Kids’ Exposure to Germs May Be a Good Thing

Infants who go to day-care centers or who have older siblings are less likely than those who don’t to develop asthma later in childhood, perhaps because they’re exposed to more germs, researchers reported Wednesday.

The findings provide strong support for the provocative but increasingly accepted theory that exposure to microbes early in life may help the immune system mature properly, lowering the risk of asthma and allergies.

Small families, good sanitation and widespread antibiotic use--all of which reduce childhood exposure to bacteria and viruses--may be part of the reason for the dramatic increase in asthma and allergies seen in the United States and other industrialized countries over the last three decades.

“I think it’s a fascinating area. It’s probably not just specific to asthma,” said Robert A. Wood, an associate professor of pediatrics at Johns Hopkins University School of Medicine. In the future, he added, if additional research clarifies the link between early exposures and fine-tuning of the immune system, “it’s extremely promising that you’d be able to expose a newborn to the right mix of safe bacteria and potentially turn the allergy system way down or completely off.”

In the new study, babies who entered day care before the age of six months had only 40% the risk of asthma seen in those who weren’t exposed to day care or older siblings.

An estimated 17.3 million Americans suffer from asthma, a chronic and often progressive disorder in which small air passages in the lungs become temporarily blocked, causing difficulty breathing. The figure has more than doubled since 1980, when there were 6.7 million asthmatics. Asthma, which often develops during childhood, is one of the most common chronic illnesses in the United States, causing almost 500,000 hospitalizations and more than 5,000 deaths annually and costing an estimated $14.5 billion per year.

Asthma experts, who have been puzzled by the sharp rise in the disease’s frequency, said the large, long-running study by Arizona researchers helps explain previous, seemingly discrepant findings about the effects of day care on the disorder. The new study found that infants who were exposed to other children had more wheezing episodes during their preschool years, chiefly because they suffered more colds and other infections. But they were less likely to develop asthma, perhaps because early experience with bacteria and viruses favorably influenced their immune systems.

Researchers at the University of Arizona’s Respiratory Sciences Center studied 1,035 children from birth to age 13, collecting detailed information on them and their illnesses.