Advice on the response from public and environmental health to the detection of cryptosporidial oocysts in treated drinking water. PHLS Advisory Committee on Water and the Environment

New water quality regulations in the United Kingdom (UK) will lead to the regular sampling of water supplies for the presence of cryptosporidial oocysts. It is likely therefore that consultants in communicable disease control (CCDCs) and environmental health officers (EHOs) will be informed of the presence of oocysts in water supplies rather more often. These guidelines were developed, by an ad hoc working group of the PHLS Advisory Committee on Water and the Environment, to help CCDCs and EHOs respond to such reports. The implications for public health of oocysts in treated water supplies is still not fully understood. Nevertheless, on the basis of the available evidence, these guidelines suggest an approach to planning, to deciding what information is required on initial contact, and an approach to health risk assessment. The guidelines also suggest possible strategies for managing such situations. It is accepted, however, that the vast majority of reports of positive samples will require no intervention. It is essential that CCDCs and EHOs work well with their colleagues in the water companies in undertaking a health risk assessment and responding appropriately.