Adenovirus Type 3 Epidemic Associated with Intermittent Chlorination of a Swimming Pool

A sharp outbreak of pharyngoconjunctival fever due to adenovirus type 3 occurred in two swimming teams shortly alter exposure to unchlorinated water. Children swimming in the chlorinated water suffered no similar illness. The attack rate was 65% and 67% for each team, Attempts to isolate the virus from the water after the outbreak failed. In ten of 19 affected families, transmission to other family members was demonstrated; the secondary attack rate for children was 63%, for adults 19%. The majority of infected children suffered fever, pharyngitis, and conjunctivitis; symptoms in adults were milder, with conjunctivitis predominating. Diarrhea was more common among children infected at home. The median incubation period for swimmers was estimated at seven days; the median case-to-case interval in the families was 11 days.