For more than 50 years, researchers have described childhood asthma as a plague of the inner city -- urban areas where 20 percent or more of the population lives below the poverty line. But a new study by researchers from Johns Hopkins University School of Medicine suggests that isn't true, and that race, ethnicity and poverty are more closely associated with the lung disease than location in urban neighborhoods.

When they looked at data for 23,065 children across the United States collected in the National Health Interview Survey, the researchers found that self-reported asthma attacks were distributed about equally between inner city areas and all others. More importantly, they found that "black race, Puerto Rican ethnicity and poverty rather than residence in an urban area per se are the major risk factors for prevalent asthma. These findings suggest that the concept of inner-city asthma might need to be refined."

"What we found is there is a lot of variation," Corinne Keet, an assistant professor of pediatrics, said in an interview. Asthma rates were high in northeastern inner cities but also high in poor suburban midwestern areas, she said. Most of the variation can be explained by race, ethnicity and poverty, rather than by location, she said.

Overall, 12.9 percent of children who live in inner cities have asthma, compared to 10.6 percent of children who live elsewhere, according to the analysis published Monday Tuesday in the Journal of Allergy and Clinical Immunology. The difference disappeared when variables such as race, ethnicity and geography were factored in.

For African-Americans and Puerto Ricans, higher risk of asthma may be genetic, Keet said. For the poor, it may be stresses such as exposure to mouse and cockroach allergens, cigarette smoke, a higher rate of pre-term births and more maternal stress, she said.

Keet said it's unclear whether inner-city children who have asthma may suffer more severe symptoms as a result of allergens there. Another study is being conducted to determine that, she said.

With asthma rates rising and more of the poor in the suburbs, Keet said, it's important that public health officials know the true prevalence of the disease, she said. "In this survey we estimate that inner-city areas now house only 8% of all children with current asthma compared with the 46% living in suburban or wealthier urban areas, which follows a similar distribution to children as a whole," Keet's team wrote.