Prenatal and postnatal tobacco smoke exposure and risk of severe bronchiolitis during infancy

Background: Maternal prenatal smoking has adverse effects on the growing fetus including those of respiratory nature. Although postnatal smoke exposure is a risk factor for respiratory infections, the effects of prenatal smoking independent of postnatal smoke exposure are less established. We hypothesized that both maternal prenatal smoking, and postnatal smoke exposure are risk factors for severe bronchiolitis during infancy. Methods: We performed a case-control study of 1353 children born between 1996 and 2011 at a single teaching hospital. Cases were admitted to the same hospital for bronchiolitis during infancy. Maternal prenatal smoking was collected from birth records. Postnatal smoke exposure was collected from review of electronic health records. Multivariable logistic regression was used to evaluate the independent associations of the two smoking variables with severe bronchiolitis. Results: 6% of cases were exposed to maternal prenatal smoking, compared with 4% of controls (P=0.10). Postnatal smoke exposure was present in the households of 17% of cases compared with 3% of controls (P < 0.001). In a multivariable model with both smoking variables and adjustment for 10 covariates, maternal prenatal smoking was not a significant risk factor for severe bronchiolitis (adjusted OR=1.02, 95% CI 0.56-1.84). By contrast, postnatal smoke exposure was associated with > 300% increased odds (adjusted OR 4.19, 95% CI 2.51-6.98). Conclusions: Although maternal prenatal smoking has many known adverse effects, it was not associated with increased odds of severe bronchiolitis in either unadjusted or multivariable analyses. Postnatal smoke exposure was a consistently strong risk factor. Our findings support ongoing efforts to decrease infant exposure to ambient smoke.