Estimating the Population Size of People Who Inject Drugs in Malaysia for 2014 and 2017 Using the Benchmark-Multiplier Method

Current drug use patterns and HIV and HCV prevalence among people who inject drugs in suburban areas of Malaysia

INTRODUCTION

National surveillance data in Malaysia has observed a marked reduction in the number of new HIV cases among people who inject drugs (PWID) in the past decade. This study sought to estimate the current prevalence and associated risk factors of HIV and hepatitis C virus (HCV) among PWID in suburban areas of Klang Valley, Malaysia.

METHODS

Between September 2021 and March 2022, a cross-sectional, respondent-driven sampling survey was conducted. Participants completed rapid HIV and HCV testing as well as social and behavioural assessments. Factors associated with HIV- and HCV-positive results were estimated using logistic regression.

RESULTS

Four-hundred individuals were recruited in the study, of whom 382 (94%) were men. The prevalence of HIV and HCV was 5.5% (95% confidence interval [95% CI]: 3.6-8.3) and 40.5% (95% CI: 35.7-45.5), respectively. Current heroin and amphetamine-type stimulant (ATS) use, regardless of injection or non-injection use, were reported by 340 (85.0%) and 328 (82.0%) individuals, respectively. Past exposure to the criminal justice system (lock-ups, prison and compulsory drug detention centres) was associated with both HIV (Adjusted odds ratio [aOR] = 3.47, 95% CI: 1.33-10.2) and HCV (aOR = 3.32, 95% CI: 2.06-5.39)-positive results. Additionally, HIV-positive results were associated with current ATS use (aOR = 0.31, 95% CI: 0.12-0.86). Meanwhile, HCV-positive results were associated with current heroin use (aOR = 2.44, 95% CI: 1.16-5.48), lifetime enrolment in methadone treatment (aOR = 2.30, 95% CI: 1.23-4.27), current methadone treatment (aOR = 0.46, 95% CI: 0.23-0.92) and current mixing of drugs through injection use (aOR = 1.80, 95% CI: 1.08-3.03).

CONCLUSIONS

This study observed low HIV prevalence among PWID, primarily associated with ATS use, while HCV prevalence, linked to heroin use, remained high. Higher odds of being HCV positive among PWID who reported to have ever but not currently enrolled in methadone programmes indicate that treatment may not be continuous once initiated, potentially due to exposure to the criminal justice system. These findings underscore the need for a dual approach: enhanced harm reduction programmes for PWID and a legal reform to address potential barriers posed by criminalization.

On the estimation of population size-A comparison of capture-recapture and multiplier-benchmark methods

Approaches to population size estimation are of importance across a wide spectrum of disciplines, especially when census and simple random sampling are impractical. The capture-recapture method and the multiplier-benchmark method are two commonly used approaches that use data that partially capture the target population and overlap in a known way. Due to similarities in required data structures, the approaches are often used interchangeably without a critical appraisal of the underlying assumptions, especially in the two-sample case. Here, we describe the similarities and differences of the sampling mechanisms and assumptions underlying both approaches. We emphasize that the capture-recapture method assumes data sources as random samples and describes two-way inclusion histories, while in multiplier-benchmark method, one source captures a fixed sub-population, and the one-way inclusion histories are modeled. We also discuss the implications of these differences through simulation and real data to guide the choice of method in practice. A careful study of the data structures, relationships, and data generation processes is crucial for assessing the appropriateness of using these methods.

Assessing feasibility of a modified same-day test-and-treat model for hepatitis C among rural people who inject drugs

BACKGROUND

Despite advancements in hepatitis C virus (HCV) treatment, low uptake among hard-to-reach populations remains a global issue. The current study aimed to assess the feasibility of a modified same-day test-and-treat model in improving HCV care for people who inject drugs (PWID) living in resource-constrained rural areas.

METHODS

A pilot study was conducted in four primary healthcare (PHC) centers in Malaysia. The model's key features included on-site HCV ribonucleic acid (RNA) testing using a shared GeneXpert® system; noninvasive biomarkers for cirrhosis diagnosis; and extended care to PWID referred from nearby PHC centers and outreach programs. The feasibility assessment focused on three aspects of the model: demand (i.e., uptake of HCV RNA testing and treatment), implementation (i.e., achievement of each step in the HCV care cascade), and practicality (i.e., ability to identify PWID with HCV and expedite treatment initiation despite resource constraints).

RESULTS

A total of 199 anti-HCV-positive PWID were recruited. They demonstrated high demand for HCV care, with a 100% uptake of HCV RNA testing and 97.4% uptake of direct-acting antiviral treatment. The rates of HCV RNA positivity (78.4%) and sustained virologic response (92.2%) were comparable to standard practice, indicating the successful implementation of the model. The model was also practical, as it covered non-opioid-substitution-therapy-receiving individuals and enabled same-day treatment in 71.1% of the participants.

CONCLUSIONS

The modified same-day test-and-treat model is feasible in improving HCV care for rural PWID. The study finding suggests its potential for wider adoption in HCV care for hard-to-reach populations.

Estimating the Prevalence of Substance Use Disorders in the US Using the Benchmark Multiplier Method

Importance

Prevalence estimates of substance use disorders in the US rely on general population surveys. However, major population groups, such as homeless individuals and institutionalized individuals, are not captured by these surveys, and participants may underreport substance use.

Objective

To estimate the prevalence of substance use disorders in the US.

Design, Setting, and Participants

The benchmark multiplier method was used to estimate the prevalence of alcohol, cannabis, opioid, and stimulant use disorders based on data from the Transformed Medicaid Statistical Information System (T-MSIS) (the benchmark) and the National Survey on Drug Use and Health (NSDUH) (the multiplier) for 2018 and 2019. T-MSIS collects administrative data on Medicaid beneficiaries 12 years and older with full or comprehensive benefits. NSDUH is a nationally representative annual cross-sectional survey of people 12 years and older. Data were analyzed from February to June 2022.

Main Outcomes and Measures

Prevalence of substance use disorders was estimated using the benchmark multiplier method based on T-MSIS and NSDUH data. Confidence intervals for the multiplier method estimates were computed using Monte Carlo simulations. Sensitivity of prevalence estimates to variations in multiplier values was assessed.

Results

This study included Medicaid beneficiaries 12 years and older accessing treatment services in the past year with diagnoses of alcohol (n = 1 017 308 in 2018; n = 1 041 357 in 2019), cannabis (n = 643 737; n = 644 780), opioid (n = 1 406 455; n = 1 575 219), and stimulant (n = 610 858; n = 657 305) use disorders and NSDUH participants with 12-month DSM-IV alcohol (n = 3390 in 2018; n = 3363 in 2019), cannabis (n = 1426; n = 1604), opioid (n = 448; n = 369), and stimulant (n = 545; n = 559) use disorders. The benchmark multiplier prevalence estimates were higher than NSDUH estimates for every type of substance use disorder in both years and in the combined 2018 to 2019 sample: 20.27% (95% CI, 17.04-24.71) vs 5.34% (95% CI, 5.10-5.58), respectively, for alcohol; 7.57% (95% CI, 5.96-9.93) vs 1.68% (95% CI, 1.59-1.79) for cannabis; 3.46% (95% CI, 2.97-4.12) vs 0.68% (0.60-0.78) for opioid; and 1.91% (95% CI, 1.63-2.30) vs 0.85% (95% CI, 0.75-0.96) for stimulant use disorders. In sensitivity analyses, the differences between the benchmark multiplier method and NSDUH estimates persisted over a wide range of potential multiplier values.

Conclusions and Relevance

The findings in this study reflect a higher national prevalence of substance use disorders than that represented by NSDUH estimates, suggesting a greater burden of these conditions in the US.

Summarizing methods for estimating population size for key populations: a global scoping review for human immunodeficiency virus research

BACKGROUND

Estimating the population sizes of key populations(people who inject drugs, men who have sex with men, transgender persons, and commercial sex workers) is critical for understanding the overall Human Immunodeficiency Virus burden. This scoping review aims to synthesize existing methods for population size estimation among key populations, and provide recommendations for future application of the existing methods.

METHODS

Relevant studies published from 1st January 2000 to 4th August 2020 and related to key population size estimation were retrieved and 120 of 688 studies were assessed. After reading the full texts, 81 studies were further excluded. Therefore, 39 studies were included in this scoping review. Estimation methods included five digital methods, one in-person method, and four hybrid methods.

FINDING

We summarized and organized the methods for population size estimateion into the following five categories: methods based on independent samples (including capture-recapture method and multiplier method), methods based on population counting (including Delphi method and mapping method), methods based on the official report (including workbook method), methods based on social network (including respondent-driven sampling method and network scale-up method) and methods based on data-driven technologies (Bayesian estimation method, Stochastic simulation method, and Laska, Meisner, and Siegel estimation method). Thirty-six (92%) articles were published after 2010 and 23 (59%) used multiple methods. Among the articles published after 2010, 11 in high-income countries and 28 in low-income countries. A total of 10 estimated the size of commercial sex workers, 14 focused on men who have sex with men, and 10 focused on people who inject drugs.

CONCLUSIONS

There was no gold standard for population size estimation. Among 120 studies that were related to population size estimation of key populations, the most commonly used population estimation method is the multiplier method (26/120 studies). Every method has its strengths and biases. In recent years, novel methods based on data-driven technologies such as Bayesian estimation have been developed and applied in many surveys.