Outdoor sulphur dioxide and respiratory symptoms in Czech and Polish school children: a small-area study (SAVIAH)

Objectives: Air pollution has been linked to respiratory outcomes but controversy persists about its long-term effects. We used a novel technique to estimate the outdoor concentrations of sulphur dioxide (SO2) at small-area level to study the long-term effects on respiratory symptoms and disease in children. Methods: As part of the international SAVIAH study, parents of 8,013 children aged 7-10 studied in Prague (Czech Republic) and Poznan (Poland) completed a questionnaire covering respiratory health, demographic and socio-economic factors and health behaviours (response rate 91%). This report is based on 6,959 children with complete data. Outdoor SO2 was measured by passive samplers at 80 sites in Poznan and 50 sites in Prague during 2-week campaigns. Concentrations Of SO2 at each point (location) in the study areas were estimated from these data by modelling in a geographical information system. The mean ofthe estimated SO2 concentrations at children's homes and schools was used as an indicator of exposure to outdoor SO2. Results: The prevalence of respiratory outcomes was similar in both cities. In the pooled data, 12% of children had experienced wheezing/whistling in the past 12 months; 28% had a lifetime prevalence of wheezing/whistling; 14% had a dry cough at night; and 3% had had asthma diagnosed by a doctor. The estimated mean exposure to outdoor SO, was 80 (range 44-140) mug/m(3) in Poznan and 84 (66-97) mug/m(3) in Prague. After socio-economic characteristics and other covariates were controlled for, SO2 was associated with wheezing/whistling in the past 12 months (adjusted OR per 50 mug/m(3) 1.32, 95% Cl 1.10-1.57), lifetime prevalence of wheezing/whistling (OR 1.13, 95% CI 0.99-1.30), and lifetime prevalence of asthma diagnosed by a doctor (OR 1.39, 95% Cl 1.01-1.92). The association with dry cough at night did not reach statistical significance. Conclusions: In these two Central European cities with relatively high levels of air pollution, small-area based indicators of long-term outdoor winter concentrations Of SO2 were associated with wheezing / whistling and with asthma diagnosed by a doctor.