Using dual capture/recapture studies to estimate the population size of persons who inject drugs (PWID) in the city of Hai Phong, Vietnam.

BACKGROUND: Good estimates of key population sizes are critical for appropriating resources to prevent HIV infection. We conducted two capture/recapture studies to estimate the number of PWID currently in Hai Phong, Vietnam. METHODS: A 2014 respondent-driven sampling (RDS) survey served as one capture, and distribution of cigarette lighters at drug use "hotspots" in 2016 served as another "capture." A 2016 survey using RDS, conducted 1 week after lighter distribution, served as "recapture" for both captures. Recaptured participants in the two surveys were identified with a computerized fingerprint reader. Recaptured participants from the lighter distribution were asked to show their lighters. RESULTS: 1385 participants were included in the "recapture" survey. They were 94% male and had a median age of 39. All (100%) injected heroin, and HIV prevalence was 30%. 144 of the 603 participants in the 2014 survey and 152 of the 600 PWID who had received lighters were "recaptured" in the 2016 survey. After adjusting for police suppression of drug use hotspots and conducting sensitivity analyses, our best estimate of the population size from the lighter recapture was 4617 (95% CI: 4090-5143), and our best estimate from the 2014 survey recapture was 5220 (95% CI: 4568-5872). A combined best estimate of the PWID population in Hai Phong is 5000, range 4000-6000. CONCLUSIONS: The capture/recapture studies produced consistent estimates. Adding a lighter/token distribution to planned RDS surveys may provide an inexpensive method for estimating PWID population size. Analyses of the estimates should include contextual information about the local drug scene.

Prospects for ending the HIV epidemic among persons who inject drugs in Haiphong, Vietnam.

BACKGROUND: To examine the prospects for "ending the HIV epidemic" among persons who inject drugs (PWID) in Haiphong, Vietnam. Reaching an incidence of <0.5/100 person-years at risk (PY) was used as an operational definition for "ending the epidemic." METHODS: A respondent driven sampling study of 603 PWID was conducted from September to October 2014. Current heroin use (verified with urine testing and marks of injection) was an eligibility requirement. A structured questionnaire was administered by trained interviewers to obtain demographic, drug use, and risk behavior data; HIV counseling and testing and HCV testing was also conducted. Two methods (by assuming all new injectors were HIV negative at first injection and by slope of prevalence by years injecting) were used for estimating HIV among persons injecting for <5 years ("new injectors"). Comparisons were made to the HIV epidemic among PWID in New York City and modeling of the HIV epidemic in Can Tho province. RESULTS: HIV prevalence was 25% in 2014, down from 68% in 2006 and 48% in 2009; overall HCV prevalence in the study was 67%. Among HIV seropositive PWID, 33% reported receiving antiretroviral treatment. The great majority (83%) of subjects reported pharmacies as their primary source of needles and syringes and self-reported receptive and distributive syringe sharing were quite low (<6%). Estimating HIV incidence among non-MSM male new injectors with the assumption that all were HIV negative at first injection gave a rate of 1.2/100 person-years (95% CI -0.24, 3.4). Estimating HIV incidence by the slope of prevalence by years injecting gave a rate of 0.8/100 person-years at risk (95% CI -0.9, 2.5). CONCLUSIONS: The current HIV epidemic among PWID in Haiphong is in a declining phase, but estimated incidence among non-MSM new injectors is approximately 1/100 person-years and there is a substantial gap in provision of ART for HIV seropositives. Scaling up interventions, particularly HIV counseling and testing and antiretroviral treatment for all seropositive PWID, should accelerate the decline. Ending the epidemic is an attainable public health goal.