Croup in infancy and subsequent asthma development: is there a link?

Croup is a common respiratory illness in young children and usually resolves spontaneously. This study investigated whether a history of croup is associated with an increased risk of childhood asthma.

Using the Korean National Health Insurance Service database, we conducted a nationwide, population-based cohort study of children born between 2008 and 2012. Children treated for croup in an emergency department were assigned to the exposed group, and 10 age- and sex-matched children without croup were selected as controls for each case. Asthma was defined based on diagnostic codes, asthma-related medications, or asthma-related hospitalization, and asthma incidence was followed through 2021. Associations between croup and subsequent asthma were assessed using Cox proportional hazards models adjusted for demographic and perinatal factors.

The cohort included 10,879 children with croup and 108,790 matched controls. The incidence of asthma was slightly higher in the croup group than in controls (41.8 vs. 38.6 per 1000 person-years). A history of croup was associated with a modestly increased risk of asthma (adjusted hazard ratio (aHR), 1.07; 95% confidence interval (CI), 1.02-1.13). Recurrent croup (≥2 episodes) was associated with a substantially higher asthma risk (aHR 1.41, 95% CI, 1.27-1.56), whereas a single episode was not. The association was most pronounced among children with concomitant atopic conditions.

Recurrent croup, but not a single episode, was associated with an increased risk of subsequent asthma, suggesting that recurrent croup may be an early clinical marker of asthma susceptibility, particularly in children with coexisting atopic conditions.