An outbreak of cryptosporidiosis associated with exposure to swimming pool water.

An outbreak of cryptosporidiosis among visitors to a public swimming pool occurred in the late summer of 2002. We performed a retrospective cohort study, including 3 cohorts, A) 178 school-children who visited the pool on a single occasion, B) 263 arbitrarily chosen school children, aged 6-12 y, and their household members, living within the municipality where the outbreak occurred, and C) an additional 28 individuals with laboratory confirmed cryptosporidiosis. The outbreak lasted 4 weeks and affected an estimated 800-1000 individuals. The primary attack rate was 40-50%. The median incubation period was 5 d (range 2-13 d). The secondary attack rate was 8-10%. Diarrhoea was reported by 93% of the patients, abdominal pain 89%, nausea 73%, and fever 40%. Fifty-four percent had<5 loose stools and 20% had>10 loose stools per d. The duration of symptoms was 4-10 d for 52% and>10 d for 34% of the cases. This is the first reported outbreak of pool associated cryptosporidiosis in Sweden and emphasizes the importance of proper control routines of swimming pools with continuous assessment of the quality of the water sources and filtration processes.