The new research from Vanderbilt University has found that while having clinically significant bronchiolitis at any age during infancy was associated with an increased risk of childhood asthma, for autumn babies, that risk was the greatest.
"Infant age at the winter virus peak following birth independently predicts asthma development, with the highest risk being for infants born approximately four months prior to the peak, which is represented by birth in the fall months in the Northern hemisphere," said Tina V. Hartert, M.D., M.P.H., associate professor of medicine and director of the center for Asthma Research at Vanderbilt University, and principal investigator of the study.
"Birth during this time conferred a nearly 30 percent increase in odds of developing asthma," she added.
The study analysed the birth and medical records of more than 95,000 children and their mothers in Tennessee to determine whether date of birth in relationship to the peak in winter respiratory viruses posed a higher risk for developing early childhood asthma.
The researchers suggest two non-mutually exclusive possible reasons for the link, one, that there is a genetic susceptibility common to both bronchiolitis and the development of asthma and the other that an environmental exposure such as winter viral infection causes asthma.
"The risk of progressing from bronchiolitis to asthma is almost certainly influenced by genetic factors," wrote Dr. Hartert.
"However, if this association were due only to genetic factors, there would be a seasonal effect on infection but not on asthma...Instead we have shown that there is variation in the risk of developing asthma by the timing of birth in relationship to the winter virus peak for each year studied.
"This supports a causal relationship of childhood asthma with the winter virus peak after birth," she added.
The research was published in the first issue for December of the American Journal of Respiratory and Critical Care Medicine, a publication of the American Thoracic Society.