Early Respiratory Infections and the Development of Asthma in the First 27 Years of Life

Aino K. Rantala; Maritta S. Jaakkola; Elina M. S. Mäkikyrö; Timo T. Hugg; Jouni J. K. Jaakkola


Am J Epidemiol. 2015;182(7):615-623. 

In This Article

Abstract and Introduction


Previous studies have provided contradictory evidence on the role of early childhood respiratory infections in the development of asthma and other allergic diseases during childhood. We investigated early-life respiratory infections as predictors of the development of asthma in a 20-year prospective cohort study (the Espoo Cohort Study, 1991–2011). Information on upper respiratory tract infections (URTIs) and lower respiratory tract infections (LRTIs) was collected with a parent-administered baseline questionnaire covering the preceding 12 months (part 1; n = 2,228), and information on LRTIs leading to hospitalization was obtained from the National Hospital Discharge Registry (part 2; n = 2,568). The incidence of asthma was assessed on the basis of 6-year and 20-year follow-up questionnaires. Adjusted hazard ratios were estimated using Cox proportional hazards models. Both URTIs (adjusted hazard ratio (HR) = 1.64, 95% confidence interval (CI): 1.22, 2.19) and LRTIs (adjusted HR = 2.11, 95% CI: 1.48, 3.00) in early childhood were strong predictors of asthma incidence up to young adulthood (ages 20–27 years). A declining age trend was present for both URTIs (P-trend < 0.01) and LRTIs (P-trend < 0.001). In part 2 of our analysis, a significant risk of asthma was found in relation to LRTIs requiring hospitalization (adjusted HR = 1.93, 95% CI: 1.10, 3.38). The results provide new evidence that respiratory tract infections in early life predict the development of asthma through childhood to young adulthood.


Currently, 235–300 million people worldwide are affected by asthma, and approximately 346,000 people per year die from it.[1,2] Respiratory tract infections constitute the most common group of acute illnesses occurring during early childhood, with a median of 5 episodes of upper respiratory tract infection (URTI) per year,[3] and they remain common later in life as well. The incidence of severe acute lower respiratory tract infection (LRTI) among children in industrial countries has been estimated at 1 episode per 100 person-years.[4] Previous studies have provided contradictory evidence on the role of early childhood infections in the development of asthma and other allergic diseases during childhood; some results have been consistent with a protective effect, mainly based on indirect evidence regarding family size or day-care attendance (the original "hygiene hypothesis"),[5–9] while other researchers have reported an increased risk of asthma.[10–19] In a systematic search of the literature, we did not identify any previous population-based longitudinal studies that investigated how childhood infections predict the development of asthma up to adulthood.

The Espoo Cohort Study is a 20-year population-based prospective cohort study implemented to assess the role of early-life exposures in the development of asthma during the first 20–27 years of life. This study offered a unique opportunity to assess the relationship between early respiratory tract infections and the risk of developing asthma prospectively through childhood and up to young adulthood. In addition, we were able to link the study's data with registry-based information on early infections requiring hospitalization.