Sexual Transmission of HIV-1 Among Injection Drug Users in San Francisco, USA

BACKGROUND: Many new HIV-1 infections in the USA occur in injection drug users (IDUs). HIV-1 seroconversion of IDUs is mainly associated with injection-related risk factors. Harm reduction programmes concentrate on injection-risk behaviour. The authors aimed to establish whether injection or sexual risk factors, or both, were associated with HIV-1 antibody seroconversion of street-recruited IDUs in San Francisco, from 1986 to 1998. METHODS: IDUs were enrolled every 6 months from four community sites. The authors did a nested case control study comparing 58 respondents who seroconverted between visits with 1134 controls who remained seronegative. Controls were matched with cases by sex and date. Adjusted odds ratios and 95% CI were calculated for men and women by use of conditional logistic regression. FINDINGS: Men who had sex with men were 8.8 times as likely to seroconvert (95% CI 3.7-20.5) as heterosexual men. Women who reported having traded sex for money in the past year were 5.1 times as likely as others to seroconvert (95% CI 1.9-13.7). Women younger than 40 years were more likely to seroconvert than those 40 years or older (2.8 [1.05-7.6]), and women who reported having a steady sex-partner who injected drugs were less likely to seroconvert than other women (0.32 [0.11-0.92]). INTERPRETATION: HIV-1 seroconversion of street-recruited IDUs in San Francisco is strongly associated with sexual behaviour. HIV-1 risk might be reduced by incorporation of innovative sexual-risk-reduction strategies into harm-reduction programmes.