Female sex workers (FSW) face intersecting individual, interpersonal, and structural challenges that exacerbate risk to their health and wellbeing [1]. At the macro-structural level, FSW experienced economic vulnerability, housing instability [2], [3], mobility [1], [4], stigma [1], [5], and criminalization [1], [2], [5], which restrict their rights and power. In their community, FSW face violence [2], [6], [7] and police abuse [2]. Many FSW have mental health stressors with significant risk of self-harm and suicide [2], [6]. Reported alcohol and substance use is prevalent [2], [3], [7], [8]. Moreover, FSW have an estimated 30 times increased risk of acquiring HIV versus other reproductive-aged women [5]. Because of these multifactorial barriers, FSW with HIV often struggle to adhere to ART, remain in care, and virally suppress [9]. There were an estimated 146,000 FSW in South Africa in 2021 [5], with an HIV incidence of 5 infections per 100 person-years [10] and HIV prevalence of 60% [10], [11]. Only 70% of FSW with HIV in South Africa were reported to be using ART [11], which indicates suboptimal care coverage and heightened risks of HIV-associated morbidity and mortality. Among people with HIV (PWH), tuberculosis (TB) and cryptococcal meningitis are major causes of AIDS-related deaths [5]. A recent study conducted in multiple countries, including South Africa, reported abortions, suicides, and murders as the leading causes of death among FSW [12]. However, mortality among FSW remains understudied due to the lack of methodology to comprehensively capture vital status and the reported mortality among FSW may miss a significant number of deaths due to loss to follow-up (LTFU).

High LTFU has been reported among FSW in both study and care settings. Specifically, 33% of FSW became LTFU in a 5-year HIV incidence cohort conducted in Zambia [13], and 27-55% of FSW with HIV in routine care in Côte d'Ivoire and Uganda became LTFU within 24 months [9], [14]. Busy work schedules [15], travel [15] or migration for sex work and economic opportunities [4], and working on the street with unstable [15] or lack of phone ownership [9] may challenge engagement in research and HIV care. However, LTFU may mean silent transfer (i.e., the participants transfer to receive HIV care at a new facility without documentation at the previous facility), disengagement from care, or undocumented death [16], [17], [18]. If PWH become disengaged from care, they may have poor ART adherence and high viral load (VL), resulting in an increased risk of mortality [19]. Systematic reviews of tracing studies across Sub-Saharan Africa reported a wide range between 9-87% of LTFU PWH had actually died [19], [20], [21]. Understanding the factors associated with LTFU can help program implementers identify better strategies to facilitate retention. Accounting for LTFU may improve assessments of mortality and other health outcomes, which are necessary to inform improved programs and policies.

This study aims to determine factors associated with LTFU and estimate mortality risk of FSW with an unsuppressed HIV VL in Durban, South Africa, from 2018-2021, in a context of an implementation trial.