Risk factors for sporadic cryptosporidiosis were determined in 152 patients and 466 unmatched controls who resided in two local government districts in North Cumbria, North West England, from March 1, 1996, to February 29, 2000. Risk was associated with the usual daily volume of cold unboiled tap water drunk (odds ratio [OR] 1.40, 95% confidence intervals [CI] 1.14 to 1.71 per pint consumed per day [p = 0.001]) and short visits to farms (OR 2.02, 95% CI 1.04 to 3.90, p = 0.04). Fifty-six (84%) of 67 fecal specimens from patients obtained from January 1, 1998, and February 29, 2000, were Cryptosporidium parvum genotype 2 (animal and human strain). Livestock fecal pollution of water sources appears to be the leading cause of human sporadic cryptosporidiosis in this population and shows the need for better protection of water catchments from livestock and improved drinking water treatment in this area of England.

The incidence of sporadic cryptosporidiosis among 106,000 residents of 2 local government districts in northwest England before and after installation of membrane filtration of public water supplies was compared to that of 59,700 residents whose public water supplies remained unchanged. A national outbreak of foot and mouth disease in livestock during 2001 was associated with a decline in sporadic human cryptosporidiosis in all regions of the United Kingdom. In a Poisson regression model, membrane filtration was associated with an estimated 79% reduction (incidence ratio 0.207, 95% confidence intervals 0.099-0.431, p < 0.0001) after adjustment for the interval of the foot and mouth disease epidemic and the water source. Despite the confounding effect of that epidemic, membrane filtration of the public water supply was effective in reducing the risk for sporadic human Cryptosporidium infection in this population.

Sporadic cryptosporidiosis and associated hospital admissions of children declined after membrane filtration of public drinking water supplies was introduced.