A statewide outbreak of cryptosporidiosis in New South Wales associated with swimming at public pools

From December 1997 to April 1998, 1060 laboratory-confirmed cryptosporidios is cases were reported in New South Wales, Australia. In a case-control stu dy, compared with 200 controls, the 100 cases were younger (mean age 4(.)2 versus 7(.)1 years; P < 0(.)0001), more likely to report swimming at a publ ic pool (59% versus 38%; adjusted OR and 95% CI = 2(.)7; 1(.)4-5(.)1) and s wimming in a dam, river or lake (OR = 4(.)8; 1(.)1-20(.)3) but less likely to report drinking bottled water (OR = 0(.)4; 0(.)2-0(.)9). In subgroup ana lyses, in rural areas illness was associated mainly with contact with anoth er person with diarrhoea, and in urban areas illness was associated with sw imming in a public pool. Cryptosporidium oocysts were more commonly detecte d in pools to which at least two notified cases had swum (P = 0(.)04). Outb reaks of cryptosporidiosis can be prolonged, involve multiple pools and be difficult to control.