Early-life respiratory tract infections and the risk of lower lung function and asthma: a meta-analysis of 154,492 children

Background Early-life respiratory tract infections could affect airway obstruction and increase the risk of asthma in later life. Objective We examined the associations of early-life respiratory tract infections with lung function and asthma in children. Methods We used individual participant data of 154,492 children from 37 birth cohorts to examine the associations of upper (URTI) and lower respiratory tract infections (LRTI) by the age of 6 months, 1, 2, 3, 4 and 5 years with forced expiratory volume in 1 second (FEV 1 ), forced vital capacity (FVC) FEV 1 /FVC, forced expiratory flow at 75% of FVC (FEF 75 ) and asthma at a mean age of 7 (SD 2) years. We used multilevel mixed effect models, to take clustering of participants within cohorts into account, and adjusted for socio-economic, lifestyle and growth factors. Results URTI were not associated with lung function. URTI at all ages were associated with an increased risk of asthma (OR (95% CI): ranging from 1.25 (1.15, 1.34) to 1.56 (1.47, 1.66)). LRTI at all ages were associated with a lower FEV 1 , FEV 1 /FVC and FEF 75 (Z-score (95% CI): ranging from -0.07 (-0.14, -0.00) to -0.24 (-0.38, -0.10)), except for LRTI at age 6 months with FEF 75 , and an increased risk of asthma (OR (95% CI): ranging from 2.00 (1.85, 2.10) to 3.72 (3.19, 3.85)). Conclusion Early-life lower respiratory tract infections are associated with lower lung function and increased risk of asthma in later life, while upper respiratory tract infections are associated with asthma only. These findings support the hypothesis that early-life respiratory tract infections might affect long term respiratory morbidity.