There are many large and small public outdoor and indoor swimming pools in Tehran that hundreds of people use, especially on hot summer days. The bacteriological quality of the water of some of these pools was assayed over a period of about one year (2001-2002). To assess if these swimming pools were a health risk to users, eleven public swimming pools, in the east and northeast of the city, were examined, and the exposed people were monitored. Samples of swimming-pool waters were examined for colony counts, Escherichia coli and coliforms. In addition, Pseudomonas aeruginosa was isolated from nine (81.8%) of those pools. P. aeruginosa grew in seven (63.6%) of the swimming-pool water samples. In two (18.2%) other samples, in addition to P. aeruginosa, high rates of total bacterial count, total coliforms and faecal coliform counts were also found. At the same time, users of the swimming pools were asked to complete a questionnaire. Ear swabs were collected from 179 users with a history of ear problems during the previous two weeks. An adequate control group was chosen randomly from those who never used the investigated pools. P. aeruginosa was isolated from the ear swabs of 142 (79.3%) of the cases, as well as from 4% of the controls. Results were matched for age, sex, duration of time spent in the pools, place of occurrence and other useful information. Investigation of the contaminated swimming pools revealed that chlorination was often inadequate, especially when high numbers of people led to overuse of the pools. Although the results of this research showed that otitis externa was strongly associated with the swimming pools, due to P. aeruginosa, an extensive follow-up study is needed to determine the other possible health risks associated with public pools.

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