Air pollution tied to babies' ear infection risk

NEW YORK (Reuters Health) - Babies and toddlers who live in areas with moderate air pollution may have a higher risk of middle-ear infection than those breathing cleaner air, a Canadian study suggests.

Smoke flows from the Fertiberia fertilizer factory in an industrial zone of Huelva, southern Spain, June 4, 2008. REUTERS/Javier Barbancho

The findings, reported in the journal Epidemiology, do not prove that air pollution itself was the cause. But if it is, that would allow parents to influence their kids’ risk of infection by moving to a place with better air.

Middle-ear infections, also called otitis media, are common among young children, with those younger than 2 being most susceptible. They are caused by a viral or bacterial infection, and usually arise after a child has had a cold, sore throat or other upper-respiratory tract illness.

Earlier studies have suggested that air quality can play a role in young children’s vulnerability to middle-ear infections; exposure to second-hand smoke, for instance, has been linked to an increased risk. But little research has looked at the relationship between outdoor air quality and ear aches.

For the new study, researchers tracked doctor visits for middle-ear infections among more than 45,000 Canadian children followed from birth until age 2. All of the children lived in an area of British Columbia with relatively good air quality.

The investigators used data from government air-quality monitors to estimate each child’s exposure to air pollutants, based on the family’s home address. They then looked at the relationship between the children’s ear infections and their air-pollution exposure in the two months prior to the infection.

Overall, 42 percent of the children visited the doctor for a middle-ear infection at least once in the first two years of life. When the researchers looked at air pollution levels, they found a correlation between ear infections and exposure to certain pollutants -- even with factors such as the time of year (ear infections are most common in fall and winter), neighborhood income levels and whether mothers smoked during pregnancy.

For example, when dividing children into four groups of exposure to nitric oxide, a traffic-related pollutant, those with the highest exposure were 10 percent more likely to have a doctor visit for middle-ear infection than those in the lowest.

Two other pollutants were also linked to moderately increased risks: particulate matter -- the fine particles emitted via car exhaust, as well as power plants and other industrial sources -- and smoke from wood burning.

Children breathing the highest levels of wood smoke were 32 percent more likely to have doctor visits for middle-ear infections than those breathing the least.

No other individual pollutants were tied to children’s risk of infection.

The findings do not prove that air pollution directly contributes to middle-ear infections, according to lead researcher Dr. Elaina A. MacIntyre, of the German Research Center for Environmental Health in Neuherberg and the University of British Columbia in Vancouver.

There could be other factors, unmeasured in this study, that account for the link, she noted in an email to Reuters Health.

Among the questions for future studies, MacIntyre said, is whether there are biological mechanisms by which air pollution could raise a child’s susceptibility to middle-ear infections.

Air pollution is known to help trigger airway inflammation, so that is one way it might it be involved.

The risks linked to air pollutants in this study were small, MacIntyre noted, but air quality is a factor that can be changed. If future studies confirm air pollution as a risk factor for ear infections, then efforts to improve air quality could have the added benefit of curbing a common and costly childhood ill, she and her colleagues say.

In the U.S. alone, middle-ear infections account for an estimated 25 million doctor visits each year, with treatment costs of $3 billion, according to the American Academy of Otolaryngology-Head and Neck Surgery.

In general, experts recommend that parents help lower their children’s risk of the infection through regular hand-washing to cut the odds of catching a cold or the flu; keeping infants upright during bottle-feeding; and having them receive the recommended vaccines against the flu and pneumococcal infection, either of which can lead to a middle-ear infection.

SOURCE: Epidemiology, online October 27, 2010.