Antibiotics in infancy tied to asthma.

Children given multiple doses of antibiotics before their first birthdays have a heightened risk of asthma later, a study shows.

Researchers analyzed the medical records of 13,116 children born in Manitoba in 1995. Roughly 6 percent of the group developed asthma by age 7.

Kids getting more than four courses of antibiotics during the first year of life were 1.5 times as likely to develop asthma by age 7 as kids getting no such drugs, the researchers report in the June Chest.

In a further analysis, the scientists took into account the reasons for the prescriptions. "Respiratory-tract infections might be an early indication of asthma, sometimes associated with colds and wheezing," says study coauthor Anita L. Kozyrskyj, an epidemiologist at the University of Manitoba in Winnipeg. To isolate the effect of antibiotics, she and her team separately analyzed the smaller group of children that received the drugs for reasons other than respiratory and ear infections.

These infants received antibiotics mainly for skin and urinary-tract infections. But even among such infants who got only one or more courses of antibiotics, the asthma risk was nearly doubled by age 7 compared with that in kids not getting any drugs.

Because asthma is a chronic overreaction of the immune system, Kozyrskyj offers two possible explanations for the findings.

First, early exposure to toxins made by microbes might help an infant's immune system develop normally (SN: 8/26/00, p. 134; 8/14/99, p. 108), and antibiotics administered during the first year of life would reduce that exposure. Another possibility is that a child's intestines need to c harbor friendly bacteria, or microflora, for that child to develop a sound immune system. "Taking antibiotics may suppress these good bacteria," Kozyrskyj says. --N.S.