Study Design:
We implemented a cross-sectional survey among PWID using a respondent driven sampling (RDS) approach in order to compare two methods for estimating the cascade of HIV care; one based on the results of self-report of HIV care, and the second based on an objective marker of HIV care. For the latter, we selected the detection of lamivudine in plasma because this drug composed both the first line and the second-line of HIV treatment in Vietnam at the time of the study.
Study implementation and flow:
We recruited ‘active’ PWID using an RDS survey in Hai Phong, Vietnam, during September and October 2014, using the following inclusion criteria: (i) reporting injection drug use and having recent skin marks of injection, (ii) having drug detected in urine (heroin or methamphetamine) and (iii) able and willing to provide informed consent. Details of the RDS survey have been described elsewhere [2, 16]. The study took place in a community setting, in the office of a major peer support group of the city. A standardized questionnaire was administered by a trained interviewer selected from three community support groups. This questionnaire addressed issues on participant’s drug use, sexual behaviors, medical and administration-related events (arrests, etc.). A venous sample was taken by a nurse on site for HIV testing (Determine™ HIV-1/2, Alere™, Waltham, USA) and plasma biobanking. Participants returned to the study site one week later for their HIV test result confirmation which was done at the provincial AIDS center laboratory. HIV viral load was measured on the banked blood sample at the national reference laboratory (NIHE, Hanoi) using the COBAS Taqman HIV-1 test v2.0 (Roche diagnostics, Hanoi, Vietnam).
Plasma lamivudine (3TC) quantification:
After alcaline extraction from stored plasma sampled, lamivudine was detected using high pressure liquid chromatography with ultraviolet detection as previously described [17]. The lower limit of detection of the assay was set at 25ng/ml of plasma, lower than 40ng/ml, the mean trough concentration at steady state before once daily lamivudine intake (300mg).
Data Collection & data analyses:
All data were collected through electronic CRF using Ennov Clinical® software.
Baseline characteristics of participants were presented using number and percentage for categorical data; and median and interquartile range (IQR) for quantitative variables.
The usual cascade of care was constructed as follows: the denominator was all HIV-infected PWID, self-declaration was used to estimate the proportion of HIV-infected PWID aware of their HIV status, and of those with efficacious ART defined by a plasma viral load <1,000 copies/mL as per WHO recommendations [18].
For the construction of the improved cascade, we assumed that HIV-infected PWID with detectable lamivudine in plasma were aware of their HIV status, whatever their responses to the questionnaire.
All statistical analyses were done with SAS software (Version 9.4; Copyright© 2016, SAS Institute Inc., Cary, NC, USA).