Antibiotics in infancy may double asthma risk
British Columbia Research
Sharon Kirkey
CanWest News Service
Tuesday, March 14, 2006
Babies treated with an antibiotic before their first birthdays are twice as likely as antibiotic-free infants to develop asthma, new Canadian research suggests. And the risk of the chronic lung disease grows each time a baby is prescribed one of the drugs.
“This is the best evidence we have right now, and the best evidence that we have looks like there is potentially an association” between antibiotic exposure early in life and asthma, said lead author Dr. Carlo Marra, an assistant professor in pharmaceutical sciences at the University of British Columbia in Vancouver. “People should not be prescribing antibiotics unless they’re really necessary.” The researchers, who pooled data from eight studies that included more than 12,000 children, found that children were up to 2.9 times more likely to develop asthma if they had been given an antibiotic before the age of one, compared with children who had not received an antibiotic.
In a second analysis, this one involving more than 27,000 children, the B.C. team found a 16% increase in risk for each additional course of antibiotics given to children. “A lot of the infections in children — things like otitis media (middle ear infections), bronchitis and upper respiratory tract infections — are being over-treated,” Dr. Marra said. “Those are the biggest indications for antibiotic utilization, and, particularly for bronchitis and upper respiratory tract infections, a lot of those are viral.” Antibiotics kill bacteria, not viruses.
The findings are published in this month’s issue of the journal CHEST.
Asthma, which causes wheezing, coughing and chest tightness, is now the most common chronic disease of childhood. Between 10 and 20% of children in Canada have it, and about 20 children and 500 adults die each year from asthma, according to the Lung Association.
A study released in January found the percentage of boys in Canada aged eight to 11 who were diagnosed with asthma increased from 16% in 1994/95 to 20% in 1998/99. For girls of the same age, asthma jumped from 11% to about 15%.
Asthma rates have climbed dramatically in the last quarter century, and researchers have been trying to understand why. The disease’s rise has been linked to everything from ground-level ozone to chlorinated pools. But one theory blames exposure to antibiotics and the “hygiene hypothesis” — the idea that kids who are not exposed to enough microbes and germs develop weakened immune systems.
Two types of white blood cells, T-helper 1 cells that fight bacteria and viruses, and T-helper 2 cells that respond to parasites, normally live in harmony. But children not exposed to enough viruses and bacteria may develop jittery immune systems, with an “underdeveloped Th1 system, and an over-developed Th2 system,” Dr. Marra said. As a result, children overreact to pollen, dust mites and other normally harmless substances. Other researchers have probed the asthma-antibiotic connection, but with conflicting results.
The Canadian researchers decided to combine the data to look at whether the use of antibiotics or dose matters.
Dr. Marra’s team reviewed studies that compared exposure to at least one antibiotic to no exposure in the first year of life. Of the 12,082 children included, 1,817 cases of childhood asthma were reported. Overall, infants given at least one antibiotic were 40% to roughly three times more likely to develop asthma as childhood progressed.
However, the association was highest in studies where parents of asthmatic children were asked, did your child ever receive an antibiotic in the first year of life? They may be more likely to report antibiotic use than other parents, because it’s human nature for people with a disease to want to explain it. It’s also possible that babies who have early asthmatic symptoms are being misdiagnosed with a respiratory tract infection and put on antibiotics, because asthma is difficult to diagnose in children under one. In other words, the asthma came before the antibiotic.
Bigger and better-designed studies are needed, Dr. Marra said. The researchers are embarking on a study funded by the B.C. Lung Association that will involve about 200,000 children across the province to determine “if there really is an association between antibiotic association and asthma” and whether there are different risks with different types of antibiotics.
