To the Editor.
—Human immunodeficiency virus (HIV) prevalence among injection drug users (IDUs) is thought to be low in cities in the western United States when compared with New York, NY, Miami, Fla, and Chicago, Ill. Data from published serological surveys of IDUs in San Francisco, Calif, suggest seroprevalence of 8% among IDUs enrolled in drug treatment programs during 1988 through 19901 and a mean seroprevalence of 12% (range, 10% to 14%) among heterosexual, street-recruited IDUs during 1987 through 1992.2 These studies also suggest declining incidence of HIV among San Francisco IDUs in the late 1980s. However, this epidemiologic portrait of center-city populations may not accurately portray conditions in neighboring communities.The Urban Health Study conducts studies of street-recruited IDUs in Northern California. We found higher HIV seroprevalence rates at baseline in smaller, predominantly African-American neighborhoods outside San Francisco than among IDUs within the city (Table). Odds for