Early Exposure To Germs May Promote Future Immunity

New York Times Syndicate

Raja Mishra

Parents have long shuddered at the thought of their little ones inhaling the germ-ridden air of day care centers, where every sniffle, cough or sneeze seems pregnant with disease.

But it may actually be healthy in the long run.

Researchers in Arizona found that children who were exposed to day care centers at an early age were less likely to develop asthma when they were older. Their theory is that exposure to viruses and bacteria when very young girds the immune system against asthma developing later.

``The decision to put one's child in day care depends on many factors. But parents from families with histories of asthma might want to go ahead and expose their child to more children early in life,'' said Dr. Thomas Ball, assistant professor of clinical pediatrics at the University of Arizona, and co-author of the study of published in the current New England Journal of Medicine. ``Infants who were exposed to more children in or outside of the house were almost half as likely to develop asthma later in childhood.''

The counter-intuitive finding may be a clue in a long-running medical mystery: what causes asthma and why have asthma cases skyrocketed in the last 20 years?

Scientists are almost certain there is a genetic component but the environmental triggers remain murky. Pollution was once thought the culprit but lost luster after a series of studies in the 1990s found lower asthma rates among residents of heavily-polluted East German cities than in their cleaner West German counterparts.

The Arizona study appears to lend weight to the contender now in vogue, the so-called Hygiene Hypothesis, which says: modern improvements in hygiene that limit exposure to disease early in life produces weaker, more asthma-vulnerable, immune systems later in childhood.

``(The Arizona study) does seem to support that hypothesis,'' said Dr. Hans Oettgen, clinical director of immunology at Children's Hospital. ``But it's still at the state where it is a hypothesis. It hasn't been nailed down with 100 percent certainty.''

Asthma is considered a major public health nuisance, affecting the lives of almost 15 million Americans, nearly a third of them children, with its recurring bouts of breathlessness and wheezing. Severe asthma attacks can be fatal. The condition occurs when the lungs are clogged with sticky mucus that restricts airflow.

Sufferers must often carry around bronchodilators or take anti-inflammatory drugs. Childhood asthma grows milder with age but could permanently reduce lung capacity by 10 percent.

Oettgen cautioned that the Arizona study does not mean hesitant parents should rush their children to the nearest day care center.

``You really have to hesitate when talking about exposing your kids to anything,'' he said. ``A lot of infections still have bad outcomes.''

However, in an editorial accompanying the study, whimsically titled ``Please, Sneeze on my Child,'' Dr. Sandra Christiansen of the Scripps Research Institute in California wrote: ``For those of us who share the furtive guilt of having left marginally ill toddlers at day care, these findings also offer a sense of relief.''

The Arizona researchers were even more confident about their findings.

``Infections early in life help steer infants developing immune response towards a non-allergic road,'' said Ball.

But Ball and his colleagues stressed their study is only a small piece in the quest to understand and prevent asthma. The condition has exploded around the world in the last two decades but not uniformly. It's prevalence increased by 30 percent in Australia and Britain but only 2 percent in China.

Asthma tends to run in families but that doesn't guarantee an asthma sufferer's child will have it. Some environmental risk factors have been identified: smoking by parents, indoor exposure to allergens, absence of breast-feeding and a diet high in a certain type of fat.

In 1988, an English researcher found that children from large families, where illness is more common, were less likely to have hay fever. This launched the Hygeiene Hypothesis. Soon studies were produced that showed kids exposed to pets early in life were less likely to have allergies, as was the case with kids who grow up on farms - both environments alive with allergens and potential lung irritants.

``But we still don't know the cause,'' said Ball.

-----

(The Boston Globe web site is at http://www.boston.com/globe)