Thames Water's Experiences with Cryptosporidium

Abstract

In February 1989 an outbreak of waterborne cryptosporidiosis associated with contaminated surface water in the upper Thames catchment was identified. Less than 0.01% of the population suffered symptoms sufficient for them to seek medical advice. Nevertheless, the impact of the outbreak on the community and the water undertakers was considerable, and an expert committee was appointed by the Secretary of State for Health to advise on research and measures to control the disease and prevent future waterborne outbreaks. One of the committee's interim recommendations was for the gathering of information on the occurrence of cryptosporidium oocysts in the aquatic environment particularly sources used for abstraction and production of drinking water. The results of monitoring in the River Thames catchment will be discussed particularly in light of observations that peak contamination events occur in rivers which pass through agricultural land but do not receive discharges from sewage treatment works.