Our study shows that bronchiolitis care episodes were frequent during the first two years of life in this study cohort and that, consistent with prior research, most occurred outside the hospital setting. In our large cohort, the duration of bronchiolitis episodes ranged from 1 to 27 days. Among episodes with duration >1 day, the mean duration was 7.0 ± 5.9 days, potentially indicating significant morbidity for this subset of infants. Preterm infants compared to full-term infants had higher overall bronchiolitis episode rates as well as higher rates of episodes with an ED and/or inpatient hospital admission during the first two years of life, which might reflect both an intrinsically higher risk of morbidity in this population and/or an increased level of parent and provider concern regarding their medical needs. In addition to prematurity, male gender, neonatal oxygen use, family history of asthma, and African-American or Hispanic race/ethnicity were associated with a higher frequency of at least one episode and/or a higher frequency of an episode >1 day.
Consistent with previous studies, the overall burden of disease in this population was relatively high, with 16.2% of children in this study having a documented episode of bronchiolitis before age two. An episode of care approach in characterizing the utilization patterns of infants and children with bronchiolitis may be useful for health services researchers, physicians, and parents in understanding a broader healthcare burden of disease. Analyzing episodes of care may be more informative than reporting the rates of discrete bronchiolitis-related medical encounters.
Our study has several important limitations. First, not all infants with bronchiolitis seek medical care. This study reports frequency and associated characteristics of bronchiolitis that led to a clinical encounter, but is not a prospective study of the entire burden of illness from bronchiolitis that includes patient reports of symptoms . Nevertheless, the study design provided a good approximation of the total health care utilization associated with bronchiolitis. Second, we ascertained bronchiolitis diagnoses using ICD-9 codes. To be considered an episode, a subject needed to have ≥1 diagnostic code specific for bronchiolitis or viral pneumonia attributable to pathogens typically causing bronchiolitis (Category A). Because bronchiolitis is a clinical diagnosis, it is possible that some cases of bronchiolitis were instead coded as “fever,” “wheeze,” or “lower respiratory infection.”However, it is also possible that some pneumonia attributed to pathogens typically causing bronchiolitis was not in fact bronchiolitis, and that some episodes of asthma, viral pneumonia or upper respiratory infection were coded as “bronchiolitis.” Therefore, it is likely that the total error from miscoding of bronchiolitis is relatively small. Third, we estimated membership based on a combination of membership and use status in each cohort month. Because infants with a higher level of use might tend to have higher frequency of seeking medical care, it is possible that this might bias the results towards higher estimates of bronchiolitis episodes. Since the sensitivity analysis including only infants with 24 months of documented membership did not show much difference from the primary analysis, the effect of membership status is likely to be minimal. Fourth, there were no reliable data on smoking for this analysis. Because smoking in the home is a major predictor of bronchiolitis episodes and because maternal smoking is associated with preterm birth and with race/ethnicity, it is possible that smoking might confound the relationship between GA and incidence of bronchiolitis. However, in our previous work we have found that the overall rate of smoking among mothers delivering at KPMCP is 4%–8% . Therefore, we do not believe this has had a large impact on our results. Fifth, because rates of episodes and episodes with hospitalization might be impacted by participation in an integrated healthcare delivery system, it is possible that our results may not be generalizable to other healthcare systems. However, because the KPMCP provides medical care to a large portion of infants born in Northern California, our data represent an important estimate of overall care episodes in this population. Sixth, our data on race/ethnicity include only the categories White, African-American, Asian, Hispanic and other, and we do not have access to more detailed data. Therefore, we cannot report how more specific subgroups of race/ethnicity might alter bronchiolitis risk.
Despite these limitations, our research design offers the unique opportunity to study an entire birth cohort using linked data with relatively little loss to follow-up and to report the health care utilization related to bronchiolitis in this prospective cohort. Thus, we are able to provide a comprehensive description of burden of disease in this population, including frequency and severity of illness. In addition, the large sample size of our cohort has allowed us to identify many predictors associated with the disease outcome, which include gestational age, race/ethnicity, maternal age, small for GA, presence of congenital anomaly, family history of asthma, at least one sibling <5 years of age in the home, and degree of oxygen exposure or having BPD.