To the Editor.
—The article by Dr Fiscus and colleagues1 on perinatal zidovudine treatment in North Carolina provides encouraging data regarding effective strategies for prevention of perinatal human immunodeficiency virus (HIV) infection. Unfortunately, their geographic comparisons did not use standard definitions, leaving some question regarding the validity and interpretation of the urban and rural differences they report. Two geographic classification systems most often used in health-related research are those of the US Bureau of the Census (Census) and the US Office of Management and Budget (OMB).2,3 The Census characterizes all cities and places with 2500 or more people as "urban" and the remainder as "rural." In contrast, OMB classifies US counties as metro politan or nonmetropolitan, based on whether they are located within a metropolitan statistical area (MSA). Metropolitan statistical areas are counties, groups of counties, or, in New England, towns, representing economic areas with a central city
Cohn SE, Klein JD. Perinatal HIV Infection. JAMA. 1996;276(7):527-528. doi:10.1001/jama.1996.03540070023020