريق مياه الأمطار أو الرياح عند ملامستها لسطح الماء. ولعل القاسم المشترك بين هذه الملوثات هو تأثيرها على تركيز الأكسجين في الماء ويتم ذلك عن طريق نمو الكائنات المائية الدقيقة مثل البكتريا في المياه الملوثة بمياه المجاري حيث تستهلك هذه الكائنات الأكسجين المذاب في الماء لتكسير المواد الكيميائية العضوية الملوثة للماء مما يؤثر على تركيز الأكسجين في الماء ويهدد الحياة البحرية. كما أن الملوثات الكيميائية السامة مثل العناصر الثقيلة والمبيدات وغيرها تصل إلى الكائنات الحية مثل الأسماك والنبات مما يؤثر على نموها وتكاثرها وكذلك تؤثر على الإنسان المستهلك النهائي لهذه الكائنات، هذا بالإضافة إلى الأخطار المباشرة على الإنسان من تعرض مياه الشرب للتلوث سواء بالكائنات الحية الدقيقة أو بالكيميائيات السامة.

وفيما يلي أهم مصادر تلوث المياه :

1 – البترول (النفط) :

مع زيادة إنتاج البترول وتصديره فإن المسطحات المائية التي تمر من خلالها ناقلات البترول تؤدي إلى تلوثها إما عن طريق الحوادث التي تتعرض لها تلك الناقلات مما يؤدي إلى تسرب البترول أو إلى إلقاء الماء الموجود في مستودعات الاستقرار للناقلات والذي يحمل كميات من البترول. وبذلك تعتبر ناقلات البترول من أخطر مسببات تلوث البحار والمحيطات حيث أنه بعد إفراغ حمولتها من البترول ومنتجاته فإنها تملأ خزاناتها بماء البحر لتستعمله كثقل لحفظ توازنها، وعند مغادرتها الميناء، تفرغ حمولتها من هذا الماء الملوث بالبترول في البحر، وتدل الدراسات على أن ناقلات البترول تلقي بحوالي 1% من حمولتها من البترول ومنتجاته في البحر. وبذلك فإن ما يلقى في البحار يومياً يقارب عشرين ألف طن من البترول ومنتجاته، بالإضافة إلى ذلك فإن مصافي البترول تلقي المياه المستهلكة في عمليات التكرير في المسطحات المائية، كما أن التنقيب وإنتاج البترول في عرض البحر يعتبر أحد مصادر التلوث، كما حدث من تسرب البترول من آبار النوروز التي سببت بقع زيت كبيرة في مياه الخليج العربي عام 1403هـ وذلك أثناء الحرب العراقية الإيرانية.

يشكل البترول المتسرب إلى المسطحات المائية طبقة رقيقة. حيث تدل الدراسات بأن الطن الواحد من البترول يغطي مساحة قدرها 12 كيلو متر مربع، وهذا يؤدي إلى تسمم بعض الطيور البحرية مباشرة، كما تتعرض الكائنات البحرية الأخرى إلى أخطار جسيمة سببها قلة تركيز الأكسجين في الماء. حيث أن هذه الطبقة البترولية تمنع الأكسجين الجوي من الوصول إلى الماء، مما يقلل نسبة الأكسجين في الماء، كما أن جزءاً من الأكسجين، المذاب فيه يستهلك في أكسدة هذه الطبقة البترولية، وهذا يؤثر على الحياة البحرية.

2 – مياه المجاري :

إن قذف مياه المجاري في المسطحات المائية يعتبر ولا شك من أكبر مصادر تلوث الماء وذلك لما تحمله هذه المياه من مواد عضوية تساعد على نمو الكائنات الحية الدقيقة مثل البكتريا المسببة للأمراض، كما أن وجود هذه المواد العضوية يستهلك جزءاً من الأكسجين المذاب في الماء عن طريق أكسدة هذه المواد في وجود البكتريا التي تساعد على حدوث الأكسدة. وهذا يؤثر على الكائنات المائية الحية من أسماك ونبات، ومن المعروف أن الحد الأدنى لبقاء الكائنات المائية حية إذا كان الماء يحتوي على 3 إلى 4 أجزاء في المليون من الأكسجين المذاب، لذلك إذا استطعنا أن نحافظ على هذه النسبة من الأكسجين فإنه لا خوف من تلوث الماء. الجدير بالذكر أن المسطحات المائية تستطيع تعويض الأكسجين من الغلاف الجوي، بفعل الرياح والأمواج، ولكن إذا كان وصول مياه المجاري إلى المسطحات المائية يفوق قدرة الماء على الحصول على الأكسجين فإنه يحــدث نقص في تركيز الأكسجين ومن ثم حــدوث التلوث وتعرض الكائنات المائية الحية للخطر.

وحيث أن الكائنات المائية الدقيقة مثل البكتريا المؤكسدة تستخدم الأكسجين المذاب في الماء لتكسير المواد العضوية وتحليلها، فإنه إذا قلت كمية الأكسجين المذاب في الماء إلى درجة كبيرة يؤدي إلى ضعف الكائنات الدقيقة المسئولة عن تحلل المواد العضوية الموجودة في مياه المجاري مما يؤدي إلى فقد قدرتها على التكسير السليم مما يؤدي إلى تكسير هذه المواد إلى نواتج ضارة وبالتالي يتعفن الماء وينبعث منه روائح كريهة تشتمل على غاز كبريتيد الهيدروجين.

بالإضافة إلى ذلك فإن مياه المجاري تحتوي على كثير من المخلفات الكيميائية مثل المنظفات والصابون وغيرها، وقد اتضح أن بعض المنظفات يحدث رغاوي في مياه المجاري والأنهار يصعب تحللها بيولوجياً الأمر الذي يؤدي إلى تلوث المسطحات المائية بشكل واضح بالإضافة إلى ذلك فهي سامة للكائنات البحرية الحية.

هذا ويجري الاتجاه حالياً للتخلص من مشكلة مياه المجاري نهائياً وذلك بتنقيتها ومعالجتها مما يؤدي إلى الاستفادة من مياهها المعالجة في ري المزارع وكذلك يستفاد من السماد المتخلف أيضاً في الزراعة.

3 – المبيدات :

للمبيدات أهمية كبيرة في زيادة كفاءة الإنتاج الزراعي وتتمثل في القضاء على الحشرات والفطريات والأعشاب الضارة، كما أن لهذه المبيدات آثاراً سيئة على تلوث البيئة سواء الهواء أو الماء. فبعد رش النباتات بهذه المبيدات فإنها تصل إلى المسطحات المائية عن طريق مياه الأمطار ومجاري الصرف، بالإضافة إلى ذلك فإن هذه المبيدات وخاصة المبيدات الحشرية تصل إلى المسطحات المائية مباشرة عند رش البحيرات أو الأنهار للقضاء على الحشرات، كما تصل إلى المسطحات المائية عن طريق الأمطار أو الرياح بعد رش الهواء للقضاء على الحشرات.

عند وصول هذه المبيدات إلى المسطحات المائية فإن ذلك يؤثر على الكائنات البحرية الحية سواءً الحيوانية أو النباتية كما يؤثر على الطيور المائية، وقد أثبتت الدراسات وجود هذه المبيدات في خلايا الكائنات البحرية الحية مما يؤدي في بعض الأحيان إلى موت هذه الكائنات. ولقد امتد أثرها إلى الإنسان الذي يتناول هذه الكائنات وخاصة الأسماك، كما أن هذه المبيدات قد تسبب ضرراً مباشراً للإنسان من جراء تناول المواد الغذائية (النباتات) التي رشت بهذه المبيدات.

4 – الأمطار الحمضية :

إن المكونين الرئيسيين للأمطار الحمضية هما حمض الكبريتيك وحمض النيتريك وهما يتكونان من أكاسيد الكبريت وأكاسيد النيتروجين في وجود الماء، وتتكون هذه الأكاسيد على شكل غازات تصدر من المخلفات الصناعية ومن احتراق الوقود احتراقاً غير كامل كما يحدث في عوادم السيارات والمصانع ومحطات الكهرباء.

هذا وقد تسبب الأمطار الحمضية تغير الرقم الهيدروجيني _ph (يعبر عن تركيز البروتون أو الحمض) في المسطحات المائية مما يؤثر على الكائنات المائية الحية حيث يؤدي في بعض الأحيان إلى موت هذه الكائنــات، إضافـة إلى الأضـرار التي تسببها الأمطـار الحمضـية على النبــاتات البــرية وفي تآكل مـواد البناء والمعادن.

5 - المياه الصناعية :

يقصد بالمياه الصناعية، المياه التي تستخدم للتبريد في المصانع ومحطات توليد الطاقة الكهربية والمحطات النووية، ولا شك بأن تسرب مياه مرتفعة الحرارة إلى الأنهار أو البحار سوف يؤثر على الكائنات البحرية الحية وذلك لأن الماء الساخن يحتوي على كمية أقل من الأكسجين، كما أن ارتفاع درجة حرارة الماء يؤثر تأثيراً مباشراً على الكائنات البحرية حيث أن بعضها لا يلائمها المياه الدافئة. هذا بالإضافة إلى ما قد تحتويه المياه الصناعية من مواد كيمائية كمخلفات صناعية ملوثة للبيئة. لذلك فلابد من تحويل المياه الصناعية إلى حلقات مغلقة لا تصب في المسطحات المائية وتلوثها.

6 – المعادن الثقيلة :

تصل مركبات المعادن الثقيلة إلى المسطحات المائية عن طريق المبيدات المحتوية على المعادن الثقيلة وكذلك عن طريق المخلفات الصناعية ومخلفات الوقود الناتجة من المصانع أو وسائل النقل، بالإضافة إلى ما يصل إلى المسطحات المائية من معادن ثقيلة مصدرها طبيعي وذلك من البراكين، كما أن الصخور والتربة يحتويان على أملاح المعادن الثقيلة، وعند تعرضها للظروف الجوية المختلفة ونزول المطر فإن كاتيونات هذه المعادن تتحرر وتلوث المسطحات المائية، ومن أخطر مركبات المعادن الثقيلة والتي تنتشر بشكل واسع هي كل من مركبات الزئبق والرصاص والكادميوم والنحاس والكروم والكوبلت والنيكل والزنك والزرنيخ والبيريليوم.

وتختلف العناصر الثقيلة عن غيرها من الملوثات بأن معظمها له الصفة التراكمية. حيث يتراكم في أجسام الحيوانات المائية مثل الأسماك والطيور المائية وفي أجزاء النباتات المختلفة حتى يصل إلى تراكيز عالية، عندها تبدأ آثار التسمم بالمعادن الثقيلة في الظهور مما يهدد بقاء هذه الكائنات، كما أن مركبات هذه المعادن الثقيلة تصل إلى الإنسان عن طريق تناوله الأسماك التي تحتوي خلاياها على مركبات هذه المعادن.

أنواع الملوثات المائية :

هناك ثلاث أنواع من الملوثات المائية هي الملوثات الفيزيائية، الكيميائية، البيولوجية.

1 – الملوثات الفيزيائية (الطبيعية) : هي كل ما يضاف إلى الماء من الطبيعة ويمكن إزالته بطرق معالجة الصفات الطبيعية للماء المذكورة سابقاً، وتسبب هذه الملوثات في تغيير طعم ولون ورائحة الماء، وتتكون هذه الملوثات من تخلف وترسب المواد العالقة في الماء.

2 – الملوثات الكيميائية : فإما أن تكون عضوية الأصل أو غير عضوية، ومن أمثلة الملوثات غير العضوية : الحديد والمنجنيز والخارصين والنحاس والكالسيوم والمغنسيوم، ويجب أن يكون تركيز هذه المواد عند حد معين يعتمد على حسب نوعية استعمال الماء للأغراض المختلفة، وللملوثات الكيميائية العضوية أنواع مختلفة أهمها الفينولات ومشتقاتها ومخلفات المبيدات الحشرية، والمنظفات الصناعية والمركبات العضوية الأخرى القابلة للتكسر البيولوجي.

3 – الملوثات البيولوجية : وتعتبر البكتيريا والفيروسات وإفرازات الكائنات الدقيقة الحيوانية أو النباتية هي أهم أنواع الملوثات البيولوجية، وتسبب هذه الملوثات الأمراض والتسمم في بعض الأحيان.

مراحل تحلل الملوثات :

عادة ما يمر الملوث في الوسط المائي بثلاث مراحل لتحلله :

أ – منطقة التحلل :

هي المنطقة التي تبدأ فيها عملية التحلل للملوث : حيث تتجمع الملوثات – عادة – في القاع في الطبقة الطينية؛ إذ تترسب المواد الصلبة وتزداد فيها نسبة التعكر وأعداد البكتريا، وتختفي بعض أنوع الفطريات لعدم قدرتها على تحمل الظروف البيئية الجديدة، وقد تنقرض تماماً بعض الكائنات، بينما تسود كائنات أخرى.

وعند فحص قاع المجرى المائي – عند هذه النقطة – تتواجد كثير من الكائنات الحية الكبيرة مثل الديدان الحلقية والاسطوانية، ويرقات الحشرات والأكاروسات، وتنخفض أعداد الطحالب لقلة الضوء، وتنشط أنواع عديدة من الكائنات الحية الصغيرة، مثل البكتريا والبروتوزوا، وخاصة الهدبيات، والخيطيات.

ب – منطقة التحلل النشط :

وفيها تقل درجة التعكر وتزداد أعداد البكتريا بدرجة كبيرة، وكذلك الفطريات، وذلك في الرواسب التي تجمعت في القاع قرب نهاية المنطقة، ونلاحظ زيادة في نشاط الهائمات الحيوانية التي تقوم بالتهام الأوليات النباتية، وتخرج نواتج تحلل هذه الكائنات في صورة نترات وفوسفات، وتظهر أنواع من الطحالب.

جـ – منطقة الانتعاش :

وهي منطقة تالية تتميز باستعادة المجرى المائي لحالته الأولى، من حيث محتواه من الأكسجين وبقية خواصه الطبيعية، وتبدأ الصورة البيولوجية في التحول لصالح النشاط النباتي فيتوفر الضوء، وتزداد أعداد الطحالب، ويبدأ نمو الأعشاب المائية، مثل عدس الماء، والألوديا، والأزولا ورد النيل وغيرها من النباتات التي تنافس الطحالب في كمية الضوء المتاح.

مكافحة تلوث الماء :

1-     التخلص السليم من النفايات الكيميائية وعدم وضعها في مياه المجاري بل يتم التخلص منها بالحرق إذا كانت نواتج الاحتراق غير ضارة أو تحويلها إلى مركبات غير ضارة مثل تحويل الأحماض إلى أملاح وذلك بمعادلتها بالقواعد.

2-     المحافظة على عدم تلوث البحار والأنهار بالبترول والمخلفات الصناعية ومحاولة التخلص من أي تسربات تقع بقدر الإمكان وبأسرع وقت ممكن.

3-     محاولة جمع مياه المجاري وإعادة استخدامها مرة أخرى في ري المزارع والحدائق بعد معالجتها كيميائياً وبيولوجياً كما يتم استخدام الأسمدة الناتجة عن هذه المعالجة في الزراعة.

4-     المحافظة على عدم تلوث الهواء بالمواد الكيميائية حيث أن مياه الأمطار والرياح تحول ملوثات الهواء إلى ملوثات للتربة والمسطحات المائية.

5-          عدم استخدام المبيدات الثابتة وغير القابلة للتفكك مثل د. د. ت. والكيلات الزئبق.

التأثير الصحي للمياه الملوثة :

إن الماء يعمل كناقل فعال للأمراض والطفيليات، حيث تعتمد هذه الكائنات على الماء في حياتها.

يمكن تقسيم الأمراض والطفيليات بالماء كالتالي :

أ / أمراض متولدة من الماء :

هذا النوع من الأمراض تسببه بعض الميكروبات التي تعيش في الماء الملوث ومن أهم هذه الأمراض التيفوئيد والكوليرا.

ب / أمراض ناتجة عن الغسيل بالماء :

أهم هذه الأمراض أمراض الإسهال وأمراض الجلد وأمراض العيون وتنتشر هذه الأمراض في الأماكن التي لا تتوفر بها كمية المياه اللازمة للنظافة الشخصية.

جـ / أمراض مسئول عنها الماء :

وهي الأمراض التي تعتمد على الماء لتكملة دورة حياتها، وأهم الطفيليات التي تسبب هذه الأمراض البلهارسيا ودودة الجوانيا، ودودة الاسكارس والدودة الكبدية وغيرها.

المراجـــــــع

+      تلوث المياه العذبة.

د / أحمد عبد الوهاب عبد الجواد.

+      ملوثات البيئة أضرارها، مصادرها، طرق مكافحتها.

د / محمد الحسن.

د / إبراهيم المعتاز.

+      تلوث المياه العذبة.

د / أحمد عبد الوهاب عبد الجواد.

+      ملوثات البيئة أضرارها، مصادرها، طرق مكافحتها.

د / محمد الحسن.

د / إبراهيم المعتاز.

المصدر 

اعضاء هيئة التدريس قسم الأحياء » فيصل عبدالقادر عبدالوهاب بغدادي » Environment » التلوث المائي »

 بجامعة ام القرى 

كاتب المقدمة :

علي بن حامد العمري

مع اطيب التمنيات بالتوفيق للجميع 

محمد حسان

منح دراسيه يناير 2020 - Scholarships January 2020

 بعض المنح الدراسيه الخاصه بشهر يناير 2020 

1-   

https://www.u-tokyo.ac.jp/en/prospective-students/amgen_program.html?fbclid=IwAR15-0N6ctujkg7Kcjt3zHeWsJ6XLXuskmiMHNmGUsFsGGqoSNhEx48ouj0

2-
https://www.beiersdorf.com/career/students-and-graduates/international-internship-challenge
3-
http://www.mfa.gov.bn/Pages/BDGS.aspx
4-
https://www.facebook.com/Qisaty-%D9%82%D8%B5%D8%AA%D9%8A-107727897407713/
5-
http://www.lse.ac.uk/cities/education/emc/lse-sawiris

بالتوفيق للجميع

Refraction and Reflection of Waves

Refraction and Reflection of Waves

Refraction

Any type of wave can be refracted, which means a change of direction.

Refraction can occur when the speed of a wave changes,
as it moves from one environment to another.

After refraction, the wave has the same frequency but a different speed, wavelength and direction.

When a wave enters a new environment,
its change in speed will also change its wavelength.

If the wave enters the new environment at any angle
other than normal to the boundary,
then the change in the wave's speed will also change its direction.
This is most easily shown with water waves.

Reflection

 .

Any type of wave can be reflected.
We shall look at the reflection of Sound, Water and Light Waves.
Reflection best occurs from flat, hard surfaces.
After reflection, a wave has the same speed, frequency and wavelength,
it is only the direction of the wave that has changed.

For light (and other electromagnetic radiation)
a flat shiny surface, like a plane mirror, is a good reflector.
A plane mirror is one which is straight and not curved.

The light ray which hits the mirror is called the incident ray.
The light ray which bounces off the mirror is called the reflected ray.

The angle of incidence equals the angle of reflection,  i = r.
This means that whatever angle the light ray hits the mirror,
it will be reflected off at the same angle
(like snooker balls bouncing off a cushion).

If the surface of the mirror is not smooth but rough or bumpy,
then light will be reflected at many different angles.
The image in the mirror will be blurred and unclear.
This is called diffuse reflection.

When you look into a mirror,
you see a reflection which is an image of the real object.

The image appears to be the same distance behind the mirror
as the real object is in front of it.
This is because the brain thinks that light travels in straight lines
without changing direction.

The image is called virtual because the light rays (shown as dotted lines)
never really go there.
The virtual image is the same size as the object
but with left and right reversed.

good luck 

mohamed hassaan

Escherichia coli (E. coli

Escherichia coli 

(E. coli)

E. coli bacteria: what are they, where did they come from, and why are some so dangerous?

Escherichia coli (E. coli) are members of a large group of bacterial germs that inhabit the intestinal tract of humans and other warm-blooded animals (mammals, birds). Newborns have a sterile alimentary tract, which within two days becomes colonized with E. coli. 

More than 700 serotypes of E. coli have been identified.  The “O” and “H” antigens on their bodies and flagella distinguish the different E. coli serotypes, respectively.  The E. coli serotypes that are responsible for the numerous reports of outbreaks traced to the consumption of contaminated foods and beverages are those that produce Shiga toxin (Stx), so called because the toxin is virtually identical to that produced by another bacteria known as Shigella dysenteria type 1 (that also causes bloody diarrhea and hemolytic uremic syndrome [HUS] in emerging countries like Bangladesh) (Griffin & Tauxe, 1991, p. 60, 73).  The best-known and most notorious Stx-producing E. coli is E. coli O157:H7.  It is important to remember that most kinds of E. coli bacteria do not cause disease in humans, indeed, some are beneficial, and some cause infections other than gastrointestinal infections, such urinary tract infections.  This section deals specifically with Stx-producing E. coli, including specifically E. coli O157:H7.

Shiga toxin is one of the most potent toxins known to man, so much so that the Centers for Disease Control and Prevention (CDC) lists it as a potential bioterrorist agent (CDC, n.d.).  It seems likely that DNA from Shiga toxin-producing Shigella bacteria was transferred by a bacteriophage (a virus that infects bacteria) to otherwise harmless E. coli bacteria, thereby providing them with the genetic material to produce Shiga toxin. 

Although E. coli O157:H7 is responsible for the majority of human illnesses attributed to E. coli, there are additional Stx-producing E. coli (e.g., E. coli O121:H19) that can also cause hemorrhagic colitis and post-diarrheal hemolytic uremic syndrome (D+HUS).  HUS is a syndrome that is defined by the trilogy of hemolytic anemia (destruction of red blood cells), thrombocytopenia (low platelet count), and acute kidney failure.

Stx-producing E. coli organisms have several characteristics that make them so dangerous.  They are hardy organisms that can survive several weeks on surfaces such as counter tops, and up to a year in some materials like compost.  They have a very low infectious dose meaning that only a relatively small number of bacteria (fewer than 50) are needed “to set-up housekeeping” in a victim’s intestinal tract and cause infection.

The Centers for Disease Control and Prevention (CDC) estimates that every year at least 2000 Americans are hospitalized, and about 60 die as a direct result of E. coli infection and its complications. A recent study estimated the annual cost of E. coli O157:H7 illnesses to be $405 million (in 2003 dollars), which included $370 million for premature deaths, $30 million for medical care, and $5 million for lost productivity (Frenzen, Drake, and Angulo, 2005).

E. coli O157:H7—a foodborne pathogen

E. coli O157:H7 was first recognized as a foodborne pathogen in 1982 during an investigation into an outbreak of hemorrhagic colitis (bloody diarrhea) associated with the consumption of contaminated hamburgers (Riley, et al., 1983).  The following year, Shiga toxin (Stx), produced by the then little-known E. coli O157:H7, was identified as the real culprit. 

In the ten years following the 1982 outbreak, approximately thirty E. coli O157:H7 outbreaks were recorded in the United States (Griffin & Tauxe, 1991). The actual number that occurred is probably much higher because E. coli O157:H7 infections did not become a reportable disease (required to be reported to public health authorities) until 1987 (Keene et al., 1991 p. 60, 73).  As a result, only the most geographically concentrated outbreaks would have garnered enough attention to prompt further investigation (Keene et al., 1991 p. 583).  It is important to note that only about 10 percent of infections occur in outbreaks, the rest are sporadic. 

The CDC has estimated that 85 percent of E. coli O157:H7 infections are foodborne in origin (Mead, et al., 1999).  In fact, consumption of any food or beverage that becomes contaminated by animal (especially cattle) manure can result in contracting the disease.  Foods that have been identified as sources of contamination include ground beef, venison, sausages, dried (non-cooked) salami, unpasteurized milk and cheese, unpasteurized apple juice and cider (Cody, et al., 1999), orange juice, alfalfa and radish sprouts (Breuer, et al., 2001), lettuce, spinach, and water (Friedman, et al., 1999).  Pizza and cookie dough have also been identified as sources of E. coli outbreaks.

Sources of E. coli infection

E. coli O157:H7 bacteria and other pathogenic E. coli is believed to mostly live in the intestines of cattle (Elder, et al., 2000) but has also been found in the intestines of chickens, deer, sheep, and pigs. 

A 2003 study on the prevalence of E. coli O157:H7 in livestock at 29 county and three large state agricultural fairs in the United States found that E. coli O157:H7 could be isolated from 13.8 percent of beef cattle, 5.9 percent of dairy cattle, 3.6 percent of pigs, 5.2 percent of sheep, and 2.8 percent of goats. Over seven percent of pest fly pools also tested positive for E. coli O157:H7 (Keen et al., 2003). 

Shiga toxin (Stx)-producing E. coli does not make the animals that carry it ill. The animals are merely the reservoir for the bacteria.

E. coli can be transmitted from several sources:

Food

Water

Animals

Humans

Foodborne Transmission of Stx-Producing E. coli

E. coli O157:H7 was first recognized as a food borne pathogen in 1982 during an investigation into an outbreak of hemorrhagic colitis (bloody diarrhea) associated with consumption of contaminated hamburgers (Riley, et al., 1983).  The following year, Shiga toxin (Stx), produced by the then little-known E. coli O157:H7, was identified as the real culprit.

Outbreaks

In the ten years following the 1982 outbreak, approximately thirty E. coli O157:H7 outbreaks were recorded in the United States (Griffin & Tauxe, 1991). It is important to note that only about 10 percent of infections occur in outbreaks, the rest are sporadic. 

The actual number is probably much higher because E. coli O157:H7 infections did not become a reportable disease (required to be reported to public health authorities) until 1987 (Keene et al., 1991 p. 60, 73).  As a result, only the most geographically concentrated outbreaks would have garnered enough attention to prompt further investigation (Keene et al., 1991 p. 583).

The CDC has estimated that 83 percent of E. coli O157:H7 infections are foodborne in origin (2009 report). Consumption of any food or beverage that becomes contaminated by animal (especially cattle) manure/feces can result in disease.

Foods that have been identified as sources of contamination include:

• Ground beef
• Venison
• Sausages
• Dried (non-cooked) salami
• Unpasteurized milk and cheese
• Unpasteurized apple juice and cider
• Alfalfa, parsley, and radish sprouts
• Lettuce, cabbage, and spinach
• Fruit, nuts, and berries
• Cookie dough

The Centers for Disease Control and Prevention (CDC), Enteric Disease Branch, released a report dated September 14, 2009 entitled “Update on the Epidemiology of Shiga toxin-producing E. coli (STEC) in the United States”.  The contents of this timely report have been incorporated into this Web piece.  CDC’s estimates of the annual number of illnesses caused by Stx-producing E. coli (both O157:H7 and non O157:H7) are as follows:

E. coli O157

• 73,000 illnesses
• 2200 hospitalizations
• 61 deaths

Non-O157 STEC

• 36,700 illnesses
• 1100 hospitalizations
• 30 deaths

E. coli infections continue to largely be a foodborne illness. 

For the period of 1998-2007 during which there were 334 outbreaks (7864 illnesses), the vehicles for the infections were as follows:

E. coli O157:H7

• Foodborne: 69%
• Waterborne: 18%
• Animals or their environment: 8%
• Person-to-person: 6%

Non-O157:H7

• Foodborne:  83%
• Waterborne:  9%
• Animals or their environment:  5%
• Person-to-person:  4%

According to the cited recent CDC report, the mode (kind of food) causing illness secondary to E. coli O157:H7 outbreaks have changed in the past several years.  (Note the emergence of leafy vegetables).

E. coli O157:H7

                                                                                       

	(1998-2002)	(2003-2007)
Beef	33	42
Leafy vegetable	11	41
Dairy	13	13
Fruits-nuts	41	2
Sprouts	1	2
Wild Game	0	1
Poultry	2	0

Non-E. coli O157:H7

                                             

	(1990-2007)
Fruit (nuts, apple juice and cider, berries)	3
Dairy (cheese, margarine)	2
Leafy vegetables	1
Beef	0

The Role of Toxin Receptors

Cattle and other animals are merely reservoirs for E. coli bacteria.  Shiga toxin (Stx)-producing E. coli do not make the animals carriers ill because their bodies do not have receptors for the toxin.  Receptors are tiny protein structures that are located on the surface of cells, and are specific for a particular antigen (substance), in this case, Shiga toxin.  They provide a “docking station” for the toxin, without which it cannot injure animals or their organs (e.g., kidneys). 

E. coli in Ground Beef

At one time, prior to the widespread dissemination of E. coli throughout the food chain, hemolytic uremic syndrome (HUS) secondary to E. coli O157:H7 infection was known as “Hamburger Disease”.  The ground beef connection has not gone away.  Numerous outbreaks and massive recalls of contaminated ground beef continue to plague both the industry and the public. 

Meat typically becomes contaminated with E. coli during the slaughtering process, when the contents of an animal’s intestines and feces are allowed to come into contact with the carcass.  Unless the carcass is properly sanitized, E. coli bacteria are mixed into the meat as it is ground.

Because E. coli are mixed throughout the meat during the grinding process, and is not just on the surface, ground beef must be cooked throughout to a temperature of 165 degrees Fahrenheit since only thorough cooking will kill them (See E. coli prevention).

The fall of 2007 was a dreadful season.  The Food Safety and Inspection Service (FSIS) of the US Department of Agriculture (USDA) announced the recall of nearly 30 million pounds of ground beef in 20 separate recalls for E. coli contamination in 2007.  Many of the recalls were announced after illness had been traced to the specific contaminated products. 

One of Several September 2007 Ground Beef E. coli Outbreaks

On September 29, 2007, the USDA and FSIS announced that 21.7 million pounds of frozen ground beef patties were being recalled for possible E. coli O157:H7 contamination. 

The announcement came after health officials in several states, who were investigating reports of E. coli O157 illnesses, found that many ill persons had consumed the same brand of frozen ground beef patties.

State public health departments and federal laboratories tested patties recovered from patients’ homes; tests were conducted by the New York State Wadsworth Center Laboratory and by a FSIS laboratory on opened and unopened packages of the same brand of frozen ground beef patties.  They yielded E. coli O157 isolates with several different “DNA fingerprint” patterns, as determined through Pulsed Field Gel Electrophoresis (PFGE). 

An October 9, 2007 CDC news release stated that “several state health departments, CDC, and the USDA-FSIS were investigating a multi-state outbreak of Escherichia coli O157:H7 infections” (CDC, October 9, 2007).

Investigators compared the “DNA fingerprint” patterns of E. coli isolated from 35 ill individuals to E. coli strains isolated from the recalled ground beef patties and found that the strain isolated from the ill people matched at least one of the DNA patterns of E. coli strains found in the frozen ground beef patties. 

Three cases had confirmed associations with recalled products because the E. coli strain isolated from their stool was also isolated from meat in their home.

The ill persons, ages one to 77 years, resided in eight states: Connecticut (2), Florida (1), Indiana (1), Maine (1), New Jersey (8), New York (11), Ohio (1), and Pennsylvania (10).

E. coli in Fresh Fruits and Vegetables

Fruit that comes in contact with animal, especially cattle, feces, (as might happen if fruit has fallen and is harvested/picked from/off the ground), can also transmit Stx-producing E. coli.

A specific example is the November 1996 unpasteurized apple juice outbreak:

• On November 1, 1996, Odwalla Company recalled all of its products containing unpasteurized apple juice after several children developed Hemolytic Uremic Syndrome (HUS) Add link to about-hus.com.
• The public health agencies that conducted an investigation into the Odwalla apple juice E. coli outbreak concluded that contamination occurred when “dropped” apples were harvested from ground that had been contaminated by cow manure; it is important to know that E. coli O157:H7 can survive for long periods of time (e.g., > 1 yr [in compost], for example).
• This tragedy led to the dramatic implementation of juice pasteurization

Fresh vegetables can become contaminated pre- or post-harvest.  Contaminated seeds, irrigation water, and flooding have contributed to E. coli outbreaks traced to sprouts, lettuce, spinach, parsley, and other fresh produce.  According to the September 2009 CDC report, there were no leafy green vegetables implicated in any E coli O157:H7 outbreaks prior to 1995, but since then (1995-2005) there have been 27 such outbreaks:

• Lettuce and lettuce salads: 21 outbreaks
• Cabbage: 3 outbreaks
• Parsley: 2 outbreaks
• Spinach: 1 outbreak

June 2006 Lettuce E. coli Outbreak

In early August 2006, public health officials in a mid-sized city in Utah became aware that several people attending a teachers’ conference had contracted E. coli O121:H19 (another Shiga toxin-producing E. coli).  The Weber-Morgan Health Department (HD) issued a news release indicating that three people had contracted E. coli O121:H19 from the same source, and that two had developed HUS.  Several days later, HD officials revised the number of outbreak victims to four, including three who had developed HUS (Weber-Morgan Health Department, 2006, August 7). 

One of the patients with confirmed HUS had not attended the teachers’ conference, but had eaten cheeseburgers with iceberg lettuce prepared at the same restaurant during the outbreak.  The second confirmed HUS case was an attendee of the teachers’ conference.  A third was determined to be a secondary case who acquired E. coli from a person infected at the conference.  Samples from three of the HUS patients with E. coli O121:H19 were laboratory-confirmed as genetic matches through DNA sub-typing using Pulsed Field Gel Electrophoresis (PFGE), confirming that their E. coli infections all came from the same source.

Eventually, HD officials concluded that the source of the E. coli outbreak was iceberg lettuce prepared at the same fast-food facility.  By the end of the outbreak at least 69 people became ill. 

Spinach E. coli Outbreak, August and September 2006

On Friday, September 8, 2006, Wisconsin Department of Health (WDOH) epidemiologists alerted officials at the Centers for Disease Control and Prevention (CDC) that a small cluster of E. coli O157:H7 infections with an unknown source had been identified.  Separately, the State of Oregon Public Health Division (ODPH) also noted a small cluster of E. coli infections that same day.  Both WDOH and ODPH uploaded the PFGE patterns, (genetic fingerprints), of the E. coli O157:H7 strains that had been isolated from victims from their respective states to PulseNet—an epidemiology tool that serves as an early warning system for outbreaks of foodborne illness that is comprised of a national network of public health laboratories that performs DNA “fingerprinting” on bacteria that may be foodborne.  PulseNet identifies and labels each “fingerprint” pattern and permits rapid comparison of these patterns through an electronic database at the CDC to identify related strains.  Through PulseNet, CDC became aware that the Wisconsin and Oregon outbreaks had been caused by an indistinguishable strain of E. coli, suggesting a common source.

On September 13, 2006, Wisconsin and Oregon health officials reported to CDC that interviews of ill individuals suggested the consumption of fresh-bagged spinach was common in both clusters, and on September 14, 2006, the Food and Drug Administration (FDA) warned the public not to eat fresh-bagged spinach.  By September 15, CDC had received nearly 100 reports of E. coli infection among residents of several states. 

The epidemiologic investigation into the outbreak indicated that the outbreak source was bagged spinach produced in a single plant, on a single day, during a single shift.  Between August 1 and October 6, 2006, public health officials identified 199 individuals infected with the outbreak strain of E. coli O157:H7 in 26 states; 102 were hospitalized, 31 developed HUS, and 5 died. 

Lettuce E. coli Outbreak, November 2006

On Jan 12, 2007, the Food and Drug Administration (FDA) announced that it had moved closer to identifying the source of an E. coli O157:H7 outbreak that had resulted in the approximately 81 illnesses in November and December of 2006.  Cases were reported in Minnesota (33), Iowa (47), and Wisconsin (1).  Twenty-six people were hospitalized, and two developed HUS.  The investigation into the outbreak revealed that all ill individuals had contracted E. coli after eating foods at chain Mexican food restaurants in Iowa and Minnesota.  Epidemiologic studies by Minnesota and Iowa health officials identified shredded iceberg lettuce served in the restaurants as the likely source of the outbreak.  Minnesota, Iowa, and Wisconsin health officials worked with public health agencies in California in a trace-back effort to determine where the E. coli-contaminated lettuce originated.  During the trace-back investigation the strain of E. coli O157:H7 associated with the outbreak was found in two environmental samples gathered from dairy farms near a lettuce field in California’s Central Valley.  The FDA was then able to locate the site where the lettuce was grown by reviewing records obtained from the lettuce processor.

Cookie Dough E. coli outbreak, 2009

On June 18, 2009, the Colorado Department of Public Health and Environment (CDPHE) issued a press release stating that CDPHE, the Centers for Disease Control and Prevention (CDC), and other state health departments were investigating an outbreak of E. coli O157:H7 infections in persons who had eaten raw pre-packaged, refrigerated cookie dough.  A joint investigation by state public health agencies, the CDC, and U.S. Food and Drug Administration resulted in the conclusion that at least 80 people in 30 states had become ill with E. coli O157:H7 infections after eating the contaminated cookie dough; 10 cases progressed to HUS. 

Waterborne Transmission of Stx-producing E. coli

Water intended for recreation (e.g., pools, shallow lakes) and for human consumption can also become contaminated.  When lakes become contaminated, several weeks or months can be required for water quality conditions to improve or return to normal. 

1998 E. coli outbreak at a water park

In 1998, an E. coli outbreak occurred among children who had visited a water theme park in the Southeast.  Health officials traced the outbreak to an infected toddler who played in a pool while wearing diapers.  Even though the pool was chlorinated, its concentration and contact time was presumably insufficient to kill the E. coli resulting from fecal contamination by the toddler, and other children who were in the pool ingested E. coli bacteria while playing in the pool. 

1998 E. coli outbreak associated with a municipal water system

Also in 1998, the municipal water system in Alpine, Wyoming, became contaminated with E. coli, resulting in 157 illnesses, with four people developing HUS.  The outbreak investigation revealed that the town’s water supply, which came from an unchlorinated underground spring, became contaminated with surface water prior to the outbreak. A large pool of water was found in the area over the water collection pipes, probably the result of a late snow melt combined with heavy rains and ground water outfalls.  In addition, investigators found numerous deer and elk feces were present in the pool area, as animals came to the pool to drink (Olsen, et al., 2002).

1999 E. coli outbreak associated with exposure to recreational water

E. coli contamination at a lake in Connecticut led to an E. coli outbreak in 1999.  Eleven people became ill with E. coli infections, and 3 children developed HUS; the attack rate was highest among those who were younger than 10 years who swam and/or swallowed water while swimming (McCarthy, et al., 2001; Tara, et al., 2001). 

1999 E. coli outbreak associated with well water

Also in 1999, the New York State Department of Health investigated what is believed to be the largest outbreak of waterborne E. coli O157:H7 illness in United States history. The outbreak occurred at a fair in Washington County, New York, in August of 1999 (New York State Department of Health and Novello, 2000, March).  A total of 781 persons were identified with suspected infections of E. coli O157:H7 and/or Campylobacter jejuni.  Of these cases 127 persons were culture-confirmed to be ill with E. coli O157:H7, 71 individuals were hospitalized, 14 persons exhibited HUS, and 2 people died. 

The environmental and site investigation indicated that unchlorinated water from a well serving the southwestern portion of the fairgrounds was contaminated with E. coli O157:H7 (DOH News, 1999, September 16).  Samples of manure collected from a barn located 50 feet from the well and samples from the groundwater flow from the manure storage area located 80 feet from the well tested negative for E. coli O157:H7.  However, samples from the septic system tested positive for E. coli O157:H7.

Consumption of only two food or beverage items, soda with ice or ice in any drink, was reported by a majority of the culture-confirmed case patients.  MMWR Weekly (1999) reported that the pulsed-field gel electrophoresis testing by the New York state laboratory indicated that the DNA fingerprints of E. coli O157:H7 isolates from the well, the water distribution system, and most confirmed cases were similar.

The epidemiological investigation of this outbreak concluded that a significant relationship was associated with the incidence of the outbreak and the consumption of beverages purchased from vendors supplied with water from the unchlorinated well.

Animal-to-Person Transmission of E. coli

Animal-to-person spread of E. coli also occurs, and has been identified in several outbreak-situations as well as in isolated settings, such as homes.

E. coli at Fairs and Petting Zoos

The mode of transmission for E. coli at agricultural fairs, petting zoos, and farm visits was previously thought to be limited to hand-to-mouth transmission following contact with contaminated surfaces or animals; however, recent indications are that inhalation of dust particles could potentially cause E. coli infection.  See www.fair-safety.com

Person-to-Person transmission of E. coli

Outbreaks of E. coli O157:H7 can also be caused by person-to-person transmission, which has occurred in daycare centers, hospitals, nursing homes, and private residences.  Because the infectious dose is so small it is very easy for the bacteria to be transmitted among people with close physical contact. 

2000 E. coli outbreak associated with a daycare

In August of 2000, a daycare in California was identified as the source of an E. coli O157:H7 outbreak.  Health department officials who investigated the outbreak determined that the probable “index case”—a child who unknowingly brought the bacteria into the facility—experienced “explosive diarrhea at the daycare on the afternoon of 8-3-00.”

Shortly thereafter, four other children became infected with E. coli O157:H7 on successive days, the 6th, 7th, 8th and 9th of August, 2000.  All of the children were in the same day care group.  In addition to the illnesses of the children, the mother of one child, and another child’s sibling became ill and tested positive for E. coli. Another toddler also became ill.

According to the Facility Evaluation Report by the Department of Social Services, “[t]he cause of the [E. coli O157:H7] outbreak was due to a sponge being used simultaneously for wiping down a changing table and wiping down a table used for serving meals.”

E. coli case associated with person-to-person contact

A toddler in Idaho who had mild non-bloody diarrhea routinely shared the family’s bathtub with a neighbor’s child.  Several days after the two children bathed together, the neighbor child developed bloody diarrhea that progressed to severe HUS.  A few days later, the first toddler was also admitted to the same children’s hospital with HUS.  Tragically, the neighbor’s child died.

E. coli case associated with person-to-person contact

A father who worked on a dairy farm contracted mild, non-bloody E. coli diarrhea that was transmitted to his son, who developed HUS.  The same event reoccurred two years later.  The son’s second episode was devastating.  Although the son survived, he was left with blindness and severe brain damage.

Symptoms of E. coli infection

What happens after the Shiga toxin-producing E. coli are ingested?

E. coli infection occurs when a person ingests Shiga toxin (Stx)-producing E. coli (e.g., E. coli O157:H7) after exposure to contaminated food, beverages, water, animals, or other persons.  After ingestion, E. coli bacteria rapidly multiply in the large intestine and bind tightly to cells in the intestinal lining.  This snug attachment facilitates absorption of the toxin into the small capillaries within the bowel wall, where it attaches to globotriaosylceramide (Gb3) receptors. 

Inflammation caused by the toxins is believed to be the cause of hemorrhagic colitis, the first symptom of E. coli infection, which is characterized by the sudden onset of abdominal pain and severe cramps, followed within 24 hours by diarrhea (Boyce, Swerdlow, & Griffin, 1995; Tarr, 1995).  Hemorrhagic colitis typically occurs within 2 to 5 days of ingestion of E. coli, but the incubation period, or time between the ingestion of E. coli bacteria and the onset of illness, may be as broad as 1 to 10 days. 

As the infection progresses, diarrhea becomes watery and then may become grossly bloody, that is, bloody to the naked eye.  E. coli symptoms also may include vomiting and fever, although fever is an uncommon symptom. 

On rare occasions, E. coli infection can cause bowel necrosis (tissue death) and perforation without progressing to hemolytic uremic syndrome (HUS)—a complication of E. coli infection that is now recognized as the most common cause of acute kidney failure in infants and young children.  In about 10 percent of E. coli cases, the Shiga toxin attachment to Gb3 receptors results in HUS. 

HUS had been recognized in the medical community since at least the mid-1950’s; however, the syndrome first caught the public’s attention in 1993 following a large E. coli outbreak in Washington State that was linked to the consumption of contaminated hamburgers served at a fast-food chain.  A total of 501 E. coli cases were reported; 151 were hospitalized (31 percent), 45 persons (mostly children) developed HUS (9 percent), and three died (Bell, et al., 1994).

During HUS, the majority of the toxin gains access to the systemic circulation where it becomes attached to weak receptors on white blood cells (WBC) thus allowing the toxin to “ride piggyback” to the kidneys where it is transferred to numerous strong Gb3 receptors that grasp and hold on to the toxin. 

Organ injury is primarily a function of Gb3 receptor location and density.  These receptors are probably always in the gut wall and kidneys, but heterogeneously distributed in the other major body organs.  This may be the reason that some patients develop injury in other vital organs (e.g., brain, etc).  Once Stx attaches to receptors, it moves into the cells’ cytoplasm where it shuts down the cells’ protein machinery resulting in cellular injury or death, and subsequent damage to vital organs such as the kidney, pancreas, and brain. 

Treatment for E. coli infection

Treatment for an E. coli Infection

In most infected individuals, symptoms of E. coli infection last about a week and resolve without any long-term problems.  Antibiotics do not improve the illness, and some medical researchers believe that these medications can increase the risk of developing post-diarrheal hemolytic uremic syndrome (D+HUS) (Wong, Jelacic, & Tarr, 2000).  Therefore, apart from good supportive care such as close attention to hydration and nutrition, there is no specific therapy to halt E. coli symptoms.  The recent finding that E. coli O157:H7 initially greatly speeds up blood coagulation may lead to future medical therapies that could forestall the most serious consequences (Chandler, et al., 2002).  Most individuals who do not develop D+HUS recover within two weeks. 

Treatment for those who develop HUS ranges from mild to very intensive.  Children are generally in the hospital for about two weeks (range 3 days to 3 months), and adults longer, as their courses tends to be more severe.  Since there is no way to end D+HUS, supportive therapy, including meticulous attention to fluid and electrolyte balance, is the cornerstone of survival.  For more information about the treatment for HUS, read “What to expect during hospitalization” at About-Hus.com.  

Preventing E. coli Infection

What can we do to protect our families from E. coli?

Since there is no fail-safe food safety program, consumers need to “drive defensively” as they navigate from the market to the table.  It is no longer sufficient to take precautions only with ground beef and hamburgers, anything ingested by family members can be a vehicle for infection.  Shiga toxin-producing E. coli are now so widely disseminated that a wide variety of foods can be contaminated.  Direct animal-to-person and person-to-person transmission is not uncommon.  Following are steps you can take to protect your family from E. coli.  See also the section What is our government doing to protect us from E. coli?, below.

1. Practice meticulous personal hygiene.  This is true not only for family members (and guests), but for anyone interfacing with the food supply chain.  Remember that E. coli bacteria are very hardy (e.g., can survive on surfaces for weeks) and that only a few are sufficient to induce serious illness.  Since there is no practical way of policing the hygiene of food service workers, it is important to check with local departments of health in order to identify any restaurants that have been given citations or warnings.  The emerging practice of providing sanitation “report cards” for public display is a step in the right direction.
2. Be careful to avoid cross contamination when preparing and cooking food, especially if beef is being served.  This requires being very mindful of the surfaces (especially cutting boards) and the utensils used during meal preparation that have come in contact with uncooked beef and other meats.  This even means that utensils used to transport raw meat to the cooking surfaces should not be the same that are later used to remove the cooked meat (or other foodstuffs) from the cooking surfaces.
3. Do not allow children to share bath water with anyone who has any signs of diarrhea or “stomach flu”.  And keep any toddlers still in diapers out of all bodies of water (especially wading and swimming pools).
4. Do not let any family members touch or pet farm animals.  Merely cleaning the hands with germ “killing” wipes may not be adequate!
5. Wear disposable gloves when changing the diapers of any child with any type of diarrhea.  Remember that E. coli O157:H7 diarrhea initially is non-bloody, but still very infectious.  If gloves are not available, then thorough hand washing is a must.
6. Remember that achieving a brown color when cooking hamburgers does not guarantee that E. coli bacteria have been killed.  This is especially true for patties that have been frozen.  Verifying a core temperature of at least 160 degrees Fahrenheit for at least 15 seconds is trustworthy.  Small, disposable meat thermometers are available, a small investment compared to the medical expense (and grief) of one infected family member.
7. Avoid drinking (and even playing in) any non-chlorinated water.  There is an added risk if the water (well, irrigation water or creek/river) is close to, or downstream from any livestock.

Irradiation offers the most practical and effective way of sterilizing foods and protecting the consumer.  It is already being used for poultry, and is approved for all other foods.  Even though the word “irradiation” conjures up fears of radiation exposure, irradiated food does not become “radioactive”; it is safe, and does not change the taste or texture of food.  To insure safety the public needs to be educated and the food industry convinced that this will not only protect the consumer, but also will also favorably affect their bottom line.  This should be a “no-brainer” given the fact that contaminated foods are costing the food industry hundreds of millions of dollars a year (recently, one beef processing company declared bankruptcy following a massive recall of contaminated hamburgers).  If this doesn’t work, the food industry may be required to implement this or other equally effective measures. 

What is our government doing to protect us from E. coli?

Congress enacts statutes designed to ensure the safety of the food supply.  The U.S. food agencies are accountable to the President; to the Congress, which has oversight authority; to the courts, which review regulations and enforcement actions; and to the public. The principal federal agencies responsible for providing consumer protection are:

1. U.S. Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS) has the responsibility for ensuring that meat, poultry, and egg products are safe, wholesome, and accurately labeled.
2. Food and Drug Administration (FDA) is charged with protecting consumers against impure, unsafe, and fraudulently labeled food other than in areas regulated by the Food Safety and Inspection Service (FSIS).
3. Centers for Disease Control and Prevention (CDC), is part of the Department of Health and Human Services (DHHS), and has a food safety mission that falls within its surveillance and outbreak response activities, but that is unlike those of USDA and FDA. CDC does not have regulatory authority.  Even so, it is the lynch pin of our county’s food safety program.  Its pivotal role is exemplified by the following excerpts:

On Nov. 15, 2006, a senior official from CDC testified before the Senate Committee on Health, Education, Labor and Pensions, regarding CDC’s food safety activities, with a special emphasis on the recent E. coli spinach outbreak (King, 2006, November 15).  He testified, in part, that: 

As an agency within the Department of Health and Human Services (HHS), CDC leads federal efforts to gather data on foodborne illnesses, investigate foodborne illnesses and outbreaks, and monitor the effectiveness of prevention and control efforts. CDC is not a food safety regulatory agency but works closely with the food safety regulatory agencies, in particular with HHS’s Food and Drug Administration (FDA) and the Food Safety and Inspection Service (FSIS) within the United States Department of Agriculture (USDA). CDC also plays a key role in identifying prevention strategies and building state and local health department epidemiology, laboratory, and environmental health capacity to support foodborne disease surveillance and outbreak response. Notably, CDC data are used to help document the effectiveness of regulatory interventions.
In partnership with state health departments, CDC collects surveillance information on foodborne illness. The states collect data about cases of infections that are of public health importance from doctors and clinical laboratories. CDC helps states investigate outbreaks that are large, severe, or unusual. . . .
CDC specializes in the critically important public health activities of surveillance, epidemiologic response, and investigation of disease. . . .
In 1993, there was a large multi-state outbreak of E. coli O157 infections in the Western United States. In order to prevent future severe outbreaks . . . an effective surveillance network called PulseNet was developed.  PulseNet is the national network for molecular sub-typing of foodborne bacteria . . . and is coordinated by CDC. The laboratories participating in PulseNet are in state health departments, some local health departments, USDA, and FDA. PulseNet plays a vital role in surveillance for, and investigation of, foodborne illness outbreaks that were previously difficult to detect. For example, when a clinical laboratory makes a diagnosis of E. coli O157, the bacterial strain is sent to a participating PulseNet laboratory where it is sub-typed, or “DNA fingerprinted” [every E. coli has a unique DNA pattern].  The “fingerprint” is then compared with other patterns in the state, and uploaded electronically to the national PulseNet database maintained at CDC, where it can be compared with the patterns in other states. This gives us the capability to rapidly detect a cluster of infections with the same pattern that is occurring in multiple states. The PulseNet database, which includes approximately 120,000 DNA patterns, is available to participating laboratories and allows them to rapidly compare patterns. Once a cluster of cases with the same DNA pattern is identified, epidemiologists then interview patients to determine whether cases of illness are linked to the same food source or other exposures they have in common. The strength of this system is its ability to identify patterns even if the affected persons are geographically far apart, which is important given the reality of U.S. food distribution systems. If patients have been exposed to a specific food or to another source of infection, and the case count for that illness is larger than one would expect for the time period, the cluster is determined to be an outbreak with a common source.
The group of epidemiologists in the states and at CDC who regularly investigate and report on these outbreaks is called OutbreakNet. The Outbreak Net participants use standardized interview methods and forms and rapidly share the investigation data. With this collaboration, outbreaks can be investigated in a matter of days rather than weeks. As a consequence, CDC [that has no regulatory authority] can more rapidly alert FDA and USDA about implicated food products associated with foodborne illness so that all three agencies can collaboratively take actions to protect public health. Tracing the implicated food back from consumption through preparation, to distributors, and sometimes back to a field or farm can help determine how the contamination occurred, stop distribution of the contaminated product, and prevent further outbreaks from occurring. . . .
Another important surveillance network is CDC’s Foodborne Diseases Active Surveillance Network (FoodNet). This network is collaboration among 10 state health departments, the USDA, and FDA . . . FoodNet conducts active surveillance for foodborne diseases and also conducts related epidemiologic studies that look at both sporadic and outbreak foodborne infections to help public health officials better understand the epidemiology of foodborne diseases in the United States and how to target prevention strategies. We have PulseNet to detect possible outbreaks, OutbreakNet to investigate and report them, and FoodNet to track general trends and define where more effective prevention strategies are needed (emphasis added).
These networks stand prepared to detect a public health event related to the food supply. For example, after investigations of PulseNet-identified clusters of E. coli infection focused attention on the need for specific controls during ground beef processing, regulatory and industry practices changed in 2002, and the incidence of E. coli O157:H7 infections began to decrease sharply.  By 2005, the incidence of E. coli O157 infections, as measured in FoodNet, had dropped 29% [Since 2006, however, the incidence appears to be rising, primarily due to outbreaks linked to lettuce and spinach].

good luck

Mohamed Hassaan

Cryptosporidium parvum

 Cryptosporidium parvum

Introduction

Cryptosporidium is a coccidian protozoan parasite that has gained much attention in the last 20 years as a clinically important human pathogen. The discovery of Cryptosporidium is usually associated with E.E. Tyzzer, who, in 1907, described a cell-associated organism in the gastric mucosa of mice (Keusch, et al., 1995). For several decades, Cryptosporidium was thought to be a rare, opportunistic animal pathogen, but the first case of human cryptosporidiosis in 1976 involved a 3-year-old girl from rural Tennessee who suffered severe gastroenteritis for two weeks (Flanigan and Soave, 1993). Electron microscopic examination of the intestinal mucosa led to the discovery that Cryptosporidium parvum was the infectious species in humans. In the early 1980s, the strong association between cases of cryptosporidiosis and immunodeficient individuals (such as those with AIDS--acquired immunodeficiency syndrome) brought Cryptosporidium to the forefront as a ubiquitous human pathogen. Presently, the increasing population of immunocompromised persons and the various outbreaks of cryptosporidiosis through infection by water-borne Cryptosporidium oocysts (often in drinking water) have placed an even greater emphasis on this pathogen. Little is known about the pathogenesis of the parasite, and no safe and effective treatment has been successfully developed to combat cryptosporidiosis (Juranek, 1995). Unlike other intestinal pathogens, Cryptosporidium can infect several different hosts, can survive most environments for long periods of time due to its "hardy cyst" (Keusch, et al., 1995), and inhabits all climates and locales. Below is a duodenal biopsy sample from a patient with AIDS and cryptosporidiosis (Flanigan and Soave, 1993; arrows point to the parasites in the microvillus border):

Life Cycle

Cryptosporidium is taxonomically classified as a Sporozoa, since its oocyst releases four sporozoites (its motile infectious agents) upon excystation. However, it differs from related parasites such as Toxoplasma by its monoxenous life cycle--completing its entire cycle within a single host (Flanigan and Soave, 1993). The life cycle is complex; there are both sexual and asexual cycles, and there are six distinct developmental stages (Keusch, et al., 1995):

1. Excystation of the orally ingested oocyst in the small bowel with release of the four sporozoites
2. Invastion of intestinal epithelial cells via the differentiated apical end of the sporozoite within a vacuole formed of both host and parasite membranes and the initiation of the asexual intracellular multiplication stage
3. Differentiation of microgametes and macrogametes
4. Fertilization initiating sexual replication
5. Development of oocysts
6. The formation of new, infectious sporozoites within the oocyst, which is then excreted in the stool

The cycle begins anew when these oocysts are ingested by a new host. Below is a visual representation of the Cryptosporidium life cycle (Heyworth, 1992):

Clinical manifestations

The various symptoms of cryptosporidiosis differ greatly between immunocompetent and immunocompromised individuals. In immunocompetent patients, cryptosporidiosis is an acute, yet self-limiting diarrheal illness (1-2 week duration), and symptoms include (Juranek, 1995):

• Frequent, watery diarrhea
• Nausea
• Vomiting
• Abdominal cramps
• Low-grade fever

For immunocompromised persons, the illness is much more severe (Juranek, 1995):

• Debilitating, cholera-like diarrhea (up to 20 liters/day)
• Severe abdominal cramps
• Malaise
• Low-grade fever
• Weight loss
• Anorexia

Due to lack of tissue specificity, C. parvum infection has also been identified in the biliary tract (causing thickening of the gallbladder wall) and the respiratory system (Casemore, et al., 1994).

Epidemiology

Infection by C. parvum has been reported in six continents and identified in patients aged 3 days to 95 years old (Flanigan and Soave, 1993). Transmission is usually fecal-oral, often through water contaminated by livestock mammal feces. Persons most likely to be infected by Cryptosporidium are:

• infants and younger children in day-care centers
• those whose drinking water is unfiltered and untreated
• involved in farming practices such as lambing, calving, and muck-spreading
• engaging in sexual practices that brings a person into oral contact with feces of an infected individual
• patients in a nosocomial setting with other infected patients or health-care employees
• veterinarians who come in contact with farm animals
• travelers to areas with untreated water
• living in densely populated urban areas
• owners of infected household pets (rare)

(Keusch, et al., 1995; Casemore, et al., 1994; Goodgame, 1996; Juranek, 1995; Flanigan and Soave, 1993)

Within a population of immunocompromised individuals, severe and persistent disease has been associated with persons with CD4 counts of <180 cell/cubic mm (Juranek, 1995).

Transmission

Cryptosporidial infection can thus be transmitted from fecally contaminated food and water, from animal-person contact, and via person-person contact. The probability of transmission from just a small amount of contamination is fairly high, since a recent study has determined that the 50% infective dose (ID50) of C. parvum is only 132 oocysts for healthy persons with no previous serological immunity to cryptosporidiosis (DuPont, et al., 1995).

Food and water

There have been six major outbreaks of cryptosporidiosis in the United States as a result of contamination of drinking water (Juranek, 1995). One major outbreak in Milwaukee in 1993 affected over 400,000 persons. Outbreaks such as these usually result from drinking water taken from surface water sources such as lakes and rivers (Juranek, 1995). Swimming pools and water park wave pools have also been associated with outbreaks of cryptosporidiosis. Also, untreated groundwater or wellwater public drinking water supplies can be sources of contamination.

The highly environmentally resistant cyst of C. parvum allows the pathogen to survive various drinking water filtrations and chemical treatments such as chlorination. Although municipal drinking water utilities may meet federal standards for safety and quality of drinking water, complete protection from cryptosporidial infection is not guaranteed. In fact, all waterborne outbreaks of cryptosporidiosis have occurred in commmunities where the local utilities met all state and federal drinking water standards (Juranek, 1995). For more information about drinking water and cryptosporidiosis, click here.

Food can also be a source of transmission, when either an infected person or an asymptomatic carrier contaminates a food supply. The first documentation of this type of infection occurred at a county fair in Maine, where children who drank apple cider contaminated by animal feces developed cryptosporidiosis (Juranek, 1995). The oocysts do not survive cooking, but food contamination can occur in beverages, salads, or other foods not heated or cooked after handling.

Animal-person transmission

Transmission of C. parvum from household pets is extremely rare, but there is a definite correlation between calves and humans--approximately 50% of calves shed oocysts and the pathogen is present on upwards of 90% of all dairy farms (Juranek, 1995).

Person-person transmission

Cryptosporidium transmission occurs at a high frequency in day-care centers, where infants or younger children are clustered within classrooms, share toilets and common play areas, or necessitate frequent diaper-changing (Keusch, et al., 1995). Day-care employees can become easily infected by C. parvum through careless diaper-changing or through washing the laundry of infected children. Day-care workers can then spread the pathogen to their families at home.

Nosocomial settings are also a major forum for cryptosporidial transmission. There have been several reports of both transmission from patients to health care staff and patient-to-patient transmission. An outbreak in a bone-marrow transplant unit occurred where five patients developed cryptosporidiosis after a sixth, infected patient was admitted to the unit (Casemore, et al., 1994). Another major outbreak occurred in North Wales after a terminally ill AIDS patient infected with cryptosporidiosis was admitted to the infectious diseases unit of a major hospital. Five cases of cryptosporidiosis were confirmed among the nursing staff, and infection most likely occurred from major environmental contamination due to the patient's intractable diarrhea and vomiting (Casemore, et al., 1994). This "environmental contamination" raises the possibility of aerosol transmission of C. parvum from person-to-person. Various routes of transmission such as aerosol infection is fairly likely, since Cryptosporidium oocysts are shed in large numbers during acute infection and are immediately infective to others (Casemore, et al., 1994). These nosocomial outbreaks signal the need for hospitals to take extreme enteric precautions upon admittance of infected patients. And, health-care staff should report even minor gastrointestinal symptoms to prevent transmission to other staff and patients.

Pathogenesis

Upon oocyst excystation, four sporozoites are released which adhere their apical ends to the surface of the intestinal mucosa (Keusch, et al., 1995). Below is a phase contrast photograph of sporozoite release from the Cryptosporidium oocyst (Flanigan and Soave, 1993):

A sporozoite-specific lectin adherence factor has been identified as the agent of attachment to the intestinal surface (Keusch, et al., 1995). After sporozoite attachment, it has been hypothesized that the epithelial mucosa cells release cytokines that activate resident phagocytes (Goodgame, 1996). These activated cells release soluble factors that increase intestinal secretion of water and chloride and also inhibit absorption. These soluble factors include histamine, serotonin, adenosine, prostaglandins, leukotrienes, and platelet-activating factor, and they act on various substrates, including enteric nerves and on the epithelial cells themselves (Goodgame, 1996). Consequently, epithelial cells are damaged by one of two models:

1. Cell death is a direct result of parasite invasion, multiplication, and extrusion or
2. Cell damage could occur through T cell-mediated inflammation, producing villus atrophy and crypt hyperplasia

Either model produces distortion of villus architecture and is accompanied by nutrient malabsorption and diarrhea (Goodgame, 1996). Experimental evidence supporting this pathogenic hypothesis exists in a pig model system, where decreased intestinal sodium absorption has been correlated with "both decreased villus surface area and inhibition by prostaglandin E2 produced by inflammatory cells" (Goodgame, 1996).

Detection and Diagnosis

When C. parvum was first identified as a human pathogen, diagnosis was made by a biopsy of intestinal tissue (Keusch, et al., 1995). However, this method of testing can give false negatives due the "patchy" nature of the intestinal parasitic infection (Flanigan and Soave, 1993). Staining methods were then developed to detect and identify the oocysts directly from stool samples. The modified acid-fast stain is traditionally used to most reliably and specifically detect the presence of cryptosporidial oocysts (image from Ortega, et al., 1993):

Immunologically, anti-cryptosporidial IgM, IgG, and IgA can be detected by the enzyme-linked immunoabsorbent assay (ELISA) or by the antibody immunofluorescence assay (IFA), but neither of these assays can provide a direct diagnosis of cryptosporidiosis.

Recently, new genetic methods of detecting C. parvum have been developed, using PCR (Polymerase Chain Reaction) or other DNA-based detection methods. For more information about these improvements in the specificity and sensitivity of cryptosporidial detection, click here.

Treatment

No safe and effective therapy for cryptosporidial enteritis has been successfully developed. Since cryptosporidiosis is a self-limiting illness in immunocompetent individuals, general, supportive care is the only treatment for the illness. Oral or intravenous rehydration and replacement of electrolytes may be necessary for particularly voluminous, watery diarrhea. Oral rehydration treatment can include Gatorade, bouillon, or oral rehydration solution, containing glucose, sodium bicarbonate, and potassium (Flanigan and Soave, 1993).

Pharmocological therapies

For immunocompromised patients with cryptosporidiosis, several antimicrobial agents have been tested as possible treatments for the illness. Antibiotics such as spiramycin and dicalzuril sodium have produced partial responses in patients (a partial decrease in diarrhea or partial decrease in stool oocyst number), but have not yielded reliable, reproducible results (Flanigan and Soave, 1993). However, one particular antimicrobial agent, paromomycin, has been shown to decrease the intensity of infection and improve intestinal function and morphology (Goodgame, 1996). Paromomycin is a poorly absorbed, broad spectrum antibiotic similar to neomycin, and in a review of 12 patients with 23 episodes of gastrointestinal cryptosporidiosis, 16 of the 23 epidoses had a complete response to therapy (symptom improvement, diarrhea eradication, and weight gain) and the other seven episodes had a partial response (Flanigan and Soave, 1993). However, relapse after treatment is common and fairly expensive maintenance therapy is often necessary.

Immunologic therapy

Although serological antibodies do not provide protection from cryptosporidial infection, several studies have been done to show that antibodies in the intestinal lumen may help clear or even prevent infection. The feeding of bovine colostral immunoglobulin to patients has been shown to ameliorate symptoms of Cryptosporidium infection in humans (Heyworth, 1992), and it has also been shown that the release of intestinal IgA accompanies this clearance of infection. In addition, anti-sporozoite antibodies have blocked the infectivity of C. parvum sporozoites in mice by inhibiting their ability to attach to the surface of the intestininal mucosa. A more recent study by Doyle, et al. (1993), reproduced the inhibition of C. parvum infection by hyperimmune bovine colostrum in vitro, providing an ideal system through which cryptosporidial infection can be studied in the laboratory. The mean number of intracellular parasites per host cell was reduced by 61% upon introducing HBC Ig antibodies with a concentration of 1 mg/ml IgG. This investigation also purified antibodies from HBC Ig on Western blots of Cryptosporidium proteins and found that they, too, inhibited C. parvum infectivity in vitro. Lastly, this team of investigators identified 19 sporozoite surface antigens which are recognized by HBC Ig. This system of immunotherapy (intraluminal gastric administration of HBC to immunocompromised patients) is a big step forward in finding an efficacious treatment for cryptosporidiosis. However, a combination of pharmacologic and immunologic therapy may be the most effective scenario for combating C. parvum infection in immunodeficient persons.

Drinking water: purification and filtration

Home use

Current data is not adequate to advise all immunodeficient persons to boil or avoid tap water, but the risks involved are high enough that, until the health risk of drinking water containing small number of Cryptosporidium oocysts is clearly defined, it is advised that these individuals boil all water intended for drinking for at least one minute.

If one does not want to boil water constantly, a household water filtration system or drinking bottled water can reduce the risk of Cryptosporidium infection. When selecting a filtration system, the system should have one or all of the following characteristics (Juranek, 1995):

• it can remove particles that are 0.1-1 micrometers in size
• filters water by reverse osmosis
• it has an "absolute" 1-micron filter
• meets NSF standard no. 53 for "cyst removal"

On the other hand, filters that have the following characteristics do NOT guarantee >99% removal of Cryptosporidium oocysts (Juranek, 1995):

• filters with a "nominal" 1-micron rating
• only employs ultraviolet light
• uses only activated carbon for filtration
• utilizes pentiodide-impregnated resins
• it is effective against Giardia species

When selecting a high-quality bottled water, one should question the vendor directly to see if the filtration systems used to purify the bottled water matches the characteristics in the first list above (removal of >99% oocysts). In either case, careful research is needed to ensure protection from Cryptosporidium infection from drinking water at home, especially for immunocompromised individuals.

Municipal systems

Municipal water utilities provide relatively good protection against water-borne Cryptosporidium infection. There were only six major documented cases of cryptosporidiosis outbreaks via drinking water between 1984-1994, even though the 1993 outbreak in Milwaukee caused over 400,000 cases (Jakubowski, 1995). Since this massive outbreak, much more research has been done to eliminate the possibility of further outbreaks via public drinking water.

Municipal drinking water is purified two ways: through chemical treatments and through filtration. Chemically, chlorination is used most frequently to safely disinfect drinking water by killing most viruses, bacteria, and protozoa like Giardia, but studies have shown that Cryptosporidium is 240,000 times more resistant to chlorination than Giardia (Jakubowski, 1995), and C. parvum oocyst viability was not affected by exposure to 1.05 and 3% chlorine for up to 18 hours (Korich, et al., 1990). Also, Korich, et al., found that chlorine dioxide and monochloramine were also ineffective in inactivating C. parvum oocysts in drinking water. Excystation and mouse infectivity were evaluated to assess oocyst viability. This study did find that treating oocysts with 1 ppm (1 mg/liter) of ozone for five minutes inactivated over 90% of the oocysts, but drinking water standards dictate that a maximum of only 0.4 mg of ozone per liter of water is allowed (Juranek, 1995). Thus, although ozone may be a potential disinfectant for inactivating C. parvum oocysts, one should not assume that these traditional chemical disinfectants (even if they inactivate coliform bacteria and Giardia) effectively eliminate the risk of cryptosporidial infection.

Filtration is a better bet for removing C. parvum oocysts from municipal drinking water. In recent years, ultra-fine membranes have been developed to remove various contaminants from drinking water. Below is a typical membrane process unit from Mount Vernon, Ohio (five miles from Kenyon College!):

The following is the removal size ranges of membrane processes (1 micron = .0000394 inches):

• 5-100 microns: conventional filtration, removes human hair, the smallest particles visible to the naked eye and red blood cells
• 0.1-5 microns: micro filtration, removes the smallest yeast cells, tobacco smoke, and the smallest bacteria
• 0.01-0.1 microns: ultra filtration, removes carbon black and is in the range of an electron microscope
• 0.001-0.01 microns: reverse osmosis, removes particles in the ionic range, such as the polio virus, aqueous salts, and metal ions (Camp Dresser and McKee, 1995)

Thus, since C. parvum oocysts can be as small as 4 microns (Flanigan and Soave, 1993), at least micro filtration is needed to reliably remove oocysts from the water supply. Since Cryptosporidium oocysts are so resistant to chemical disinfectants, ultra filtration or reverse osmosis would provide ideal protection against waterborne outbreaks via drinking water.

Recent Progress and Future Directions

PCR detection of C. parvum oocysts

Genetic methods for detecting oocysts have been developed that identify and amplify Cryptosporidium nucleic acids using the Polymerase Chain Reaction (Johnson, et al., 1995). Oocysts were detected by PCR in wastewater, surface waters, and drinking water, but the sensitivity of the PCR assay was inhibited by "uncharacterized components in the samples." The study went on to find that flow cytometry, dot blot, and magnetic antibody capture improved the sensitivity of the PCR assay.

A month later, in December of 1995, a test was developed that not only specifically and sensitively detected C. parvum oocysts by PCR (it amplified an 873-bp region of a 2359-bp DNA fragment encoding a repetitive oocyst protein), it reported the oocysts' viability (Wagner-Wiening and Kimmig, 1995). Direct use of PCR did not distinguish between live and dead oocysts, since oocyst DNA is apparently preserved at least a week after cell death. However, PCR was then used to detect target DNA of excysted sporozoites after incubation in excystation medium. Thus, viability of oocysts was determined by detecting and amplifying a viable sporozoite DNA fragment. These protocols are adequate to detect low numbers of viable oocysts, such as during "routine monitoring of drinking water and environmental samples" (Wagner-Wiening and Kimmig, 1995).

Future directions

Since Cryptosporidium has the potential to infect many people from a point-source outbreak, much research still needs to be done to (adapted from Juranek, 1995 and Keusch, et al., 1995):

• clarify the relationship between low numbers of oocysts in drinking water and the frequency of cryptosporidial infection
• determine the asymptomatic carrier rate for Cryptosporidium in immunocompromised persons and the chance that these individuals will develop cryptosporidiosis when their CD4 counts drop to a low level
• calculate the relative risks of infection from drinking water, contact with animals, unsafe sexual practices, and nosocomial contact to see where focus on preventative strategies should be placed
• improve state and federal communication for reporting cases of cryptosporidiosis and identifying outbreaks
• continue to develop more effective therapies for ameliorating cryptosporidiosis symptoms

REFERENCES

Camp, Dresser, and McKee. "Summary of the Mt. Vernon, Ohio, Membrane Softening Pilot Plant." December 14, 1995.

Casemore, D.P., Garder, C.A., and O'Mahony, C. "Cryptosporidial infection, with special reference to nosocomial transmission of Cryptosporidium parvum: a review." Folia Parasitol, 1994; 41 (1): 17-21.

Doyle, P.S., Crabb, J., and Petersen, C. "Anti-Cryptosporidium parvum antibodies inhibit infectivity in vitro and in vivo." Infect Immun, 1993 Oct; 61 (10): 4079-84.

Flanigan, T.P. and Soave, R. "Cryptosporidiosis." Prog Clin Parasitol, 1993; 1-20.

Goodgame, R.W. "Understanding intestinal spore-forming protozoa: cryptosporidia, microsporidia, isospora, and cyclospora." Ann Intern Med, 1996 Feb 15; 124 (4): 429-41.

Heyworth, M.F. "Immunology of Giardia and Cryptosporidium infections." J Infect Dis, 1992 Sep; 166 (3): 465-72.

Jakubowski, W. "Giardia and Cryptosporidium: The Details." 1995 Safe Drinking Water Act Seminar, U.S. Environmental Protection Agency.

Johnson, D.W., Pieniazek, N.J., Griffin, D.W., Misener, L., and Rose, J.B. "Development of a PCR protocol for sensitive detection of Cryptosporidium oocysts in water samples." Appl Environ Microbiol, 1995 Nov; 61 (11): 3849-55.

Juranek, D.D. "Cryptosporidiosis: sources of infection and guidelines for prevention." Clin Infect Dis, 1995 Aug; 21 Suppl 1: S57-61.

Keusch, G.T., Hamer, D., Joe, A., Kelley, M., Griffiths, J., and Ward, H. "Cryptosporidia--who is at risk?" Schweiz Med Wochenschr, 1995 May 6; 125 (18): 899-908.

Korich, D.G., Mead, J.R., Madore, M.S., Sinclair, N.A., and Sterling, C.R. "Effects of ozone, chlorine dioxide, chlorine, and monochlorine on Cryptosporidium parvum oocyst viability." Appl Envion Microbiol, 1990 May; 56 (5): 1423-8.

Wagner-Wiening, C., and Kimmig, P. "Detection of viable Cryptosporidium parvum oocysts by PCR." Appl Environ Microbiol, 1995 Dec; 61 (12): 4514-6.

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