HIV seroconversion in intravenous drug users in San Francisco, 1985-1990.

OBJECTIVE

To examine the HIV seroconversion rate, risk factors for seroconversion, and changes in risk behavior over time in intravenous drug users (IVDU) in San Francisco, 1985-1990.

DESIGN

Observational study.

SETTING

All methadone maintenance and 21-day methadone detoxification programs in San Francisco.

PARTICIPANTS

A total of 2351 heterosexual IVDU, of whom 681 were seronegative at first visit and seen at least twice ('repeaters').

MAIN OUTCOME MEASURES

HIV seroconversion rates, risk factors for seroconversion, and changes in behavior.

RESULTS

The HIV seroconversion rate in repeaters was 1.9% per person-year (ppy) of follow-up [2.1% in women versus 1.7% in men (not significant); 4% in African Americans versus 1% in whites (P = 0.006); 3.9% ppy in the first third of the study, 1.2% in the second (P = 0.007), and 1.9% in the last (not significant)]. Risk factors for seroconversion were five or more sexual partners per year [hazard ratio (HR) = 2.6; P = 0.02], use of shooting gallery ever (HR = 2.9; P = 0.02), and less than 1 year (lifetime) in methadone maintenance (HR = 2.7; P = 0.02). Self-reported intravenous cocaine use fell from 33 to 15% over 5 years, shooting gallery use fell from 19 to 6%, and the proportion with five or more sexual partners fell from 25 to 10%. Bleach use rose to 75% of needle-sharers.

CONCLUSIONS

The 1985-1990 HIV seroconversion rate in IVDU (1.9% ppy) was comparable to that in San Francisco cohorts of homosexual men (1.4% ppy). A decline in HIV seroconversion coincided with changes in risk behavior. Stable attendance of methadone maintenance was highly protective: the seroconversion rate in subjects with 1 year or more in methadone was 12% ppy.