NEW YORK (Reuters) - Cockroaches have been identified as a possible explanation for dramatic neighborhood variations in asthma rates among New York City children. In some neighborhoods, 19 percent - nearly 1 in 5 - of children have asthma, while in others the rate can be as low as 3 percent. Heavy traffic, industrial incinerators, and other outdoor air pollution sources have all been blamed in the past. But researchers at Columbia University have now found that children living in neighborhoods with high rates of asthma were twice as likely to carry antibodies against a cockroach protein in their blood, a sign the children had been exposed to the insects and were likely allergic to them. In addition, homes in the neighborhoods with high rates of asthma contained more of the allergen produced by cockroaches in household dust. The study provides further evidence that cockroach exposure is part of the story, said study author Matthew Perzanowski. Cockroach allergen really could be contributing to disparities in asthma prevalence, even in an urban environment like New York City. For the study, published in the Journal of Allergy and Clinical Immunology, Perzanowski and his team visited in the homes of 239 seven- and eight-year-olds, half of whom lived in areas with high asthma rates.