Seroconversion issues among out-of-treatment injection drug users

Many risk factors for HIV incidence among drug users have been reported in the literature. However most of these studies have been with local samples, and typically have had limited sample sizes. The National Institute on Drug Abuse (NIDA) funded a Cooperative Agreement for AIDS Community-Based Outreach/Intervention Research (CA) since 1991 that produced a national database. Associations found in the literature were tested to determine whether they were replicated on this national database. The CA national database had complete data, including blood draws six months apart, on 6,970 drug users who were seronegative at baseline. Sites that had no seroincident cases were excluded from the analysis. Twenty-nine risk factors identified in the literature were tested on the national database on a bivariate basis. There were 56 seroincident cases (those who were HIV-seronegative at baseline and HIV-seropositive at follow-up) out of 3752 person years at risk, for a seroconversion rate of 1.49 (CI 1.05, 1.94) per 100 person years at risk. Data were analyzed both as a whole dataset and with the sites stratified by high and low prevalence. In the overall analysis, risk factors associated with seroconversion were times injected any drug, ever injected any drug, days injected cocaine, times injected cocaine, and times injected speedball (these variables had a 30-day time referent). Also significant was how recently formerly-used injection equipment was used. High-prevalence sites revealed associations for times injected any drug, days injected cocaine, and times injected speedball. Low-prevalence sites revealed associations for injected any drug and days injected cocaine. These findings highlight the importance of injection drug use, especially cocaine injection, as a major risk factor in recent seroconversion.