Understanding heterogeneity in HIV transmission dynamics among key populations at highest risk of acquisition

Abstract

The HIV epidemic in Pakistan is most concentrated among key populations (KPs): people who inject drugs (PWIDs) and sex workers (SWs), with the epidemic largely driven by PWIDs. A significant proportion of SWs have overlapping risks due to their interaction with PWIDs through sexual and/or drug injecting networks, thus augmenting their own risk of HIV acquisition. As a result, there is a growing concern that the epidemic in Pakistan will increase substantially among SWs due to their interaction with PWIDs, and perhaps with increasing sexual transmission to the general population through their sexual clients. However, little is known about regional disparities in the trends and patterns of HIV transmission dynamics among KPs in Pakistan. The overall goal of this research was to investigate the dynamic interplay among KPs in Pakistan in order to improve our understanding of heterogeneity in the emergence, persistence, and spread of HIV infection. Combined with epidemiological analyses, mathematical modeling methods were utilized to explore the complex social and sexual interactions among KPs to elucidate pathways leading to heterogeneity in HIV transmission dynamics. In addition to data from mapping, four rounds of cross-sectional biological and behavioral surveillances data of KPs collected from 20 cities in Pakistan between 2005-2011 were used for analyses. This research revealed that the HIV epidemic in Pakistan is immensely heterogeneous, comprised of multiple sub-epidemics among KPs, and with substantial variation in geographical trends. Social and sexual networking between SWs and PWIDs may play a key role in the emergence, persistence and spread of HIV among SWs. Findings suggested that there was up to a 3-fold difference in drug injecting probability among SW groups, dependent on where and/or how the SW solicited sexual clients. Nearly one-in-five infections among SWs in Pakistan are estimated to be attributed to sexual transmission from PWIDs; however, results vary substantially by region. The incidence rate among SWs is projected to continue to rise through 2020, while it reached peak among PWIDs in 2011. This research provided key information that can be used for: national and regional level target setting and resource mobilization, geographical prioritization of HIV response, local level programme planning, target setting and monitoring, and advocacy.