Background:  The prevalence of HIV among correctional populations is many times that of the general U.S. population. Inmates in 28 state prison systems are provided voluntary (i.e. consent-based) HIV testing. The purpose of this study was to characterize the population of HIV⁺ prisoners in a state prison system with voluntary HIV testing and to estimate the number of undetected HIV cases.

Methods:  Using de-identified electronic records of adult prisoners entering the North Carolina Department of Corrections from January 2004 to May 2006, associations between HIV serostatus and conventional HIV risk behaviors, mental health, co-infection status, and sociodemographic characteristics were estimated using logistic regression. The range of undetected cases was estimated by multiplying the age-, sex-, and race-specific number of untested prisoners by corresponding stratum-specific HIV prevalence from both tested prisoners and from data for the entire state.

Results:  Approximately 40% (n = 21,419) of prisoners were tested for HIV, and nearly 3.4% (n = 718) of these tested prisoners were HIV⁺. Among men, HIV infection was most strongly associated with men who have sex with men (MSM) (OR 8.0), black race (OR 6.2), other non-white race (OR 7.4), and age 35 to 44 years (OR 4.1). The strongest risk factor among women was black race (OR 3.8). Modest associations (i.e. OR <3.0) were observed for several other risk factors across employment, education, mental health, imprisonment, drug use, and co-infection domains. Among HIV⁺ prisoners, 65% were co-infected with hepatitis C virus (HCV), >80% of HIV⁺ prisoners had been initially diagnosed with HIV before entering prison, 30% had “ever been told you have AIDS,” but fewer than half reported a conventional HIV risk behavior. We estimated between 23% (217) and 67% (1478) of HIV cases remained undetected.

Conclusions:  Modest to moderate associations and the large proportion of prisoners without reported risks highlight the potential limitations of risk factor-based HIV testing in prison. Our most conservative estimate suggests that about one-fourth of all HIV cases in the North Carolina Department of Corrections remain undetected.