Fewer early infections don't mean more allergies

NEW YORK (Reuters Health) - The idea that an increase in allergies and asthma is a result of a reduction in childhood infections seems not to hold up, researchers report.

Preventing common respiratory infections and stomach infections in child daycare centers had no impact on the later development of asthma, nasal allergies or eczema, according to a follow-up survey conducted 12 years later.

The findings do not support the “hygiene hypothesis,” which theorizes that reduced exposure to infections in childhood leads to greater allergic sensitization, conclude Dr. Teija Dunder and colleagues from the University of Oulu, Finland.

The magnitude of the reduction in early infections “should have led to an increase in asthma rates if the hygiene hypothesis were to apply to common childhood infections,” Dunder and colleagues point out in the Archives of Pediatrics and Adolescent Medicine for October.

Between 1991 and 1992, a total of 1376 children attended daycare centers that were either part of a hygiene intervention effort or not. The intervention included several steps, the most important of which was improvement of hand hygiene using an alcohol-based hand rub, the authors note

Children attending hygiene intervention centers had 15 percent fewer days with symptoms of infections and 24 percent fewer prescriptions for antibiotics than those attending “control” daycare centers.

A follow-up survey of 928 adolescents who attended the daycare centers as young children showed no differences between the two groups in the development or severity of asthma, allergic rhinitis or eczema.

Asthma was diagnosed in 48 of 481 adolescents from intervention daycare centers (10 percent) and in 46 of 447 controls (10 percent). Similarly, no difference was found in the number of children who had a diagnosis of other allergic diseases or who had reported such symptoms.

The researchers conclude that this shows that a reduction in infections in children attending daycare centers can be achieved by simple infection prevention practices. “We can now say that it proved to be safe because it had no effect on later (allergic illness).”

SOURCE: Archives of Pediatrics and Adolescent Medicine, October 2007.