Determinants of asthma after severe respiratory syncytial virus bronchiolitis

Background: The development of asthma after respiratory syncytial virus (RSV) bronchiolitis has been demonstrated in case-control studies, although the determinants of post-RSV asthma remain undefined. Objectives: We sought to evaluate the potential determinants of physician-diagnosed asthma after severe RSV bronchiolitis during infancy. Methods: We enrolled 206 children during an initial episode of severe RSV bronchiolitis at 12 months of age or less in a prospective cohort study and followed these children for up to 6 years. In a subset of 81 children, we analyzed CCL5 (RANTES) mRNA expression in upper airway epithelial cells. Results: Forty-eight percent of children had physician-diagnosed asthma before the seventh birthday. Independent determinants significantly associated with increased risk for physician-diagnosed asthma by the seventh birthday included maternal asthma (odds ratio [OR], 5.2; 95% CI, 1.7-15.9; P =.004), exposure to high levels of dog allergen (OR, 3.2; 95% CI, 1.3-7.7; P =.012), aeroallergen sensitivity at age 3 years (OR, 10.7; 95% CI, 2.1-55.0; P =.005), recurrent wheezing during the first 3 years of life (OR, 7.3; 95% CI, 1.2-43.3; P =.028), and CCL5 expression in nasal epithelia during acute RSV infection (OR, 3.8; 95% CI, 1.2-2.4; P <.001). White children (OR, 0.19; 95% CI, 0.04-0.93; P =.041) and children attending day care (OR, 0.18; 95% CI, 0.04-0.84; P =.029) had a decreased risk of physician-diagnosed asthma. Conclusions: Approximately 50% of children who experience severe RSV bronchiolitis have a subsequent asthma diagnosis. The presence of increased CCL5 levels in nasal epithelia at the time of bronchiolitis or the development of allergic sensitization by age 3 years are associated with increased likelihood of subsequent asthma.