Using IBBS Survey Data and Stakeholder Consensus to Estimate Population Size of Female Sex Workers in Three South African Cities: Results and Recommendations From the 2013-14 South Africa Health Monitoring Survey (Preprint)
Authors: Grasso Michael A , Manyuchi Albert E , Sibanyoni Maria , Marr Alex , Osmand Tom , Isdahl Zachary , Struthers Helen , McIntyre James A , Venter Francois , Rees Helen V , Lane Tim 
Published: March 2018

BACKGROUND

Robust population size estimates (PSEs) for female sex workers (FSW) and other key populations in South Africa face multiple methodological limitations, including inconsistencies in surveillance and programmatic indicators; this has consequently challenged appropriate allocation of resources and benchmark-setting necessary to an effective HIV response. A 2013-14 Integrated Biological and Behavioral Surveillance (IBBS) survey from South Africa showed alarmingly high HIV prevalence among FSW in South Africa’s three largest cities of Johannesburg (71.8%), Cape Town (39.7%), and eThekwini (53.5%). The survey also included several multiplier-based population size estimation (PSE) methods.

OBJECTIVE

To present the selected PSE methods used in an IBBS survey and subsequent participatory process used to estimate the number of FSW in three South African cities.

METHODS

In 2013-14 we used respondent driven sampling (RDS) to recruit independent samples of FSW for IBBS surveys in Johannesburg, Cape Town, and eThekwini. We embedded multiple multiplier-based PSE methods into the survey, from which investigators calculated a range of PSEs for each city’s FSW population. Following data analysis, investigators consulted civil society stakeholders to present survey results and PSEs and facilitated stakeholder vetting of individual PSEs to arrive at consensus point estimates with upper and lower plausibility bounds.

RESULTS

A total of 2,180 FSW participated in the SAHMS survey. To perform the size estimate exercise, investigators calculated preliminary point estimates as the median of the multiple estimation methods embedded in the IBBS survey, and presented these to a civil-society convened stakeholder group. Stakeholders vetted all estimates in light of other data points, including programmatic experience, to ensure that only plausible point estimates were included in the calculation of the median. After vetting, stakeholders adopted three consensus point estimates with plausible ranges (PR): Johannesburg 7,697 (plausible range (PR) 5,000 - 10,895); Cape Town 6,500 (PR 4,579-9,000); eThekwini 9,323 (PR 4,000-10,000).

CONCLUSIONS

Through the use of several PSE methods embedded in an IBBS survey and a participatory stakeholder consensus process, SAHMS produced FSW size estimates representing approximately 0.48%, 0.49% and 0.77% of the adult female population in Johannesburg, Cape Town and eThekwini. In data-sparse environments, stakeholder engagement and consensus is critical to vetting of multiple empirically-based PSE procedures to ensure adoption and utilization of data-informed PSEs for coordinated national and sub-national benchmarking. Incorporating stakeholder consensus in PSE methodology has the potential to increase coherence in national and key populations-specific HIV responses, and decrease the likelihood of duplicative and wasteful resource allocation. We recommend building cooperative and productive academic-civil society partnerships around PSE and other strategic information dissemination and sharing to facilitate the incorporation of additional data as it becomes available in order to increase accuracy and precision over time, and decrease biases inherent in any single, investigator calculated method.