Early-life Respiratory Tract Infections and the Risk of School-age Lower Lung Function and Asthma: a Meta-analysis of 150 000 European Children

To examine the associations of early-life upper and lower respiratory tract infections with lung function and asthma at school age.

Study population included 150 090 children born between 1989 and 2013 from 38 European birth cohorts with available relevant data on early respiratory tract infections and childhood lung function and/or asthma.

Investigators collected information on respiratory tract infections in the last 6 or 12 months at serial ages, from 6 months to 5 years of age. Efforts were made to use physician-diagnosed infections, which were then classified as either “upper” or “lower” tract infections. The main respiratory outcomes were lung function measured by spirometry and physician-diagnosed asthma. Healthcare registry data, interviews, and symptom diaries were also used to obtain information on asthma.

Upper and lower respiratory tract infections in early childhood were associated with an increased risk of asthma, with an odds ratio of 1.25 to 1.57 and 2.10 to 6.30, respectively. Lower respiratory tract infections at all ages were also associated with lower forced expiratory volume 1 and forced expiratory volume 1/forced vital capacity ratio. These results did not change when accounting for wheezing in early childhood, though the strengths of association decreased slightly when adjusting for preceding respiratory infections.

Early-life upper respiratory infections were associated with an increased risk of school-age asthma. Early-life lower respiratory infections were associated with lower lung function at school age and an even stronger risk of asthma.

This study adds to the growing body of evidence that early life infections, particularly in the lower respiratory tract, can impact the development of asthma. Previous studies have focused on specific viral pathogens (eg, rhinovirus or respiratory syncytial virus), however this study suggests that other respiratory infections, even when mild, may impact the immune system enough to drive the development of a chronic disease, such as asthma. This study is limited by the absence of objective lung function measurements in the majority of the studied population, as well as lack of bronchodilator reversibility and testing pre and post infection. Since only 17% of the cohort even had pulmonary function testing completed, future research efforts could aim for a more substantial capture of lung function measurements to follow both the clinical and measurable consequences of viral respiratory infections.