Estimating the Size of Most-at-Risk Populations for HIV/AIDS Using the Generalized Network Scale-Up Method: A Study in Shiraz, IranIran

Accurate estimation of the sizes of most-at-risk populations (MARPs) for HIV infection is critical for effective intervention planning, resource allocation, and service coverage assessment. This study aimed to estimate the population sizes of female sex workers (FSWs), people who inject drugs (PWIDs), and men who have sex with men (MSM) in the 18-45-year-old population of Shiraz, Iran, using the network scale-up (NSU) method. A cross-sectional study was conducted involving 768 purposively selected individuals aged 18-45 years residing in Shiraz for at least 5 years. Data were collected through a self-administered questionnaire, utilizing 16 reference groups with known frequencies to estimate average social network size. The prevalence of MARPs was then estimated and adjusted using established correction factors. The average active social network size was 203 contacts (103 males and 100 females). Adjusted size estimations indicated the highest prevalence among FSW at 2,181 per 100,000 (95% confidence interval [CI]: 1,979-2,375), followed by PWID at 561 per 100,000 (95% CI: 488-633) and MSM at 418 per 100,000 (95% CI: 272-563). Age distribution analyses revealed the greatest PWID prevalence in the 35-39 age group, FSW in 30-34, and MSM in 25-29. The estimated sizes of these populations substantially exceeded current harm-reduction program coverage in the region. Application of the NSU method revealed significant gaps between the actual sizes of high-risk populations and those reached by existing interventions in Shiraz. Targeted expansion of prevention, testing, and treatment programs, alongside initiatives to combat stigma and improve outreach, is urgently needed to control HIV transmission among these hidden and vulnerable groups.