Background
Early life respiratory tract infections have been linked to the development of asthma, but studies on the burden and subtypes of common infections in asthma development are sparse.

Objective
To examine the association between burden of early life infections, including subtypes, with the risk of asthma from age 3 to 10 years and lung function at age 10 years.

Methods
We included 662 children from the Copenhagen Prospective Studies on Asthma in Childhood 2010 birth cohort, for whom infections such as colds, acute tonsillitis, acute otitis media, pneumonia, gastroenteritis, and fever were registered prospectively in daily diaries at age 0 to 3 years and asthma was diagnosed longitudinally from age 3 to 10 years. The association between the burden of infection and subtypes and risk of asthma was analyzed by generalized estimating equations.

Results
The children experienced a median of 16 infections (interquartile range, 12-23 infections) at age 0 to 3 years. Children with a high burden of infections (above the median) had an increased risk of asthma at age 3 to 10 years (adjusted odds ratio = 3.61; 95% CI, 2.39-5.45; P < .001), which was driven by colds, pneumonia, gastroenteritis, and fever episodes (P < .05) but not by acute otitis media and tonsillitis. Lower lung function measures at age 10 years were associated with the burden of pneumonia but not the overall infection burden. The association between colds and the risk of asthma was significantly higher in children with allergic rhinitis at age 6 years (P interaction = .032).

Conclusion
A high burden of early life infections in terms of colds, pneumonia, gastroenteritis, and fever is associated with an increased risk of developing asthma, particularly in children with respiratory allergy. Strategies to diminish these early life infections may offer a path for the primary prevention of childhood asthma.