Attendance at chlorinated indoor pools and risk of asthma in adult recreational swimmers.

To study a potential correlation between attendance at chlorinated indoor pools and the onset of asthma in adult leisure swimmers. 1136 adult swimmers attending indoor pools in the city of Verona completed a modified ECRHS questionnaire. The cumulative time spent in the pools was calculated on the basis of the mean frequency and duration of weekly swim activity for every year of attendance. The median value (320 h) was used to divide participants into 2 groups. Other questions concerned the family history of allergies, the medical diagnosis and the onset of asthma. The prevalence of respiratory symptoms in the study group was compared with that of a general population sample. New-onset asthma, first identified at least 12 months after the start of regular pool attendance, was more prevalent among swimmers characterized by a higher cumulative pool attendance (23/514, 4.5%) than in swimmers who were attending indoor pools less frequently (2/508, 0.4%; ratio 11.1, 95% CI 2.6-47.4). The statistical analysis revealed an independent association between the cumulative lifetime hours spent in indoor swimming pools and new onset asthma (relative risk 1.05, 95% CI 1.02-1.07). Respiratory symptoms were less frequent in the study population versus a general population sample (prevalence ratio 0.26-0.68). Attendance at chlorinated indoor pools may constitute a risk factor for developing asthma in leisure adult swimmers. Future research and efforts should aim at improving disinfection techniques, hygiene and ventilation in indoor swimming pools in order to provide an unobjectionable ambient for salubrious swim activities.