A new study has found that kids who receive antibiotics before they even celebrate their first birthday are at an increased risk of developing asthma by the time they turn seven.

The study was carried out by a team from the University of Manitoba and McGill University in Montreal, led by Dr Anita Kozyrskyj, University of Manitoba, Winnipeg, Canada [Images]. They used a prescription database that enabled them to monitor the antibiotic use of 13,116 children from birth to age 7, specifically noting antibiotic use during the first year of life and the presence of asthma at age 7.

The reason for antibiotic use was categorised by lower respiratory tract infection (bronchitis, pneumonia), upper respiratory tract infection (otitis media, sinusitis) and non-respiratory tract infection (urinary infections, impetigo).

Risk and protective factors also were noted, including gender, urban or rural location, neighbourhood income, number of siblings at age 7, maternal history of asthma and pets reported living in the home.

Within the study group, six percent of children had current asthma at age 7, while 65 percent of children had received at least one antibiotic prescription during the first year of life.

Of the prescriptions, 40 percent of children received antibiotics for otitis media, 28 percent for other upper respiratory tract infections, 19 percent for lower respiratory tract infections, and seven percent for non-respiratory tract infections.

Results showed that antibiotic use in the first year was significantly associated with greater odds of asthma at age 7. This likelihood increased with the number of antibiotic courses, with children receiving more than four courses of antibiotics having 1.5 times the risk of asthma compared with children not receiving antibiotics.

When researchers compared the reason for antibiotic use, their analysis indicated that asthma at age 7 was almost twice as likely in children receiving an antibiotic for non-respiratory tract infections compared with children who did not receive antibiotics.

"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. Our study reported on antibiotic use in children being treated for non-respiratory tract infections, which distinguishes the effect of the antibiotic," said Dr Anita Kozyrskyj.

They also found that kids who received multiple antibiotic courses and who were born to women without a history of asthma were twice as likely to develop asthma than those not receiving antibiotics. Furthermore, the absence of a dog during the birth-year doubled asthma risk among children taking multiple courses of antibiotics.

"Dogs bring germs into the home, and it is thought that this exposure is required for the infant's immune system to develop normally. Other research has shown that the presence of a dog in early life protects against the development of asthma," said Dr Kozyrskyj.

 "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," she added.