Nov. 21, 2008 -- When it comes to babies and asthma, timing is everything.
A new study shows that babies born four months before the peak of winter virus season are more likely to develop childhood asthma than babies born at any other time of year; that's because the timing increases the chance of a viral respiratory infection during infancy, which in turn increases the risk of childhood asthma. The date that winter virus season peaks can vary from year to year.
The study is published in American Journal of Respiratory and Critical Care Medicine.
Asthma is an increasingly important health concern. The prevalence of asthma increased 100% worldwide between 1985 and 2001, according to background information in the study. About 300 million people have asthma. Deaths from asthma are expected to increase 20% during the next decade.
Researchers looked at medical records of 95,310 children born between 1995 and 2000 and followed their health status until 2005. The children were all born in Tennessee and enrolled in the state's Medicaid program, called TennCare.
Scientists have known for some time that there is a link between infant viral respiratory infections and childhood asthma. However, they did not know whether viral respiratory infections cause asthma or whether the infections are simply a sign that a child is genetically predisposed to develop asthma. This study offers evidence that the former is true.
The researchers found that babies born four months prior to the peak of winter virus season had a 29% increased risk of developing childhood asthma compared to babies born one year before the winter virus peak.
Even armed with the new findings, preventing the infant respiratory infections that lead to childhood asthma is no easy task. It is hard to shield babies from such infections. About 70% of babies develop RSV (respiratory syncytial virus) during the first year of life.
However, the researchers argue that there may be a need for prevention strategies, such as vaccines, for babies at high risk for asthma.
"Prospective trials with antiviral strategies, including potential new vaccines targeting [respiratory viruses] in selected populations at risk should give us better understanding of the role of viral infections in early life in the causation of childhood asthma," writes Renato T. Stein, MD, PhD, of the PontifÃcia Universidade Catolica in Porto Alegre, Brazil, in an editorial published with the study.