Establishing HIV transmission pathways in Bhutan: a modelling study

Abstract

Background: There are limited and conflicting data regarding HIV transmission and behavioural risk factors, particularly among groups with increased risk of exposure to HIV in Bhutan. This study aims to explore comprehensive pathways to HIV infections among key populations in Bhutan.

Methods: Demographic, epidemiological, and behavioural data were collated to inform an Optima HIV model for Bhutan. The model was calibrated for a period 1990 and 2021 to align with emerging national research into risk attribution of HIV infections and behavioural dynamics of key populations. This was supplemented by qualitative feedback from stakeholder consultations throughout January-June 2022, while maintaining the consistency of the country-accepted output from the 2022 Estimation and Projection Package (EPP-Spectrum model) across all years.

Findings: In 2021, sex work was directly associated with 54% of new HIV infections. In total, 86% of new HIV infections were estimated to be among key and vulnerable populations, their direct partners, and their children. HIV prevalence remained low, ranging from 0.7% to 3.1% among key populations. Due to the relatively short duration of risk activity (average of three years among female sex workers [FSW]), only an estimated 9.7% of undiagnosed people living with HIV could be reached through interventions focused on key populations.

Interpretation: Greater efforts in developing strategies that can prevent new HIV infections among individuals currently at risk-and identifying undiagnosed HIV infections among those with historic risk who are not currently accessing HIV services-could help achieve the elimination of HIV transmission in Bhutan.

Funding: This analysis was funded through The Sustainability of HIV Services for Key Populations in Southeast Asia (SKPA-1) project, funded by the Global Fund to Fight AIDS, Tuberculosis and Malaria under agreement QMZ-H-AFAO, with Health Equity Matters as Principal Recipient. Save the Children is the sub-recipient of SKPA in Bhutan.

Keywords: Bhutan; HIV epidemiology; HIV infection; HIV transmission; Key population.

Fig. 1

Schematic diagram for process of model development and validation.

Fig. 2

Estimated new HIV infections, people living with HIV, and HIV-related deaths from 1990 to 2022. EPP-Spectrum uncertainty bounds are visualized vertically against the Optima HIV projection over time. a. Estimated new HIV infections from 1990 to 2022. b. Estimated people living with HIV from 1990 to 2022. c. Estimated HIV-related deaths from 1990 to 2022.

Fig. 3

Overview of modelled HIV prevalence, modelled HIV incidence, and total number of people living with HIV (bubble size) in 2021. Estimated people living with HIV in 2021—Female sex workers: 20; High-risk women: 14; Clients of female sex workers: 224; Men who have sex with men: 28; Men who use drugs including alcohol: 31; Transgender women: 2; Children: 32; Non-key population females: 581; Non-key population males: 394.

Fig. 4

Modes of transmission 2021 retrospective cohort analysis compared with Optima HIV model cumulative infections 1990 to 2021.

Fig. 5

Key modelled pathways to HIV infection. Thicker lines highlight primary routes of modelled transmission.