Relationship of secondhand smoke and infant lower respiratory tract infection severity by familial atopy status

Abstract

Background: Individuals with atopy have more severe complications of infectious diseases. We hypothesized that the importance of secondhand smoke (SHS) on lower respiratory tract infection (LRTI) severity would be greater in infants with a familial atopic predisposition.

Objective: To determine whether infants with a familial atopic predisposition are more susceptible to adverse effects of SHS, resulting in more severe LRTI.

Methods: We conducted cross-sectional analyses of mother-infant dyads enrolled during 2004 to 2008 during an infant LRTI. Predictor variables were SHS and 2 measures of a familial atopic predisposition (maternal atopic disease with allergen sensitization or familial atopy). LRTI severity was determined by bronchiolitis severity score (BSS) and hospital length of stay (LOS). We conducted multivariable regression analysis to test for a differential relationship between SHS and LRTI severity by measures of familial atopic predisposition.

Results: In 451 dyads, 57% of infants had SHS exposure, 36% had a mother with atopic disease, and 68% had familial atopy. We did not detect differences in BSS or LOS by SHS exposure stratified by history of maternal atopic disease. In bivariate analysis, there was a significant difference in LOS by SHS in those with familial atopy (P = .006) but not in those without (P = .66). In multivariable analysis, among infants with familial atopy, there was a 23% increased LOS in infants with SHS exposure (P = .03), whereas no statistical significance was detected in those without familial atopy (P = .07).

Conclusion: In infants with familial atopy, SHS was associated with longer hospital LOS for LRTI but not BSS. Because the effect was seen only among hospitalized infants, confirmation is required.