Cryptosporidium in water supplies

Revised December 2011

Cryptosporidium is a parasite which can produce an unpleasant gastric illness known as cryptosporidiosis. The parasite is transmitted in an encysted form known as an oocyst. At the present time there is nothing to treat cryptosporidiosis other than the body's defence systems. Cryptosporidiosis can, therefore, be a serious problem in people with weak immune systems such as young children, the elderly, people on cytotoxic drugs and those suffering from AIDS. Cryptosporidium is the third leading cause of non-viral gastro-intestinal illness in the UK.

There are a number of different species and strains of the parasite, but those which can infect human beings are also capable of infecting some animals, and vice versa.

Cryptosporidium is frequently waterborne in natural waters and infections have occurred from drinking contaminated water supplies. However, there are many other possible sources of infection such as zoonosis (animal-person contact), contaminated food and contaminated swimming pools and other recreational waters (rivers and lakes), or foreign travel.

A well-operated drinking water treatment plant can physically remove over 99.99% of oocysts from an affected raw water. Traditional processes such as coagulation, clarification and filtration remain the best defence against this parasite entering supplies. However, high risk sites are required to remove or render harmless any oocysts present based on raw water analysis and site specific risk assessments.

Chemical disinfectants are not generally effective against Cryptosporidium however a barrier method (membranes) and/or UV treatment are the only truly effective treatments at high risk sites.

Since 2007 in the UK the regulations are no longer specific for the control of Cryptosporidium, however water companies are now required to design and continuously operate adequate treatment and disinfection. Any oocysts found in the final treated water need to be reported to the DWI so the inspectorate can make checks to confirm if the regulations were contravened or any offences committed.

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