NO(2), as a marker of air pollution, and recurrent wheezing in children: a nested case-control study within the BAMSE birth cohort

Aims: To investigate the association between air pollution, including with NO(2), and recurrent wheezing during the first two years of life. Methods: A birth cohort (BAMSE) comprised 4089 children, for whom information on exposures, symptoms, and diseases was available from parental questionnaires at ages 2 months, and 1 and 2 years. NO(2) was measured during four weeks in and outside the dwellings of children with recurrent wheezing and two age matched controls, in a nested case-control study (540 children). Results: Conditional logistic regression showed an OR of 1.60 (95% CI 0.78 to 3.26) among children in the highest quartile of outdoor NO(2) exposure in relation to those in the lowest quartile, adjusted for potential confounders. The corresponding OR for indoor NO(2) was 1.51 (95% CI 0.81 to 2.82). An interaction with environmental tobacco smoke (ETS) was indicated with an OR of 3.10 (95% CI 1.32 to 7.30) among children exposed to the highest quartile of indoor NO(2) and ETS. The association between NO(2) and recurrent wheezing appeared stronger in children who did not fulfil the criteria for recurrent wheezing until their second year. Conclusions: Although the odds of increased recurrent wheezing are not statistically significantly different from one, results suggest that exposure to air pollution including NO(2), particularly in combination with exposure to ETS, increases the risk of recurrent wheezing in children