Supplementary Material for: Multiple Childhood Respiratory Viral Infections are Associated with Allergy in Young Adults

Introduction: Early-life viral infections have been linked to both increased and a decreased risk for allergic disease later in life. Causative relationships have been difficult to prove and most likely both timing and type of infection(s) are of importance. The aim was to study the association between early-life viral infections and allergy at 20 years of age. In addition, to study how early viral infections are associated with other known risk factors for allergy.
Methods: A cohort of 281 individuals recruited before birth and categorized into three hereditary groups based on parental allergy status, defined by IgE-sensitized and allergic symptoms, was followed until age 20. Of these, 142 individuals completed both web-based questionnaires and clinical investigations. Infections were documented both as parent-reported between 0-2 years and seropositivity against 13 viruses at 2 years of age. Analyses included logistic regression and classification tree modeling.
Results: Individuals who experienced many respiratory viral infections (11-20) during their first two years of life had a higher prevalence of allergies compared to their peers with fewer than 10 respiratory viral infections; 58% vs, 34% (p=0.005). Cytomegalovirus (CMV) seropositivity at two years of age was associated with allergy at age 20 (p=0.026). As expected, parental allergy was also linked to the development of allergy.
Conclusion: Individuals who experienced frequent respiratory viral infections during early childhood, were seropositive for CMV by age two, and had two allergic parents, consistently developed allergic disease by age 20. Preventive strategies targeting early viral respiratory infections may help reduce future allergy.