Mapping and population size estimates of people who inject drugs in Afghanistan in 2019: Synthesis of multiple methods.

Introduction: Mapping and population size estimates of people who inject drugs (PWID) provide information needed for monitoring coverage of programs and planning interventions. The objectives of this study were to provide the locations and numbers of PWID in eight cities in Afghanistan and extrapolate estimates for the country as a whole.

Methods: Multiple population size estimation methods were used, including key informant interviews for mapping and enumeration with reverse tracking, unique object and service multipliers, capture-recapture, and wisdom of the crowds. The results of the several methods were synthesized using the Anchored Multiplier-a Bayesian approach to produce point estimates and 95% credible intervals (CI). Using the prevalence of PWID in the eight cities and their correlation with proxy indicators, we extrapolated the PWID population size for all of Afghanistan.

Results: Key informants and field mapping identified 374 hotspots across the eight cities from December 29, 2018 to March 20, 2019. Synthesizing results of the multiple methods, the number of male PWID in the eight study cities was estimated to be 11,506 (95% CI 8,449-15,093), corresponding to 0.69% (95% CI 0.50-0.90) of the adult male population age 15-64 years. The total number of women who injected drugs was estimated at 484 (95% CI 356-633), corresponding to 0.03% (95% CI 0.02-0.04) of the adult female population. Extrapolating by proxy indicators, the total number of PWID in Afghanistan was estimated to be 54,782 (95% CI 40,250-71,837), men and 2,457 (95% CI 1,823-3,210) women. The total number of PWID in Afghanistan was estimated to be 57,207 (95% CI 42,049-75,005), which corresponds to 0.37% (95% CI 0.27-0.48) of the adult population age 15 to 64 years.

Discussion: This study provided estimates for the number of PWID in Afghanistan. These estimates can be used for advocating and planning services for this vulnerable at-risk population.