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Maternal smoking, asthma, and bronchiolitis: clear-cut association or equivocal evidence?

Article Excerpt
Although there is no doubt that secondhand environmental tobacco smoke exposure contributes to lower respiratory tract infection (LRTI) in infants and young children in developing countries (1) and industrialized nations, (2,3) the evidence for a specific effect on respiratory syncytial virus (RSV) LRTI is less clear. (4) It is the equivocal nature of the evidence for the role of smoking affecting the severity of RSV bronchiolitis that has, in part, prevented the American Academy of Pediatrics from strongly advocating smoking as a risk factor when considering prophylaxis with palivizumab for previously premature infants of 32 to 35 weeks' gestation. (5-7)

In this issue of Pediatrics, Carroll et al (8) present probably the largest population-based study of term infants with bronchiolitis to determine the association between maternal asthma, maternal smoking, and the incidence and severity of bronchiolitis. In their cohort of > 100 000 mother-infant dyads, >20% of the infants had 1 health care visit for bronchiolitis. Maternal smoking increased the risk of bronchiolitis by 14%, maternal asthma raised it by 39%, and both together raised it by 47%. Infants of mothers with asthma who smoked had a higher risk for emergency department visits and hospitalizations. Although maternal smoking increased the risk of prolonged hospitalization by 19%, if the mother was smoking and had asthma the increased risk was 38%. Given the enormous size of the study encompassing the vast majority of children, infants, and mothers enrolled in the Tennessee Medicaid program between 1995 and 2003, this would seem to be compelling evidence for an association between maternal smoking and bronchiolitis.

Despite the enormous size of this study, the results must be tempered with an understanding of the study limitations, which were acknowledged by the authors. The major limitation is that other risk factors that...

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