Blood eosinophils during bronchiolitis: Associations with atopy, asthma and lung function in young adults

Abstract Aim To study if blood eosinophils during bronchiolitis were associated with atopy, asthma and lung function in young adults and if these associations differed between respiratory syncytial virus (RSV) bronchiolitis and non‐RSV bronchiolitis. Methods This historical cohort enrolled 225 subjects. Blood eosinophils were measured during bronchiolitis in infancy, and the subjects were invited to a follow‐up at 17–20 years of age including questionnaires for asthma and examinations of lung function and atopy. Results The level of eosinophils was positively associated with subsequent atopy in the unadjusted analysis, but not in the adjusted analysis, and not with asthma. There was a negative association between the level of eosinophils and forced vital capacity (FVC) (−0.11; −0.19, −0.02) and forced expiratory volume in first second (FEV1) (−0.12; −0.21, −0.03) (regression coefficient; 95% confidence interval). The non‐RSV group had higher levels of eosinophils during bronchiolitis, but there was no interaction between the level of eosinophils and RSV status for any outcome. Conclusions The level of eosinophils during bronchiolitis was negatively associated with lung function in young adult age, but we found no associations with atopy or asthma. These associations were not different after RSV bronchiolitis compared to non‐RSV bronchiolitis.