The severity-dependent relationship of infant bronchiolitis on the risk and morbidity of early childhood asthma

Background: Infants hospitalized for bronchiolitis have a high rate of early childhood asthma. It is not known whether bronchiolitis severity correlates with the risk of early childhood asthma or with asthma-specific morbidity. Objectives: We sought to determine whether a dose-response relationship exists between severity of infant bronchiolitis and both the odds of early childhood asthma and asthma-specific morbidity. Methods: We conducted a population-based retrospective birth cohort study of term healthy infants born from 1995-2000 and enrolled in a statewide Medicaid program. We defined bronchiolitis severity by categorizing infants into mutually exclusive groups based on the most advanced level of health care for bronchiolitis. Health care visits, asthma-specific medications, and demographics were identified entirely from Medicaid and linked vital records files. Asthma was ascertained at between 4 and 5.5 years of age, and 1-year asthma morbidity (hospitalization, emergency department visit, or oral corticosteroid course) was determined between 4.5 and 5.5 years among children with prevalent asthma. Results: Among 90,341 children, 18% had an infant bronchiolitis visit, and these infants contributed to 31% of early childhood asthma diagnoses. Relative to children with no infant bronchiolitis visit, the adjusted odds ratios for asthma were 1.86 (95% CI, 1.74-1.99), 2.41 (95% CI, 2.21-2.62), and 2.82 (95% CI, 2.61-3.03) in the outpatient, emergency department, and hospitalization groups, respectively. Children hospitalized with bronchiolitis during infancy had increased early childhood asthma morbidity compared with that seen in children with no bronchiolitis visit. Conclusion: To our knowledge, this is the first study to demonstrate the dose-response relationship between the severity of infant bronchiolitis and the increased odds of both early childhood asthma and asthma-specific morbidity. (J Allergy Clin Immunol 2009;123:1055-61.)