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BACKGROUND: A population-based case-control study was performed in Stockholm to assess the influence of air pollution on the occurrence of severe wheezing bronchitis in children. METHODS: The study included 197 children aged 4 months to 4 years, who were hospitalized because of breathing difficulties with wheezing, and 350 population controls. Information on potential risk factors for childhood wheezing and a residential history was obtained at home interview with parents. Outdoor nitrogen dioxide (NO2) concentrations at home addresses and day care centres from birth on were estimated from validated models, mainly using data on traffic intensity from municipal registers. RESULTS: The risk of wheezing bronchitis was related to time-weighted mean outdoor NO2 exposure in girls (P = 0.02), but not in boys. A gas stove in the home appeared to be a risk factor primarily for girls. All analyses controlled for parental asthma and maternal smoking, which were independent risk factors for wheezing bronchitis. CONCLUSIONS: The results suggest that exposure to combustion products containing NO2 may be of particular importance for the development of wheezing bronchitis in girls.
Pershagen et al. (Sun,) studied this question.