FRIDAY, Nov. 21, 2008 (HealthDay News) -- The season of a baby's birth may help predict that child's risk of asthma, new research suggests.
Babies born in autumn -- about four months before the peak of winter virus season -- have almost a 30 percent increased risk of asthma compared to babies born at other times of the year, reports a study in the first December issue of the American Journal of Respiratory and Critical Care Medicine.
"Children in the Northern hemisphere born in the fall months have the highest rates of asthma, which suggests that winter viruses, like RSV, cause asthma," said study senior author Dr. Tina Hartert, director of the Center for Asthma Research and Environmental Health at Vanderbilt University School of Medicine, in Nashville, Tenn.
"What we need to prove now is that preventing these viruses could prevent asthma," she added.
Respiratory syncytial virus (RSV) is a very common infection. In fact, Hartert said that about 70 percent of U.S. infants will have an RSV infection before their first birthday. Not all children who have an RSV infection will develop asthma, but those with more severe infections appear to have a higher risk. More than 40 percent of infants hospitalized for a respiratory virus develop asthma by their teen years, according to background information in the study.
The author of an accompanying editorial in the same issue of the journal said genetic factors play a role as well. "Asthma, like many other complex diseases, has a genetic background that is importantly affected by the surrounding environment. Different factors, like allergies or maternal/paternal history of asthma, when in combination with early life infections by respiratory viruses, seem to increase substantially the risk for asthma, or at least, persistent wheeze," said Dr. Renato Stein, head of the pediatric pulmonary service at Pontificia Catholic University in Porto Alegre, Brazil.
What hasn't been clear in the past is whether RSV and other viruses actually cause asthma, or whether children who are predisposed to asthma are the ones most likely to get such viruses, according to Dr. Jennifer Appleyard, chief of allergy and immunology at St. John Hospital in Detroit.
The current study, which included a group of more than 95,000 infants born between 1995 and 2000, hoped to answer that question.
All of the infants were part of the Tennessee Medicaid program and were followed from birth through early childhood to see if the timing of birth in relation to winter virus season had any effect on the development of asthma.
And, the researchers found that it clearly did. Babies born in the fall, which is generally about four months before the peak of the winter virus season, had a 29 percent higher risk of asthma, according to the study.
For fall-born babies, said Hartert, the winter virus season tends to coincide with a vulnerable period of development, where babies are transitioning from maternal antibodies to their own. But, she said, babies' immune systems aren't really developed until about 6 months of age.
Hartert said she "hopes this study's findings will generate heightened interest in development of an RSV vaccine." She said that RSV is unique among viruses because the human body doesn't ever develop antibodies against it. She said there are vaccines in development currently, but that they're "probably a ways off."
Appleyard said that parents shouldn't worry if they've had, or are going to have a fall baby, "because no one specific trigger is going to be the cause of all asthma."
Likewise, she said, don't feel like you're to blame if your child has ever had RSV, because most children have had this ubiquitous virus.
However, Hartert, Appleyard and Stein all suggested that parents might want to take steps to try to reduce the risk of infection. If it's at all possible, said Stein, try to avoid day care before the age of 3. Hartert said that parents should also employ good hygiene and infection-control measures, such as staying away from sick children and washing their hands frequently.
To learn more about children and asthma, visit the American Academy of Family Physicians.