Community outbreak of adenovirus type 7a infections associated with a swimming pool

In July 1982, an outbreak of pharyngitis caused by adenovirus type 7a occurred among children in a small town in western Oklahoma. Predominant symptoms were fever and sore throat (by case definition), headache (83%), abdominal pain (64%), and conjunctivitis (51%). At least 77 persons were identified whose symptoms met the case definition for illness. Onsets of illness peaked during the week of July 5 to 12, and the outbreak resolved within three weeks. A systematic telephone survey of the town revealed that persons who had swum at the community swimming pool were more likely to be ill than those who had not (P less than .001). A second survey of families with season passes to the pool showed that among swimmers, illness was directly related to average number of hours of exposure to the pool each week (P less than .001 by chi-square for trend). In addition, swimmers who reported swallowing pool water were more likely to be ill (29 of 56, 52%) than persons who did not (ten of 41, 24%) (P = .01). Throat-swab specimens from five of seven ill persons (71%) grew adenovirus 7a compared with one of 12 well persons (8%) (P = .01). The pool chlorinator had reportedly malfunctioned during early July. The outbreak resolved with proper operation of the chlorination system. Swimming pools continue to be a potential source of community-wide outbreaks of adenovirus infections.