Children treated with antibiotics before they turn one appear significantly more likely to develop asthma by age seven, Canadian researchers say.

A team from the University of Manitoba and McGill University in Montreal looked at the medical records of more than 13,000 children up to seven years old.

"Antibiotics are prescribed mostly for respiratory tract infections, yet respiratory symptoms can be a sign of future asthma. This may make it difficult to attribute antibiotic use to asthma development," said lead author Anita Kozyrskyj of the University of Manitoba.

"Our study reported on antibiotic use in children being treated for nonrespiratory tract infections, which distinguishes the effect of the antibiotic," she added in a release.

In the June issue of the journal Chest, the researchers found that six per cent of children had asthma at age seven.

The risk for asthma  was nearly doubled, 1.86 times higher, among children who took antibiotics for non-respiratory tract infections, compared with children who never took the drugs, the researchers found.

The increased risk was still present among children generally considered to be at a lower risk of asthma, including those in rural areas, Dr. Karen Binkley, an associate professor at the University of Toronto and an allergist at St. Michael's Hospital, told CBC Newsworld on Tuesday.

"Antibiotic use in early life was associated with the development of childhood asthma, a risk which may be reduced by avoiding use of broad spectrum cephalosporins," the study's authors wrote.

Reasons for antibiotic use during the first year of life included:

• Otititis media or middle-ear infection — 40 per cent.
• Other upper respiratory tract infections such as bronchitis or pneumonia — 28 per cent.
• Lower respiratory tract infections — 19 per cent.
• Non-respiratory tract infections such as urinary infections — 7 per cent.

Watching children with ear infections for 24 to 48 hours, rather than immediately prescribing drugs, is one alternative to using antibiotics, Binkley suggested.  

"Understanding the relationship between antibiotic use and asthma can help clinicians make more informed decisions about treatment options for children," said Dr. Mark Rosen, president of the American College of Chest Physicians, which publishes the journal.

Fido favoured

Asthma risk also appeared to be higher among children who did not have a family dog during their first year of life.

"Dogs bring germs into the home, and it is thought that this exposure is required for the infant's immune system to develop normally," Kozyrskyj said. "Exposure to germs is lower in the absence of a dog. The administration of an antibiotic may further reduce this exposure and increase the likelihood of asthma development."

A 10-year study published in 2002 also suggested that infants who live in homes with two or more cats or dogs appeared to be lower risk for developing allergic reactions that may lead to asthma.

The researchers also accounted for asthma risk factors such as gender, urban or rural location, neighbourhood income and number of siblings.

Previous research has also suggested early antibiotic use may be linked to an increased risk of asthma, but some studies relied on parents recalling what antibiotics their children were given after the youngsters had grown up.