Hepatitis C incidence--a comparison between injection and noninjection drug users in New York City.

Hepatitis C virus (HCV) burdens injection drug users (IDUs) with prevalence estimated from 60-100% compared to around 5% among noninjection drug users (non-IDUs). We present preliminary data comparing the risk for HCV among IDUs and non-IDUs to inform new avenues of HCV prevention and intervention planning. Two cohorts, new IDUs (injecting < or =3 years) and non-IDUs (smoke/sniff heroine, crack or cocaine < or =10 years), ages 15-40, were street-recruited in New York City. Participants underwent risk surveys and HCV serology at baseline and 6-month follow-up visits. Person-time analysis was used to estimate annual HCV incidence. Of 683 non-IDUs, 653 were HCV seronegative, 422 returned for at least 1 follow-up visit, and 1 became HCV seropositive. Non-IDUs contributed 246.3 person-years (PY) yielding an annual incident rate of 0.4/100 PY (95% Confidence Interval [CI]=0.0-1.2). Of 260 IDUs, 114 were HCV seronegative, 62 returned for at least 1 follow-up visit, and 13 became HCV seropositive. IDUs contributed 36.3 PY yielding an annual incidence rate of 35.9/100 PY (95%CI=19.1-61.2). Among IDUs, HCV seroconverters tended to be younger (median age 25 vs. 28, respectively), and inject more frequently (61.5% vs. 34.7%, respectively) than non-seroconverters. These interim data suggest that IDUs may have engaged in high-risk practices prior to being identified for prevention services. Preventing or at least delaying transition into injection could increase opportunity to intervene. Identifying risk factors for transition into injection could inform early prevention to reduce onset of injection and risk of HCV.