Background:  Since 1987, a needle exchange program (NEP), based in the Department of Infectious Diseases, has been operating in the city of Malmö, Southern Sweden. Participants are tested approximately 3-monthly for HIV antibody, hepatitis C virus (HCV) antibody, and serologic markers of hepatitis B virus (HBV). Assessment of participants previously registered in 1990 to 1993 showed absence of HIV transmission within the NEP, but high rates of seroconversion to HCV (26.3/100 person-years at risk) and HBV (11.7/100 person-years at risk). These results led to the introduction of HBV vaccination and further education and counselling for participants. This study was performed to follow-up transmission rates of these viruses in participants registered 1995 to 2005, with a special focus on the timing of HCV transmission by combined use of antibody assays and polymerase chain reaction (PCR), and identification of risk factors for anti-HCV seroconversion.  

Methods:  Demographic data and serological test results were used to calculate seroconversion rates in susceptible subjects. From individuals who were anti-HCV negative at registration and who subsequently seroconverted to anti-HCV, HCV PCR was performed on the baseline serum sample. Fischer’s exact test, Mann-Whitney, Cox regression, and Kaplan-Meier analyses were used for statistical calculations.

Results:  Of 1661 participants, 831 were repeatedly bled, had known identities, and were included in the longitudinal study. At baseline, 830 among these were susceptible to HIV, 596 to HBV, and 332 to HCV. During 2435 person-years at risk of follow-up, the respective seroconversion rates were:  HIV 2 (0.08/100 person-years at risk); HBV 40 (3.4/100 person-years at risk); HCV 186 (38.3/100 person-years at risk). The majority (123/186, 67%) of HCV seroconversions occurred during the first year after registration. In 37 of 186 (20%) HCV seroconverters, HCV viremia was detected in the anti-HCV negative baseline sample, indicating transmission before NEP registration. After adjustment for baseline HCV viremia, the HCV incidence was 31.5/100 person-years at risk. Heroin use, incarceration prior to NEP registration, and duration of participation were associated with greater risk of HCV transmission.

Conclusions:  Although HIV incidence remained low and HBV incidence declined, HCV transmission persisted at high rates, indicating ongoing blood-borne transmission, especially during the first year after registration. HCV RNA was detected in a high proportion of subjects who were anti-HCV negative at baseline, suggesting high injecting risk behavior before joining the NEP.