Researchers say they have pinpointed a major predictor of the development of childhood asthma: the common cold virus, or rhinovirus.

Infants who have viral respiratory illnesses with wheezing are known to have a higher risk of developing asthma sometime in childhood. Until recently, it was not known whether every type of respiratory virus that produces wheezing presents a similar risk of causing asthma.

In a study that used new techniques to identify different viruses, researchers now believe they have identified rhinovirus, or RV, as the main indicator of future asthma.

'The results of this study represent important advances in our understanding of childhood asthma.'—Dr. John E. Heffner, ATS past president

The study results are in the first October issue of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society (ATS).

"We have found that rhinovirus, the most common cause of colds, contributes a disproportionate amount towards future asthma development in comparison to other viruses that also cause childhood wheezing," said principal investigator Dr. Robert F. Lemanske Jr. of the University of Wisconsin School of Medicine and Public Health.

Researchers at the university studied more than 250 newborns at high risk for asthma, meaning one or both of each baby's parents had allergies or asthma.

The children were followed from birth to six years old, and tested for the presence of specific viruses during wheezing illnesses.

At age six, 28 per cent of the children had asthma and those who had wheezed with RV represented a large number.

The older the children were when they had wheezing with RV, the greater the effect.

Mild viral illnesses important too

Children who wheezed with RV during the first year of life were nearly three times as likely to have asthma at age six. Children who wheezed with RV in their second year of life were more than six times as likely to have asthma. Wheezing with RV at three years old increased asthma odds by more than 30 times.

"Indeed, nearly 90 per cent of the children wheezing with RV during year three subsequently developed asthma at age six," wrote the study's lead author, Dr. Daniel J. Jackson. "Wheezing RV illnesses occurring at any time during the first three years of life were associated with a nearly tenfold increase in asthma risk at six years."

Children who wheezed with respiratory syncytial virus (RSV), another common respiratory ailment, did not have an increased asthma risk.

Whether RV causes asthma to develop or just reveals children already predisposed to the disease is an open question.

"The results of this study represent important advances in our understanding of childhood asthma," said Dr. John E. Heffner, past president of the ATS. "Mild viral illnesses may be just as important for later asthma as more severe infections."