RESEARCH Our findings contrast with a case-control study in Adelaide and Melbourne, which did not detect increased risk for sporadic cryptosporidiosis associated with the public water supplies (29). This difference may reflect the quality of the source waters, of water treatment, or both in these cities. Swimming pool exposure was the most signif- icant risk factor in the Australian study. Regularly consum- ing raw vegetables was protective in that study. We also observed a protective association with lettuce, tomatoes, and mixed salad, and additionally for cream, in single vari- able analysis. These foods might have conferred a direct protective nutrient effect, been markers for more favorable general nutrition, or contained small numbers of oocysts derived from water used for irrigation and preparation suf- ficient to induce immune boosting (3,30,31). A recent study of sporadic cryptosporidiosis in the San Francisco Bay Area also failed to show an association with tap water, but the study was small (32). Most of our patients were children, which suggests that older members of our study population were mainly immune, probably because of long-term immune boosting from low-level intermittent contamination of water sup- plies and contact with livestock (31,33). This observation is consistent with recent seroprevalence studies in blood donors resident in midwestern American cities and indi- cates lower seroprevalence of Cryptosporidium antibodies in populations served by deep borehole water compared to lake and river water supplies (34,35). No association was seen for contact with pets at home, pets with diarrhea, or feeding tinned pet meat, raw meat, or pellets. However, feeding pets biscuits and raw vegetables was associated with slightly increased risk in single vari- able analysis and in the final multivariable model. These food types may be markers for more intimate contact with animal secretions; feeding raw vegetables may indicate contact with contaminated water in preparation. Although contamination of pet biscuits is possible, these products are dry and manufactured at high temperature; thus, sur- vival of oocysts within these foods seems unlikely. Accidental hand contact with the feces of any type of ani- mal was significant in single variable analysis but not in the final multivariable model. These results suggest that sound hygiene in cleaning animal feeding utensils, avoid- ing cross-contamination between pet and human food preparation areas, and good hand hygiene are desirable but that pets and pet feeding were not major risk factors for cryptosporidiosis in this population. The findings of this study are consistent with the decline in human Cryptosporidium infection throughout England and Wales, coincident with the foot and mouth disease epidemic in livestock during 2001 (13). These two facts strongly suggest that livestock reservoirs of Cryptosporidium contribute substantially to sporadic human cryptosporidiosis in North Cumbria and in England and Wales as a whole, through low-level intermittent Cryptosporidium oocyst contamination of public drinking water supplies. Our results support the need for rigorous risk assessment of water sources and, where indicated, improved catchment control. Our results are also in accord with recent U.K. legislation that requires continuous mon- itoring of Cryptosporidium oocyst concentrations in treat- ed water from at-risk supplies (36). Advanced methods of filtration, disinfection, and UV light treatment may be required to further decrease the risk for cryptosporidiosis from public water supplies (5,37,38). The water company installed membrane filtration dur- ing 2000 at works served by Crummock and Ennerdale Lakes, which previously provided chlorination alone. The impact of this intervention will be presented in a separate article. Acknowledgments We thank colleagues in the Steering Group and in the many local and national agencies that contributed to this research, in particular, Brian White, Vic Emmerson, Mary Cosgrove, Peter Daley, John Cain, Rachel Horton, Susan Partridge, Judith Hilton, Patrick Wall, Ros Stanwell-Smith, James Stuart, Claire Gilham, Alan Godfree, Matthew Wilkinson, Charmian Kerr, David Counter, Andrew Holliman, John Gray, Tony Lloyd, Mark Smith, David Holt, Joy Graham, Jennifer Clay, Paul Blaylock, Richard Lamb, Dennis Massey, Emma Wigginton, Anthony Pennington, Kristin Elwin, and Anne Thomas. This study was funded by the Department of Environment, Food and Rural Affairs, Department of Health, United Kingdom Water Industry Research Limited, and was supervised by the Drinking Water Inspectorate. Dr. Goh is an honorary consultant to the Carlisle and District Primary Care Trust and was formerly the consultant in Communicable Disease Control to North Cumbria Health Authority, in North West England. She specialized in public health medicine and developed an interest in childhood immu- nization, enteric infection, Cryptosporidium, and water supplies. References 1. Fayer R, Morgan U, Upton SJ. Epidemiology of Cryptosporidium: transmission, detection, and identification. Int J Parasitol. 2000;30:1305–22. 2. Guerrant RL. Cryptosporidiosis: an emerging highly infectious threat. Emerg Infect Dis. 1997;3:51–57. 3. Kosek M, Alcantara A, Lima AAM, Guerrant RL. Cryptosporidiosis: an update. Lancet. Infect Dis 2001;1:262–9. 4. Meinhardt PL, Casemore DP, Miller KB. Epidemiological aspects of human cryptosporidiosis and the role of waterborne transmission. Epidemiol Rev. 1996;18:118–36. 1014 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004