"Asthma Alley": a space clustering study of asthma in Brooklyn, New York City.

A certain section of the borough of Brooklyn has sometimes been referred to as "Asthma Alley," expressing a feeling that this area in Brooklyn shows a markedly higher rate of asthma than adjacent areas. This study describes an epidemiologic method developed to determine whether the popular perception of spatial clustering of cases reflects reality. The spatial distribution of respiratory visits to the emergency room is taken as a reference against which clustering of asthma visits is compared, on the assumption that it is a good measure of the proportion of people in that area that make use of the emergency room facilities. From approximately 9,000 visits for asthma during the study period we were able to show that: (1) the differences in distribution of asthma cases among the health areas of Brooklyn are statistically significant; and (2) the health areas that show an excess of asthma visits lie along a belt east of the two hospitals and coincide with the popular impression of the location of "Asthma Alley."