TRAFFIC-RELATED NO2 AND THE PREVALENCE OF ASTHMA AND RESPIRATORY SYMPTOMS IN 7 YEAR OLDS

The aim of this study was to determine whether outdoor nitrogen dioxid e (NO2) was associated with the prevalence of asthma and respiratory s ymptoms. In eight nonurban communities, 843 children resident for a mi nimum of 2 yrs were studied. Since industrial sources of air pollution were at least 20 km away from the study communities, NO2 was consider ed to primarily indicate traffic-related air pollution. NO2 was record ed at central monitors, and the 3 yr mean exposure was calculated. Ast hma and respiratory symptoms were assessed according to the Internatio nal Study on Asthma and Allergy in Childhood. Prevalence of asthma at some time (''ever asthma'') was associated with longterm NO2. In paral lel with increasing levels of NO2 (community specific 3 yr mean 6.0-17 .0 parts per billion (ppb)), asthma prevalence was 2.5, 1.4, 1.6, 2.3, 3.4, 3.6, 7.6 and 8.5%, respectively (p=0.002 for trend). The prevale nce odds ratios (PORs) for ''ever asthma'',following adjustment for ge nder, age, parental education, passive smoke exposure, type of indoor heating, and parental asthma, were 1.28 (95% confidence interval (95% CI) 0.20-7.98), 2.14 (95% CI 0.40-11.3) and 5.81 (95% CI 1.27-26.5), w hen each of two communities with low, regular and high NO2, respective ly, were compared with the two communities with very low NO2. For symp toms ''wheeze'' (adjusted PORs for increased NO2: 1.47, 1.23 and 2.27) and ''cough apart from colds'' (adjusted PORs for increased NO2: 1.49 , 1.93 and 2.07), a similar trend was seen. In this study a significan t relationship was observed between traffic-related nitrogen dioxide a nd the prevalence of asthma and symptoms. Whether this association is causal has to be tested in longitudinal studies.