Longitudinal Associations between Respiratory Infections and Asthma in Young Children.

We examined temporal dependencies between repeated assessments of respiratory infections and asthma in children in the Leicester Respiratory Cohort, Leicestershire, UK. Asthma (doctor diagnosis, health care visits, wheeze frequency) and respiratory infections (cold duration and frequency, cough with colds, ear infections) in the previous 12 months were assessed repeatedly at ages 1, 4, and 6 years for children born between April 1996 and April 1997. We determined associations between contemporaneous and lagged measures of asthma and respiratory infections using structural equation modelling. In 1995 children, asthma was positively associated with contemporaneous infections. Asthma at age 6 was positively associated with asthma at age 4 (regression coefficient = 0.87; 95% CI 0.76, 0.97), but not with asthma at age 1 (-0.01; -0.14, 0.11). We found no evidence for direct protective effect of infections at age 1 on asthma either at age 4 (-0.20; -0.51, 0.10) or 6 (0.24; -0.04, 0.52). Adjusting for potential confounders did not qualitatively change those relationships. Our findings suggest that asthma at age 6 is directly influenced by asthma history and only indirectly if, at all, by earlier infection episodes. We found little support for a protective effect of preschool infections on asthma at early school age.