Purpose of the Study. As one dimension of the hygiene hypothesis, early infections may protect against the development of atopic disease. However, there are few long-term follow-up studies of the influence of early respiratory infections. This study investigates associations between early respiratory infections and diagnosed asthma, allergic rhinitis, and skin-prick sensitization in children at 10 years of age.
Study Population. A total of 2540 Norwegian children were followed prospectively from birth to the age of 10 years in the Oslo Birth Cohort.
Methods. Information on child’s health and environmental exposures, including experiences with respiratory infections, was recorded at birth and at 6 and 12 months. Current symptoms and “ever” doctor-diagnosed asthma and allergic rhinitis were compared with these early life exposures. A subset of the cohort underwent skin-prick testing.
Results. “Ever” diagnosis of asthma was positively associated with measures of early life infection. Current asthma was related to lower respiratory tract infection (adjusted odds ratio [aOR]: 2.1; 95% confidence interval [CI]: 1.3–3.0) and croup (aOR: 2.3; 95% CI: 1.3–4.2) in the first year. ORs for allergic rhinitis and skin-prick sensitization were smaller but “mainly positive.” Birth order and child care attendance at 1 year of age were not significantly associated with any of the studied outcomes.
Conclusions. Early respiratory infections did not protect against the development of atopic disease during the first 10 years of life. Rather, infections increased the risk for asthma at age 10.
Reviewer Comments. The hygiene hypothesis has been used to explain an inverse relation between early-life infection and allergic disease. Although a number of studies have described the relationship of early childhood infections and atopic disease, few have done so prospectively. This study, with its ORs near 1 with narrow CIs, shows a positive relationship of infections to atopy. Thus, it does not support the view of protection with increasing infection, bringing to light that this relationship is not as simple or direct as was first described. Additional prospective studies with long-term follow-up are required to further define this relationship. In addition, these results support previous conclusions that early childhood infection may be associated with an increased risk for future development of asthma. There continues to be many unanswered questions regarding the risks in susceptible hosts.
- Copyright © 2006 by the American Academy of Pediatrics