Children who receive antibiotics before their first birthday are significantly more likely to develop asthma by age seven, finds a Canadian study.
The risk for asthma doubled in children receiving antibiotics for non-respiratory infections, as well as in children who received multiple antibiotic courses and who did not live with a dog during their first year, according to the study published in CHEST, the journal of the American College of Chest Physicians.
"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," lead study author Anita Kozyrskyj of the University of Manitoba in Winnipeg said in a news release.
"Our study reported on antibiotic use in children being treated for non-respiratory tract infections, which distinguishes the effect of the antibiotic."
Kozyrskyj and colleagues from the University of Manitoba and Montreal's McGill University used a prescription database to monitor the antibiotic use of 13,116 children from birth to age seven, noting antibiotic use during the first year of life and presence of asthma at age seven.
The study found that six per cent of children had asthma at age seven, while 65 per cent had received at least one antibiotic prescription during the first year of life -- 40 per cent for middle-ear infections, 28 per cent for other upper respiratory tract infections such as sinus infections, 19 per cent for lower respiratory tract infections such as bronchitis and pneumonia, and seven per cent for non-respiratory tract infections.
When the researchers looked at reasons for antibiotic use, asthma at age seven was almost twice as likely in children receiving an antibiotic for non-respiratory tract infections compared with children who had not received the drugs.
The likelihood of asthma rose with the number of antibiotic prescriptions: children given more than four courses of the drugs had 1.5 times the risk of asthma compared with children who received no antibiotics during infancy.
The study also found that children who received multiple rounds of antibiotics and who were born to mothers without a history of asthma were twice as likely to develop asthma than those not receiving antibiotics.
Furthermore, 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 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."
