Trends in human immunodeficiency virus seroincidence among street-recruited injection drug users in San Francisco, 1987-1998.

This paper reports trends in human immunodeficiency virus (HIV) incidence among street-recruited injection drug users (IDUs) in San Francisco, California, from 1987 through 1998, estimated using a sensitive/less sensitive enzyme immunoassay testing strategy. IDUs were enrolled in 23 semiannual cross-sections from three community sites. For identification of recent infections, less sensitive enzyme immunoassay testing was performed on stored specimens that had previously tested positive for HIV antibodies. Annualized incidence rates were calculated and logistic regression models were fitted for assessment of risk factors for recent HIV infection. Among 8,065 susceptible IDUs, 34 had recent infections, for an incidence rate of 1.2% (95% confidence interval: 0.7, 2.0) per person-year. This rate declined from 2.7% in 1987/1988 to approximately 1% per person-year between 1989 and 1998. Two IDU subpopulations were at highest risk for infection: persons under age 30 years (2.8% per person-year) and men who had sex with men (3.0% per person-year). Participants who reported prior HIV test-result counseling were less likely than others to become infected (adjusted odds ratio = 0.43, 95% confidence interval: 0.21, 0.87). Sensitive/less sensitive enzyme immunoassay testing is an effective tool for assessing HIV incidence. HIV incidence among street-recruited IDUs in San Francisco appears to have remained stable and moderate since the late 1980s.