Differences in risk factors for human immunodeficiency virus type 1 seroconversion among male and female intravenous drug users.

To examine sex-specific risk factors for human immunodeficiency virus (HIV) type 1 seroconversion among intravenous drug users, the authors conducted a nested case-control study in Baltimore, Maryland, from 1988 to 1992 comparing 146 seroconverters and 539 HIV seronegative controls. Controls were matched on sex, race, date of study entry, and duration of follow-up. Risk factor data were obtained from interviews conducted at the first seroconversion visit for the case and the closest visit for the corresponding seronegative control. Since test results were not available until several weeks after interview, both interviewers and participants were unaware of seroconversion status at the time of interview. When data were analyzed using conditional logistic regression techniques, the variables which were significantly associated with seroconversion among male intravenous drug users included age less than 35 years, a sexually transmitted disease within the past 6 months, lifetime history of syphilis, and current intravenous drug use with an abscess at the injection site. Among women, only a history of three or more sex partners was positively associated with seroconversion and having a biological child under age 18 years was inversely associated with HIV seroconversion. Although the small sample size may have limited the ability to ascertain differences in risks of seroconversion among males and females, these data suggest that sexual transmission contributes to HIV infection among intravenous drug users, especially women.