Antibiotic use in infants may increase asthma risk.

Giving antibiotics for a non-respiratory tract infection to an infant younger than 1 greatly increases the odds that the child will develop asthma, according to new research reported by "HealthDay News" June 11.

The study found that the risk was highest for those infants who received multiple courses of antibiotics and those who received prescriptions for broad-spectrum antibiotics.

"Asthma is a multi-factorial disease, and we've found evidence of an association with first-year-of-life antibiotic use and asthma," said the study's lead author, Anita Kozyrskyj, Ph.D., an associate professor at the University of Manitoba in Winnipeg, Canada.

One hypothesis, Kozyrskyj added, is that broad-spectrum antibiotics are killing off too many good bacteria.

"It may be that you need the presence of good bacteria during the first year of life for the immune system to develop normally, and the antibiotics are killing off some of the natural microflora in the gut," she said.

The study findings are published in the June issue of the journal "Chest."

Kozyrskyj and her colleagues followed almost 14,000 children from birth in 1995 until 2003, when all of the children had reached 7 years of age. Data came from the Manitoba Health Services Insurance Program and included information on physician visits, prescriptions, hospitalizations and health diagnoses.

Additionally, the researchers linked this data to data on the mothers of these children to see if there was a maternal history of asthma. Parents also completed surveys on home and environmental exposures.

Two-thirds of the youngsters had received at least one antibiotic prescription during their first year of life, many of them for broad-spectrum antibiotics, according to the study. The more antibiotics received, the greater the risk of asthma, the study revealed.

Children who received one to two courses of antibiotics had a 21% increased risk of asthma; those given three to four courses of antibiotics had a 30% rise in risk; while youngsters given more than four courses of antibiotics had a 46% increased risk of asthma, Health-Day reported.

Children given antibiotics for non-respiratory tract infections, such as urinary-tract infections, were as much as 86% more likely to develop asthma than those treated for respiratory infections.

Other factors that increased the risk of asthma included a family history, living in an urban area and being male. Having a sibling conferred a slight protective effect, as did having a dog for children who received multiple courses of antibiotics. In children who had more than four courses of antibiotics before age 1, having a dog decreased the risk of asthma by 28%.

Alan Khadavi, M.D., a pediatric asthma specialist at New York University Medical Center, told Health-Day, "If your child under 1 year is sick, have him or her evaluated. Don't push for antibiotics. But on the other hand, if it's a serious infection that needs to be treated, I wouldn't worry too much about the asthma risk. If it's a mild infection, a watch-and-wait approach won't be harmful if they're under a physician's care."

Kozyrskyj recommended that physicians start by prescribing narrow-spectrum antibiotics, such as amoxicillin, for their youngest patients, and then if necessary, try a broad-spectrum medication.