Cryptosporidium Outbreak in a Continuously Tested Public Water Supply

Introduction The Department of Public Health and Planning in the Midland Health Board (MHB) was notified of nine confirmed and two suspected cases of cryptosporidiosis on the 3 June 2004. All of the cases were on the same water supply that services approximately 25,000 people. This supply had been the source of an outbreak of cryptosporidiosis in April/May 2002. As a result of the 2002 outbreak a filtration system was installed in December 2003. However, due to a high demand on the water supply and an inability of the system to deal with the high turbidity of the water the local authority added unfiltered water to the filtered water at a ratio of 1:4. The local authority carried out testing for Cryptosporidium on a daily basis when they started using the unfiltered water. The water supply had also been tested for Clostridium perfringens, an indicator organism for Cryptosporidium.