HIV incidence among injection drug users in Baltimore, Maryland (1988-2004).

BACKGROUND: We examined recent trends (1999-2004) in HIV incidence among a cohort of injection drug users (IDUs) followed since 1988 in Baltimore, Maryland.
METHODS: One thousand eighty-three HIV-seronegative individuals with a history of injection drug use were recruited between 1988 and 1998 and returned for >or=1 semiannual follow-up visit, where they underwent HIV antibody testing and interviews eliciting risk behaviors. Person-time methods were used to calculate HIV incidence rates per 100 person-years (PYs).
RESULTS: Over 14,770 PYs, 304 individuals seroconverted to HIV (2.06 per 100 PYs). Annual incidence declined from 4.57 in 1988 to 0.53 per 100 PYs in 2004. Similarly, among individuals actively injecting drugs, incidence steadily declined from 5.43 in 1988 to 0 in 2004, with the exception of 2003, when an incidence of 2.59 per 100 PYs was observed. Reported sexual risk behaviors and drug injection declined from 1988 through 2004, but among those actively injecting, reported needle sharing declined from 1988 through 1998 and then increased from 30% in 1998 to nearly 40% in 2003 through 2004.
CONCLUSIONS: Long-term declines in HIV incidence among IDUs are consistent with other reports; however, in 2003, we observed an unexpected increase in seroconversion that seems to be related to needle sharing. Although additional follow-up is needed to identify trends, these data indicate the need to reinforce HIV prevention efforts and to continue surveillance of drug users' behaviors.