Sex differences in risk factors for HIV seroconversion among injection drug users -: A 10-year perspective

Background: Injection drug use directly or indirectly accounts for nearly half the annual human immunodeficiency virus (HIV) infections in the United States. Prospective studies that investigate both sexual and parenteral HIV risks among injection drug users (IDUs) are needed. We studied factors for HIV seroconversion among male and female IDUs in Baltimore, Md. Methods: The HIV-negative IDUs (1447 male and 427 female) were recruited into a prospective study from 1988 to 1989 or in 1994. Participants underwent semiannual HIV tests and surveys through December 1998. Poisson regression was used to identify risk factors for HIV seroconversion, stratified by sex. Behaviors were treated as time-dependent covariates that varied at each semiannual period. Results: Subjects were primarily African American (91%), and median age at enrollment was 35 years. Incidence of HIV was 3.14 per 100 person years (95% confidence interval, 2.78-3.53) and did not significantly differ by sex. Younger age independently predicted HIV seroconversion for both men and women. Among men, factors that independently predicted HIV seroconversion were the following: less than a high school education, recent needle sharing with multiple partners, daily injection, and shooting-gallery attendance. The incidence of HIV was double for men recently engaging in homosexual activity and cocaine injection. Among women, the incidence of HIV was more than double for those recently reporting sexually transmitted diseases. Conclusions: The incidence of HIV remained high among IDUs in Baltimore over the past decade. Risk factors for HIV seroconversion differed markedly by sex. Predominant risks among men included needle sharing and homosexual activity; among women, factors consistent with high-risk heterosexual activity were more significant than drug-related risks. Human immunodeficiency virus interventions aimed at IDUs should be sex-specific and incorporate sexual risks.