Sporadic Cryptosporidiosis, England, 1996–2000 Cases 152 Controls 466 Adjusted OR CI p value 236 230 103 49 101 43 54 41 5 6 3 1 51 9 57 391 20 446 39 427 322 139 19 417 29 407 1.1 1 0.99/y 1 1.28 0.95 0.9 1.04 1.36 1.37 0.89 1.83 0.002 0.77 0.004 1.40/pint 2.02 1 2.11 1 1.77 1 1.49 1 1.96 1 1.67 1 0.73 to 1.67 0.97 to 1.01 0.61 to 2.67 0.51 to 1.78 0.39 to 2.09 0.51 to 2.13 0.61 to 3.05 0.26 to 7.11 0.16 to 4.85 0.16 to 20.37 0 to ∞ 0.34 to 1.77 0 to 203.4 1.14 to 1.71 1.04 to 3.9 0.98 to 4.56 0.94 to 3.33 0.91 to 2.43 0.79 to 4.88 0.73 to 3.82 0.64 0.29 0.71 0.001 0.04 0.06 0.08 0.1 0.15 0.23 Table 4. Final multivariable modela Variables Total Sex M F Age Water supply zones Crummock North Crummock South Ennerdale North Ennerdale South Millom Quarry Hill Hausegill Hayknott Underscar Fellside Mixed from >1 zone Private water supplies Usual daily volume of cold unboiled tap water drunkb Any short visit to a farm Y N Fed pet raw vegetables Y N Fed pet biscuits Y N Ate nonlocally produced cheese Y N Contact with farms without cattle or sheep Y N Contact with a cattle farm Y N aOR, odds ratio; CI, confidence interval. bAt home and away from home in the Allerdale/Copeland area. 82 70 37 19 29 13 19 16 3 2 1 0 11 2 40 107 13 139 21 131 113 34 15 125 15 125 coverage indicated little knowledge about risk factors for cryptosporidiosis by patients or controls. Patients may have increased fluid consumption after the onset of illness. Study participants were therefore asked to report their “usual consumption” of unboiled tap water, bottled water, and soft drinks, without a time restriction. Although a bias towards a patient’s recalling consumption of fluids after onset of illness could explain some of the association with tap water that we observed, we do not think it can explain it entirely. In particular, fluid volumes were measured in the same way for unboiled tap water, bottled water, and soft drinks, but the highly significant association and dose- response relationship were observed only for unboiled tap water. An interview date bias was avoided because patients and associated controls were enrolled within a short time of each other. Cryptosporidiosis in HIV-infected persons is associated with consuming unboiled tap water. We do not believe that undetected HIV infection or other causes of immune sup- pression could have been a major confounding factor. Only two new cases of HIV infection would be expected in Allerdale and Copeland each year even if rates for the whole North West of England were applied to the study population. However, our findings reinforce the need for immune-compromised persons, including those with HIV infection, to avoid drinking unboiled tap water (26,27). Allerdale and Copeland had very similar levels of social deprivation (28). Moreover, controls resided in approxi- mately the same locality as patients, as defined by shared lead characters of the postal code. Therefore, a systematic difference in social deprivation between patients and con- trols was unlikely and would not have explained the asso- ciations we observed. The spring peak and smaller autumn peak in our cases are consistent with previous reports from England and Wales. These peaks are attributed to lambing, calving, and runoff from spring rains and to summer travel to countries with higher incidence of cryptosporidiosis (4,13). Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004 1013