CRYPTOSPORIDIUM IN WATER Final report to the Department of the Environment January 1990 to March 1994
Report No DWI0268

Jan 1995

SUMMARY

After the outbreak of waterborne cryptosporidiosis in Swindon and Oxfordshire in 1989 a Group of Experts, under the Chairmanship of Sir John Badenoch, was established jointly by the Secretary of State for the Environment and the Secretary of State for Health. The Group's report made a number of recommendations and identified areas where more research was required. As a result of the recommendations a national programme of research was established involving work funded by the industry and government.

This report presents the results of studies carried out between January 1990 and March 1994 on those parts of the National Programme funded by the Department of the Environment. The responsibilities under the contract also required WRc to provide the secretariat to the National Cryptosporidium Research Programme Steering Committee.

In the areas of isolation, identification and enumeration of oocysts the work has confirmed that the established methods are generally imprecise and unreliable, although cross-flow filtration with separation aided by magnetisable particles, shows promise. A literature review identified a number of recently developed technologies that have potential for improved recovery and identification techniques. One major achievement of the studies was the development of a test for viability of oocysts using a dye inclusion/exclusion technique.

The dose required to initiate infection in humans is still unclear with contradictory results arising from the two studies in this programme. The results do, however, support evidence of differences of strain or virulence within the species of Cryptosporidium parvum.

Studies of occurrence indicate that oocysts are frequently present in low numbers in surface waters and sometimes in borehole water. Although they survive long periods they are more susceptible to the extremes of environmental conditions, and viability decays more rapidly than oocyst numbers.

It was not possible to link an epidemiological study with the survey of occurrence, although a retrospective study of cases of cryptosporidiosis was made.

An initial evaluation of the removal of oocysts by water treatment using bench-scale studies indicated that a well operated plant ought to achieve an overall removal of up to five logs.

The relationship between the work under this contract and other studies is discussed.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.