Ambient levels of air pollution during the winter months are not associated with asthma flare-ups in urban minority children with moderate-to-severe disease, according to a report in Journal of Allergy and Clinical Immunology for November.

“Most studies that have looked at the link between air pollution and asthma have involved mild asthmatics,” lead author Dr. Nathan Rabinovitch, from the National Jewish Medical and Research Center in Denver, told AMN Health. “We were interested in knowing what happens in a population with more severe disease.”

In earlier studies, the effects of air pollution on asthma outcomes were limited, Rabinovitch noted. “We hypothesized that perhaps we would see more effects in patients with moderate-to-severe asthma.”

To investigate, the researchers correlated pollution levels with asthma outcomes in children with moderate-to-severe asthma who were evaluated over three consecutive winters in Denver. The number of children evaluated in year one, two, and three were 41, 63, and 43, respectively.

The winter months were selected because this is the season when air pollution levels peak and because it is the season most often evaluated in past studies, Rabinovitch explained.

Despite using a study group with more severe disease, air pollution levels seemed to have no effect on asthma flare-ups or lung function. Moreover, there was only a weak link between carbon monoxide levels and bronchodilator use as well as between ozone levels and daytime symptoms.

As to the reason for this lack of association, Rabinovitch suggested “it could relate to a threshold effect. Perhaps, because it was the winter the children were staying indoors and were not exposed to enough pollution to have an effect.” However, no one has shown this threshold to exist yet, he added.

“Another possibility is that there are some meteorologic [factors] that are really driving the association between air pollution and asthma,” Rabinovitch said.

Regardless of the reason, “it doesn’t look like air pollution has a big effect on asthma outcomes in children with moderate-to-severe disease - at least in Denver,” he concluded.

SOURCE: Journal of Allergy and Clinical Immunology, November 2004.