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

Abstract

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 of the 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 SO₂ was 80 (range 44–140) µg/m³ in Poznan and 84 (66–97) µg/m³ 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 µg/m³ 1.32, 95% CI 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% CI 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.