Key risk factors for substance use among female sex workers in Soweto and Klerksdorp, South Africa: A cross-sectional study.

INTRODUCTION: Sex workers in South Africa experience high levels of trauma and mental health issues, but little is known about their drug and alcohol use. This study assessed the prevalence of substance use and its key risk factors amongst female sex workers (FSWs) at two sites in South Africa.
METHODS: Two cross-sectional studies were conducted, in Soweto and Klerksdorp, South Africa. Using respondent-driven sampling (RDS) 508 FSWs in Soweto and 156 in Klerksdorp were enrolled. A study-specific survey was used to collect social and demographic information, substance use, mental ill-health, and HIV status. Raw and RDS-adjusted data were analyzed using Chi-squared tests of association. Weighted and unweighted Poisson regression models were used to assess key risk factors for alcohol and drug use at both univariate and multivariate levels.
RESULTS: Of the 664 FSWs, 56.2% were binge drinkers and 29.4% reported using drugs within the last year. Living in a home with regular food (RR: 1.2597, 95% CI: 1.1009-1.4413) and being HIV positive (RR: 1.1678, 95% CI: 1.0227-1.3334) were associated with a higher risk of binge drinking. Having symptoms suggestive of post-traumatic stress disorder (RR: 1.1803, 95% CI: 1.0025-1.3895) and past year physical/sexual abuse from either intimate (RR: 1.3648, 95% CI: 1.1522-1.6167) or non-intimate partners (RR: 1.3910, 95% CI: 1.1793-1.6407) were associated with a higher risk of drug use. DISCUSSION: In conclusion, our findings demonstrate a high prevalence of alcohol and drug use among FSWs in Soweto and Klerksdorp with site-specific contextual dynamics driving substance use. Site differences highlight the importance of tailoring site-specific substance use harm mitigation for this key population.

Introduction

South Africa has one of the highest levels of alcohol consumption per adult drinker, globally [1]. While women generally drink less alcohol than men [2], female sex workers (FSWs) have been found to have a greater likelihood of a past year diagnosis of substance use disorder compared to women who do not sell sex [3]. Based on a review of global literature, 19–76.5% of FSWs use alcohol prior to and during sex work. The large range demonstrates that levels of alcohol use vary widely, and this is likely a consequence of cultural and other environmental factors [4].

A high proportion of FSWs in South Africa have been described as engaging in hazardous alcohol consumption, defined as scoring 3 or higher on the AUDIT-C scale of 0–12 [5]. For example, 81.5% of FSW in Johannesburg, 58.4% in Cape Town, 43.0% in Durban [6], and 84.8% in Soweto [7] were classified as hazardous drinkers. There are no previously reported rates of binge drinking available specifically for the South African FSW population, though a Kenyan study reports that 33% of the study’s FSW population were binge drinkers [8]. In addition to alcohol, studies have shown a high prevalence of substance use (alcohol and other drug use) amongst sex workers, both globally and in South Africa [9, 10]. A 2015 study of FSWs in KwaZulu-Natal found that 83.2% of respondents admitted to lifetime substance use [11]. Across the country, the use of opioids such as heroin, codeine, and Nyaope (antiretroviral therapy [ART] medication mixed with detergent, rat poison, marijuana, and/or methamphetamine) has been increasing [12, 13]. Alcohol and other drugs have been widely used by both FSWs and their male clients to facilitate participation in sex work [3, 4, 9]. Evidence suggests that taking substances may act as a coping strategy for stress resulting from stigma, violence, and/or emotional trauma [4, 14, 15].

In South Africa, the lifetime prevalence of substance use disorders among adults is 13.3%, and yet less than 5% ever receive treatment [16]. Women are significantly underrepresented in substance use treatment facilities, comprising only 10–24% of treatment centre patients across all nine South African provinces [17, 18]. One study of women in Pretoria showed that less than 20% of participants had any awareness of existing alcohol and drug treatment programmes [3]. There are no substance treatment centres dedicated to FSWs despite the high prevalence of substance use in this population, and access to the few treatment centres is limited, partially due to the limited availability of space and services [3, 19, 20]. Most treatment centres are unable to address gender and work-specific needs of FSW, such as childcare, trauma, and competing financial priorities, since these women cannot earn an income while in treatment. These barriers make services even more inaccessible to FSW most at need for support [3, 21, 22]. FSWs often face discrimination in public facilities due to the criminalisation of sex work [7, 13], which consequently reduces their access of health care.

FSWs have been found to experience overall higher levels of childhood trauma according to the childhood trauma questionnaire [23, 24] and of recent exposure to violence in comparison to the general population [25, 26]. A 2015 study assessing polyvictimisation of FSWs in Soweto, South Africa found higher levels of childhood trauma amongst FSWs compared to the general population, and this vulnerability continued into adulthood (25). Almost 86.6% of FSWs reported experiencing some form of violence in their lifetime [25]. The increased prevalence of substance use that FSWs face may account for the higher prevalence of mental health issues compared to the general population [11]. Findings from previous research highlight a high prevalence of depressive symptoms amongst FSWs, with more than two thirds of FSWs in Soweto experiencing symptoms suggestive of severe depression, and more than a third suggestive of post-traumatic stress disorder (PTSD) [7].

Mental health disorders and exposure to violence have both been associated with substance use disorder [27, 28]. Excessive drinking is a maladaptive coping strategy, and can be used to mask underlying mental health concerns such as depression and PTSD [4, 29]. High levels of alcohol consumption are a contributing factor for risky sexual behaviours and HIV acquisition among women in South Africa [30]. Furthermore, depressive symptoms, violence, and substance use are all associated with a poor adherence to ART among people living with HIV infection [11, 31, 32]. Given the goal to achieving the United Nations 95:95:95 targets by 2030 [33], and in a key population where HIV prevalence has been recorded to range between 34–90%, factors influencing poor adherence to ART can be problematic and directly impact viral suppression [6, 24, 34, 35].

Despite the high prevalence of trauma and mental health concerns reported by FSWs in South Africa, gaps exist when focusing on patterns of substance use for this population. We describe the prevalence of self-reported substance use (i.e.; binge drinking and drug use) and associated risk factors among FSW populations from Soweto and Klerksdorp, South Africa.

Methods

Study design, setting and sampling

Two separate cross-sectional studies were conducted, first in Soweto and then in Klerksdorp, South Africa. The two studies used the same respondent driven sampling (RDS) methodology, where an initial respondent is recruited based on network size, issued with coupons and asked to invite additional participants from within their network. Respondent driven sampling is frequently used to enroll hard to reach populations for population-level estimates [36, 37]. In Soweto, 508 FSW were recruited between February and September 2016 [38]. The methodology from the Soweto study has been thoroughly described in previous publications [7]. A replica RDS study was undertaken in Klerksdorp in 2018, enrolling 156 FSW. The sample sizes across both studies were based on an estimated number of FSW for each geolocation alongside respective HIV prevalence estimates [7].

Soweto is a predominantly urban and peri-urban, low-income township on the outskirts of Johannesburg, South Africa. It has the highest population density in South Africa, with over a million inhabitants [39]. Soweto has approximately 3,000 drinking establishments (legal and illegal), with over R50 million (USD 3.8 million) spent annually on beer [24]. Sex work is often undertaken informally within drinking establishments, in private homes, and in open spaces, with few formal brothel or strip-club type venues. While FSW report having between 0–19 clients per day, informal sex work was also paid for in beer [24]. Klerksdorp is a gold and platinum mining town in the Matlosana Municipality in the Dr Kenneth Kaunda district, North West Province, made up of peri-urban townships. The district is home to almost two hundred thousand inhabitants. Sex work is common within mining and trucking communities [40-42], however little was known about this population of FSW.

Accessing FSW populations poses unique and often challenging ethical concerns. Sex workers in South Africa are vulnerable due to the stigma associated with the work, the high levels of violence, and ongoing criminalisation of sex work. For this reason it is imperative to ensure the protection of participants from any harm (whether it be physical, emotional, legal, social or psychological) during the research. For both studies, data collection teams worked closely with local sex work program implementing partners to ensure that access to the sex work population was rapid, trust could be quickly earned, and effective linkage to care and follow-up for health or human rights concerns could be addressed. Sex work programs have been strategically designed to provide and facilitate rights-based access to healthcare as well as psychosocial and risk reduction services catering specifically to the needs of sex workers. By utilizing peer educators and an outreach model, the programs provide HIV Testing Services (HTS) and linkage to care, and widespread condom and lubricant distribution and are considered as pillars of public health care in the sex work sector.

Study participants inclusion criteria

Across both sites, eligible participants were cisgender female, aged 18 years or older, sold sex within the past 6 months in the respective district, possessed a study specific and valid recruitment coupon (see below section), and gave voluntary informed consent to participate.

Recruitment, screening and enrollment

A total of 11 seeds (initial participants) in Soweto and two seeds in Klerksdorp were used to initiate recruitment at each location. Seeds were identified by other FSWs as well-networked FSWs within their community during their monthly workshop sessions in the local sex work program. Seeds were selected based on the size of their network of FSWs in the sub-district (other FSWs they knew and had seen within the preceding two weeks). Similar to a chain referral method [36], all participants (including seeds) were given a maximum of three coupons with which to recruit additional potential participants. Seeds and subsequently enrolled participants were asked to give the coupons at random to women they knew and who knew them, who (like themselves) sold sex in the recruitment geolocation and who were 18 years or older. Potential participants with coupons arrived at the two sites for screening and enrolment procedures, including written informed consent to participate in the study, administered by sex worker peer educators in either English, isiZulu, Sesotho or Setswana.

Data collection and management

Post enrollment, a 45-minute, interviewer-administered questionnaire was completed. Interviews were conducted in a private location and data was collected in real time onto tablets using the REDCap electronic data management system [43]. REDCap databases were designed with built-in skip patterns and algorithms and were monitored daily to ensure data quality. Participants were reimbursed for their time (250 ZAR; $19 USD), and a secondary incentive (20 ZAR; $1.5 USD) for successful chain-recruitment was provided 7–10 days later. Data were captured directly onto tablets using the REDCap electronic data management system [43], with built-in skip patterns and algorithms and monitored daily to ensure data quality. RDS assumptions [36, 37] were monitored during data collection, using specialist software (RDS-Analyst) [44].

Questionnaire and study measures

The initial questionnaire was developed for the Soweto study using a community centric approach, and subsequently used for the Klerksdorp study (S1 Questionnaire). In adapting to the findings of the Soweto study and Klerksdorp contextual factors, the Center for Epidemiologic Studies Depression Scale (CES-D) short depression scale was used [45]. The questionnaire is comprised of a number of tools that have been previously validated (S1 Table). Workshops with FSW and peer educators at both sites were undertaken to obtain input and feedback on the study design and questionnaire. Cognitive interviews, to assess whether the questionnaire was understandable, appropriate, and colloquially suitable were conducted with FSW to improve the reliability of the questionnaire.

Socio-demographics

The socio-demographic data collected included age; migration status (local vs internal [South African] immigrant vs external [cross-border] immigrant based on birthplace); highest level of education; food security (do people in your home go regularly without food?); and sexual history, including age of sexual debut, circumstances of first sex (coercive: ‘I was tricked/forced/raped’ vs non-coercive: ‘I was willing/was persuaded’), and age first sold sex.

HIV status and treatment

HIV status was determined by two concurrent rapid tests (Abon™ and First Response™). HIV positive participants self-reported ART use (never taken treatment vs on treatment always vs stopped taking treatment [defaulted]). Participants on ART self-reported their adherence, with adherence defined as either always being on treatment or having taken treatment between 5–7 days in the past week and non-adherence defined as having taken treatment less than 5 days in the past week. South Africa’s ART policy had evolved numerous times prior and during the two study enrolment periods. At the time that the Soweto study was enrolling participants, adults with a CD4 count of <500 cells/mm3 were eligible to initiate treatment [46]. However, universal test and treat (UTT) was introduced in South Africa on 1 September 2016, thus making ART available to all HIV infected persons regardless of CD4 count [47] and same day ART initiation came into effect from 1 September 2017 [48].

Mental health, experienced trauma, and substance use

Depression was measured using the 10-item CES-D short scale [45]. Depression scores were calculated and a cut-off of 9 was used to indicate major depressive symptoms. Questions included ‘During the past week I was worried by things that usually don’t worry me’, and ‘During the past week I felt I was just as good as other people’. Responses ranged from: 0 ‘rarely/none of the time’, 1 ‘some of the time (1-2days)’, 2 ‘a moderate amount of time (2–4 days)’ and 3 ‘most of the time (5–7 days)’. Scores were tallied and the overall scale alpha was 0.68.

Post-traumatic stress disorder was measured using the PTSD-8 scale [49]. Questions were categorised into three subscales in line with the DSM-IV [49] (hypervigilance, intrusion and avoidance). Participants were asked 8 questions referring to having ‘recurrent thoughts or memories of the event’, and ‘feeling jumpy, get a fright easily’, when they thought about any event which they had found traumatic. If participants showed signs of hypervigilance, intrusion, or avoidance then they were considered to have some PTSD symptoms. Scores were summed and the overall Cronbach alpha was 0.90.

The Childhood Trauma Questionnaire [50] measures 4 dimensions of use: neglect, emotional, physical and sexual abuse. Items for these dimensions were scored separately and if participants had any sign of use from at least one of the dimensions, it indicated some childhood trauma. The overall Cronbach alpha for the summed scores was 0.78.

Exposure to violence was assessed using the WHO violence questionnaire (adapted for female sex workers) [51].

Physical abuse by intimate partner or non-intimate partner (client, police, family and other men) was assessed using the following items: “Within the past year did any partner slap you, push you or throw something at you which could hurt you?”, “Within the past year did any partner hit you with a fist or with something else (such as a beer bottle, stick or belt) which could hurt you?”, “Within the past year did any partner kick, drag, beat, choke or burn you?”, and “Within the past year did any partner threaten to use or actually use a gun, knife or other weapon against you?”. Two variables were created using these items (physical abuse by intimate partner and physical abuse by non-intimate partner) with responses being categorised into none vs. some if participants had experienced any of the use from the items.

Sexual abuse by intimate partner or non-intimate partner (client, police, family and other men) was determined using the following items: “Within the past year did you have sex (vaginal/anal/oral) with any partner when you did not want to because you were afraid of what he might do?”, “Within the past year did any partner physically force you to have sex (vaginal/anal/oral) when you did not want to?” and “How many times has this (forced/fear sex/ rape) happened to you in the past 12 months?”. Two variables were created using these sexual abuse items (sexual abuse by intimate partner and sexual abuse by non-intimate partner) with responses none vs. some (per above). Furthermore, we created any physical or sexual abuse by an intimate partner and similarly any by a non-intimate partner.

The AUDIT-C scale [5] was adapted and used to indicate severe binge drinking. In addition to the 3 AUDIT questions: “How often do you have a drink containing alcohol?”, “How many drinks containing alcohol do you have on a typical day when you are drinking?”, and “How often do you have six or more drinks on one occasion?”, a question was included on the volume of alcohol per drink (mL). The four items were summed into a score, with a cut-off of 10 used to indicate binge drinking. The Cronbach alpha for the scale was 0.85.

Drug use was measured by asking participants the following questions, “How often have you taken: marijuana (dagga), mandrax, nyaope, cough mixture, ecstasy, methamphetamine (tik), painkillers and rock within the last year?”. Cocaine and heroin use were not consistently asked across both studies and therefore were excluded in the model but were included in the descriptive analysis. Responses were coded as “0 never”, “1 once”, “2 sometimes” and “3 often”. Participants scoring ≥1 for any substance question were considered to have used drugs.

Statistical analysis

Data from both sites were merged, thus the analyses excluded RDS weights and was analysed as a convenience sample. Frequencies and percentages for categorical variables were determined overall, and stratified by site (Soweto and Klerksdorp), by binge drinking, and by drug use. Median and interquartile ranges (IQR) were determined for continuous variables. Chi-square or Fisher’s exact tests were used to measure associations between categorical variables whereas the Kruskal-Wallis test was used for continuous variables stratified by binge drinking.

Since drug use data were collected at different times (past year in Soweto and past month in Klerksdorp), data were weighted for analysis on drug use to adjust for bias. Inverse probability weighting (IPW) using propensity scores (ps) was determined. Covariates included in calculating propensity scores were alcohol use, regular clients and age at sex debut. IPW was calculated by the formula if they used drugs and if they did not use drugs [52].

Thereafter, three separate weighted Poisson regression models (overall and by site) were used to evaluate risk factors associated with drug use at both univariate and multivariate level. However, risk factors associated with binge drinking were assessed using unweighted Poisson regression modelling as data was collected at the same time points. All variables were included in the full multivariate model and backward selection method used to select variables for inclusion in the final multivariate models.

Statistical analysis was performed using SAS Enterprise Guide 7.1 (SAS Institute, Cary, NC) and statistical significance was set at p-value ≤ 0.05.

Ethics approval

Ethical approval for both studies was provided by the Human Research Ethics Committee (Medical) of the University of the Witwatersrand, South Africa.

Results

Participant characteristics by site

Table 1 details participant characteristics by site; including socio-demographics, HIV status and treatment, mental health, experienced trauma, and substance use.

Table 1

Participant characteristics by site.

Variable	Overall (n = 664)	Soweto (n = 508)	Klerksdorp (n = 156)	P-Value
Median Age (IQR)	30.0 (25.0–36)	30.0 (25.0–36)	32.0 (25.0–36)	0.2887
Immigration status
Local (%)	453/664 (68.22)	346/508 (68.11)	107/156 (68.59)	0.9915
Internal Immigrant (%)	190/664 (28.61)	146/508 (28.74)	44/156 (28.21)
External Immigrant (%)	21/664 (3.16)	16/508 (3.15)	5/156 (3.21)
Level of education
No schooling/primary only (%)	57/664 (8.58)	37/508 (7.28)	20/156 (12.82)	0.0308
Incomplete high school (%)	450/664 (67.77)	347/508 (68.31)	103/156 (66.03)	0.5938
High/ post school qualification (%)	157/664 (23.64)	124/508 (24.41)	33/156 (21.15)	0.4026
Do the people in your home regularly go without food?
Yes (%)	466/664 (70.18)	326/508 (64.17)	140/156 (89.74)	< .0001
How old were you when you first had sex?
Median (IQR)	17.0 (15.0–18)	17.0 (15.0–18)	16.5 (15.0–18)	0.6007
Under what circumstances did you first have sex?
Coercive (%)	123/664 (18.52)	110/508 (21.65)	13/156 (8.33)	0.0002
How old were you when you first sold sex?
Median (IQR)	24.0 (20.0–30)	25.0 (20.0–30)	23.0 (20.0–30)	0.5847
HIV Status
Positive (%)	361/664 (54.37)	280/508 (55.12)	81/156 (51.92)	0.4834
Self-reported HIV
Known Positive	300/351 (85.47)	227/271 (83.76)	73/80 (91.25)	0.0950
Newly diagnosed	51/351 (14.53)	44/271 (16.24)	7/80 (8.75)
Are you on treatment?
Never taken treatment (%)	94/300 (31.33)	90/229 (39.30)	4/71 (5.63)	< .0001
On treatment always (%)	190/300 (63.33)	130/229 (56.77)	60/71 (84.51)	< .0001
Stopped taking treatment (%)	16/300 (5.33)	9/229 (3.93)	7/71 (9.86)	0.0521
Self-reported adherence
Non-adherence (%)	8/190 (4.21)	4/130 (3.08)	4/60 (6.67)	0.2521
Adherence (%)	182/190 (95.79)	126/130 (96.92)	56/60 (93.33)
Depression
Depressive symptoms (%)	460/664 (69.28)	348/508 (68.50)	112/156 (71.79)	0.4358
PTSD
PTSD symptoms (%)	212/664 (31.93)	195/508 (38.39)	17/156 (10.90)	< .0001
Childhood trauma
Some childhood trauma (%)	590/664 (88.86)	493/508 (97.05)	97/156 (62.18)	< .0001
Physical/sexual abuse from IP within the past year
Some abuse (%)	349/664 (52.56)	288/508 (56.69)	61/156 (39.10)	0.0001
Physical/sexual abuse from non-IP within the past year
Some abuse (%)	344/664 (51.81)	276/508 (54.33)	68/156 (43.59)	0.0189
Binge drinking
Non-binge drinkers (%)	291/664 (43.83)	230/508 (45.28)	61/156 (39.10)	0.1741
Binge drinkers (%)	373/664 (56.17)	278/508 (54.72)	95/156 (60.90)
Within the last year, did you use any drugs?
No (%)	469/664 (70.63)	344/508 (67.72)	125/156 (80.13)	0.0029
Yes (%)	195/664 (29.37)	164/508 (32.28)	31/156 (19.87)
Substance use
Binge drinking and drug use (%)	83/664 (12.50)	59/508 (11.61)	24/156 (15.38)	0.2129
Binge drinking or drug use (%)	402/664 (60.54)	324/508 (63.78)	78/156 (50.00)	0.0021
None (%)	179/664 (26.96)	125/508 (24.61)	54/156 (34.62)	0.0137

There were a total of 664 FSW participants, of whom, 76.51% (508/664) were enrolled in Soweto and 23.49% (156/664) in Klerksdorp. Across both sites, the median age was 30 years (IQR: 25–36); and 68.2% (453/664) were local residents. Compared to Klerksdorp, Sowetan participants were less likely to have no or primary level education only (7.2% vs. 12.8%; p = 0.0308) and to regularly go without food in their household (64.2% vs 89.7%; p<0.0001).

Respondents’ median age at sexual debut was 17 years (IQR: 15–18) and 18.5% (123/664) reported their first sexual encounter as coercive. Participants from Soweto were almost three-fold more likely to be coerced into having sex for the first time (21.7% vs. 8.3%; p = 0.0002) than those from Klerksdorp. The median age of first selling sex across both sites was 24 (IQR: 20–30) years.

HIV prevalence at both sites was similar; 55.1% (280/508) in Soweto and 51.9% (81/156) in Klerksdorp (p = 0.4834). Across both sites, of those who tested positive for HIV, 14.5% (51/351) were newly diagnosed. Of the known positives (85.5%, n = 300/351), 63.3% (190/300) self-reported always being on ART, with a higher proportion of participants receiving ART in Klerksdorp compared to Soweto (84.5% vs. 56.8% respectively; p<0.0001). Of the 190 participants always on ART, across both sites, 95.8% (n = 182) self-reported adherence.

Overall, 69.3% (460/664) and 31.9% (212/664) of participants showed symptoms of depression and PTSD, respectively. About 88.9% (590/664) reported childhood trauma. Though not significant, a slightly higher proportion of FSW in Klerksdorp had depressive symptoms compared to Soweto (71.8% vs. 68.5%; p = 0.4358). Compared to Klerksdorp participants, FSWs from Soweto were fourfold more likely to report PTSD symptoms (38.4% vs. 10.9%; p<0.0001), experienced higher levels of childhood trauma (97.1% vs. 62.2%; p<0.0001), and experienced both physical/sexual abuse by both IPs and non-IPs in the past year (56.7% vs. 39.1%; p = 0.0001; and 54.3% vs. 43.6%; p = 0.0189, respectively).

Of the 664 FSW, 56.2% (373/664) were classified as binge drinkers and 29.4% (195/664) self-reported drug use within the past year (dagga [58.9%, 115/195], mandrax [3.08%, 6/195], nyaope [2.56%, 5/195], cough mixture [29.7%, 58/195], painkillers [27.7%, 54/195], ecstasy [10.3%, 20/195], Tik [4.62%, 9/195] and rock [2.56%, 5/195]). While not significant, a higher percentage of participants from Klerksdorp reported binge drinking compared to Soweto (60.9%, vs 54.7%; p = 0.1741), while significantly more participants from Soweto reported last year drug use (32.3% vs 19.9%; p = 0029). Overall, 12.5% (83/664) of participants reported both binge drinking and drug use with no significant difference by site.

Participant characteristics by substance use

Table 2 depicts participant characteristics by binge drinking and drug use.

Table 2

Participants characteristics by binge drinking and drug use.

Variable	Overall	Binge Drinkers	Non-binge Drinkers	P-Value	Some Drug Use	No Drug Use	P-Value
No. enrolled	664 (100.00)	373 (56.17)	291 (43.83)	-	195 (29.37)	469 (70.63)	-
Site
Klerksdorp (%)	156/664 (23.49)	95/373 (25.47)	61/291 (20.96)	0.1741	31/195 (15.90)	125/469 (26.65)	0.0001
Soweto (%)	508/664 (76.51)	278/373 (74.53)	230/291 (79.04)		164/195 (84.10)	344/469 (73.35)
Median Age (IQR)	30.0 (25.0–36)	30.0 (25.0–36)	31.0 (25.0–36)	0.3901	31.0 (24.0–36)	30.0 (25.0–36)	0.3159
Do the people in your home regularly go without food?
Yes (%)	466/664 (70.18)	248/373 (66.49)	218/291 (74.91)	0.0185	138/195 (70.77)	328/469 (69.94)	0.6110
How old were you when you first sold sex?
Median (IQR)	24.0 (20.0–30)	24.0 (20.0–30)	25.0 (20.0–30)	0.9016	24.0 (19.0–29)	25.0 (20.0–30)	0.2100
HIV Status
Positive (%)	361/664 (54.37)	214/373 (57.37)	147/291 (50.52)	0.0784	98/195 (50.26)	263/469 (56.08)	0.3420
How old were you when you first had sex?
Median (IQR)	17.0 (15.0–18)	16.0 (15.0–18)	17.0 (15.0–18)	0.2503	17.0 (15.0–18)	17.0 (15.0–18)	0.9999
Under what circumstances did you first have sex?
Coercive (%)	123/664 (18.52)	69/373 (18.50)	54/291 (18.56)	0.9848	44/195 (22.56)	79/469 (16.84)	0.0038
Depression
Depressive symptoms (%)	460/664 (69.28)	261/373 (69.97)	199/291 (68.38)	0.6598	135/195 (69.23)	325/469 (69.30)	0.6675
PTSD
PTSD symptoms (%)	212/664 (31.93)	110/373 (29.49)	102/291 (35.05)	0.1272	85/195 (43.59)	127/469 (27.08)	< .0001
Childhood trauma
Some childhood trauma (%)	590/664 (88.86)	332/373 (89.01)	258/291 (88.66)	0.8875	180/195 (92.31)	410/469 (87.42)	0.0217
Physical/sexual abuse from IP within the past year
Some abuse (%)	349/664 (52.56)	201/373 (53.89)	148/291 (50.86)	0.4381	131/195 (67.18)	218/469 (46.48)	< .0001
Physical/sexual abuse from non-IP within the past year
Some abuse (%)	344/664 (51.81)	174/373 (46.65)	170/291 (58.42)	0.0026	133/195 (68.21)	211/469 (44.99)	< .0001
Binge drinking
Binge drinkers (%)	373/664 (56.17)	-	-		83/195 (42.56)	290/469 (61.83)	0.8921
Within the last year, did you use any drugs?
Yes (%)	195/664 (29.37)	83/373 (22.25)	112/291 (38.49)	0.8921	-	-

Non-binge drinkers were more likely to have regularly gone without food (74.9% vs. 66.5%; p = 0.0185), and to have experienced physical/sexual abuse from non-IP within the past year (58.4% vs. 46.7%; p = 0.0026).

FSWs who used drugs were more likely to be from Soweto (84.1% vs. 73.4%; p = 0.0001), to have been coerced at first sex (22.6% vs. 16.9%, p = 0.0038), to have PTSD symptoms (43.6% vs. 27.1%; p<0.0001), to have experienced some childhood trauma (92.3% vs. 87.4%, p = 0.0217) and have experienced physically/sexually abuse from their IPs and non-IPs within the past year (67.2% vs. 46.5%, p<0.0001; and 68.2% vs. 45.8%, p<0.0001) compared to those who reported no drug use.

Risk factors associated with substance use

Overall risk factors

Table 3 reports the overall risk factors associated with substance use.

Table 3

Factors associated with binge drinking and drug use among female sex workers.

	Binge drinking				Drug use
	Univariate		Multivariate		Univariate		Multivariate
Variables	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value
Site
Soweto	Ref	-	Ref	-	1.3146 (1.0781–1.6030)	0.0069	1.1252 (0.8888–1.4246)	0.3269
Klerksdorp	1.1128 (0.9592–1.2910)	0.1585	1.1957 (1.0277–1.3912)	0.0207	Ref	-	Ref	-
Age (in years)	0.9956 (0.9870–1.0042)	0.3149	0.9815 (0.9675–0.9956)	0.0105	1.0064 (0.9966–1.0163)	0.2039	1.0030 (0.9929–1.0131)	0.5632
Immigration status
Local	Ref	-	Ref	-	Ref	-	Ref	-
External immigrants	0.9956 (0.6817–1.4541)	0.9818	-	-	0.7769 (0.4688–1.2876)	0.3274	0.7980 (0.4813–1.3230)	0.3817
Internal immigrants	0.9262 (0.7930–1.0818)	0.3330	-	-	0.8640 (0.7229–1.0327)	0.1082	0.8822 (0.7365–1.0567)	0.1735
Level of education
No/primary only	1.1805 (0.8986–1.5507)	0.2333	1.3252 (1.0057–1.7461)	0.0454	1.1630 (0.8751–1.5457)	0.2981	-	-
Incomplete high school	1.1917 (0.9979–1.4231)	0.0528	1.1791 (0.9908–1.4032)	0.0635	0.9698 (0.8078–1.1642)	0.7420	-	-
Matric/post school qualification	Ref	-	Ref	-	Ref	-	Ref	-
Do the people in your home go regularly without food?
No	1.1863 (1.0351–1.3595)	0.0140	1.2597 (1.1009–1.4413)	0.0008	Ref	-	Ref	-
Yes	Ref	-	Ref	-	0.9700 (0.8220–1.1447)	0.7188	-	-
How old were you when you first had sex?	0.9939 (0.9737–1.0145)	0.5593	0.9848 (0.9643–1.0057)	0.1529	0.9926 (0.9681–1.0177)	0.5608	-	-
Circumstance of first sex
Non-coercive	Ref	-	Ref	-	Ref	-	Ref	-
Coercive	0.9983 (0.8396–1.1870)	0.9848	-	-	1.2084 (1.0088–1.4475)	0.0398	1.0984 (0.9134–1.3210)	0.3185
How old were you when you first sold sex?	1.0018 (0.9918–1.0118)	0.7283	1.0168 (1.0002–1.0336)	0.0472	0.9988 (0.9875–1.0102)	0.8379	-	-
HIV status
Negative	Ref	-	Ref	-	Ref	-	Ref	-
Positive	1.1297 (0.9850–1.2956)	0.0813	1.1678 (1.0227–1.3334)	0.0219	0.9490 (0.8148–1.1054)	0.5012	-	-
PTSD
No PTSD symptoms	Ref	-	Ref	-	Ref	-	Ref	-
PTSD symptoms	0.8917 (0.7665–1.0375)	0.1379	-	-	1.3217 (1.1311–1.5445)	0.0004	1.1803 (1.0025–1.3895)	0.0465
Childhood trauma
No childhood trauma	Ref	-	Ref	-	Ref	-	Ref	-
Some Childhood trauma	1.0156 (0.8180–1.2610)	0.8883	-	-	1.2528 (0.9553–1.6430)	0.1032	0.9491 (0.6913–1.3029)	0.7464
Physical/sexual abuse from IP within the past year
No abuse	Ref	-	Ref	-	Ref	-	Ref	-
Some abuse	1.0548 (0.9215–1.2073)	0.4392	-	-	1.5515 (1.3202–1.8232)	< .0001	1.3648 (1.1522–1.6167)	0.0003
Physical/sexual abuse from non-IP within the past year
No abuse	Ref	-	Ref	-	Ref	-	Ref	-
Some abuse	0.8134 (0.7107–0.9309)	0.0027	0.8002 (0.6993–0.9156)	0.0012	1.5369 (1.3096–1.8036)	< .0001	1.3910 (1.1793–1.6407)	< .0001

Being from Klerksdorp (RR: 1.1957, 95% CI: 1.0277–1.3912), living in a home with regular food provision (RR: 1.2597, 95% CI: 1.1009–1.4413; p = 0.0008), having no or only primary level education (RR: 1.3252, 95% CI: 1.0057–1.746; p = 0.0454) and being HIV positive (RR: 1.1678, 95% CI: 1.0227–1.3334; p = 0.0219) were associated with a higher risk for binge drinking. However, an increase in age per year (RR: 0.9815, 95% CI: 0.9675–0.9956; P = 0.0105), and physical/sexual abuse from non-IPs within the past year (RR: 0.8002, 95% CI: 0.6993–0.9156; P = 0.0012) were associated with lower risk of binge drinking.

Overall, having PTSD symptoms (RR: 1.1803, 95% CI: 1.0025–1.3895; p = 0.0465) and past year physical/sexual abuse from either IPs (RR: 1.3648, 95% CI: 1.1522–1.6167; p = 0.0003) or non-IPs (RR: 1.3910, 95% CI: 1.1793–1.6407; p<0.0001) were associated with higher risk of drug use.

Site-specific risk factors associated with substance use

Table 4 reports the risk factors for substance use by site.

Table 4

Factors associated with binge drinking and drug use among female sex workers in Soweto and Klerksdorp.

	Binge drinking				Drug use
	Univariate		Multivariate		Univariate		Multivariate
Variables	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value	RR 95% (CI)	P-Value
SOWETO
Age (in years)	1.0036 (0.9933–1.0140)	0.4948			1.0135 (1.0027–1.0245)	0.0145	1.0091 (0.9982–1.0200)	0.1013
Immigration status
Local	Ref	-	Ref	-	Ref	-	Ref	-
External immigrants	1.1689 (0.7898–1.7300)	0.4352	-	-	0.8912 (0.5370–1.4792)	0.6560	0.9471 (0.5701–1.5734)	0.8338
Internal immigrants	1.0632 (0.8951–1.2630)	0.4851	-	-	0.7796 (0.6351–0.9570)	0.0173	0.7888 (0.6420–0.9690)	0.0239
Do the people in your home go regularly without food?
No	1.2637 (1.0821–1.4759)	0.0031	1.2795 (1.1025–1.4849)	0.0012	Ref	-	Ref	-
Yes	Ref	-	Ref	-	1.0499 (0.8790–1.2540)	0.5914	-	-
How old were you when you first had sex?	0.9973 (0.9723–1.0230)	0.8376	-	-	1.0030 (0.9755–1.0313)	0.8323	-	-
HIV status
Negative	Ref	-	Ref	-	Ref	-	Ref	-
Positive	1.1714 (0.9953–1.3787)	0.0570	1.2030 (1.0290–1.4065)	0.0204	0.9129 (0.7715–1.0803)	0.2887	-	-
PTSD
No PTSD symptoms	Ref	-	Ref	-	Ref	-	Ref	-
PTSD symptoms	0.8878 (0.7503–1.0504)	0.1653	-	-	1.2589 (1.0630–1.4909)	0.0076	1.1572 (0.9739–1.3750)	0.0970
Childhood trauma
No childhood trauma	Ref	-	Ref	-	Ref	-	Ref	-
Some Childhood trauma	1.3793 (0.7384–2.5766)	0.3131	-	-	1.8071 (0.8578–3.8071)	0.1196	1.4149 (0.6654–3.0084)	0.3672
Physical/sexual abuse from IP within the past year
No abuse	Ref	-	Ref	-	Ref	-	Ref	-
Some abuse	0.9350 (0.7982–1.0953)	0.4052	-	-	1.6427 (1.3621–1.9811)	< .0001	1.4563 (1.1997–1.7678)	0.0001
Physical/sexual abuse from non-IP within the past year
No abuse	Ref	-	Ref	-	Ref	-	Ref	-
Some abuse	0.8051 (0.6877–0.9424)	0.0070	0.7843 (0.6739–0.9128)	0.0017	1.6267 (1.3557–1.9519)	< .0001	1.4606 (1.2115–1.7611)	< .0001
KLERKSDORP
Age (in years)	0.9751 (0.9593–0.9912)	0.0026	0.9853 (0.9688–1.0021)	0.0862	0.9720 (0.9481–0.9964)	0.0249	0.9733 (0.9494–0.9977)	0.0324
Immigration status
Local	Ref	-	Ref	-	-	-	-	-
External immigrants	0.5707 (0.1937–1.6815)	0.3090	0.6615 (0.2247–1.9472)	0.4531	-	-	-	-
Internal immigrants	0.5836 (0.4007–0.8501)	0.0050	0.8101 (0.5211–1.2592)	0.3493	-	-	-	-
Level of education
How old were you when you first had sex?	0.9863 (0.9565–1.0170)	0.3776	-	-	0.9508 (0.8999–1.0044)	0.0716	0.9533 (0.9004–1.0094)	0.1009
Physical/sexual abuse from IP within the past year
No abuse	Ref	-	Ref	-
Some abuse	1.5905 (1.2492–2.0251)	0.0002	1.4298 (1.1232–1.8201)	0.0037	1.0985 (0.7630–1.5816)	0.6133	-	-

Soweto-specific risk factors associated with binge drinking and drug use

In Soweto, FSWs living in a home with regular food provision (RR: 1.2795, 95% CI: 1.1025–1.4859; p = 0.0012) and being HIV positive (RR: 1.2030, 95% CI: 1.0290–1.4065; p = 0.0204) had an increased risk of binge drinking, whereas those who had experienced physical/sexual abuse from non-IP within the past year (RR: 0.7843, 95% CI: 0.6739–0.9128; p = 0.0017) had a lower risk of binge drinking.

Higher risk of drug use was associated with past year of physical/sexual abuse from both IPs (RR: 1.4563, 95% CI: 1.1997–1.7678; p = 0.0001) and non-IPs (RR: 1.4606, 95% CI: 1.2115–1.7611; p<0.0001). Being an internal immigrant was associated with lower risk of drug use (RR: 0.7888, 95% CI: 0.6420–0.9690; p = 0.0239).

Klerksdorp-specific risk factors associated with binge drinking and drug use

In Klerksdorp, physical/sexual abuse from an IP within the past year was associated with an increased risk of binge drinking (RR: 1.4298, 95% CI: 1.1232–1.8201; p = 0.0037), while an increase in age was associated with lower risk of drug use (RR: 0.9733, 95% CI: 0.9494–0.9977; p = 0.0324).

Discussion

Our analysis of 664 FSWs in two provinces of South Africa shows a high prevalence of substance use, with over half of the participants meeting criteria for binge drinking and more than a quarter engaging in drug use. Overall, living in a home with regular food and being HIV positive were associated with a higher risk of binge drinking. Having symptoms suggestive of PTSD and past year physical/sexual abuse from either IPs or non-IPs were associated with a higher risk of drug use.

Substance use is a growing public health concern, especially given the increasing rates of drug use in South Africa [17, 53]. As a key vulnerable population already underutilizing public health services, FSWs are at an added disadvantage. The prevalence of binge drinking (56.2%) reported in amongst FSWs in our studies is almost tenfold that of women in South Africa (6.4%) [54]. The overall prevalence of drug use in the past year (29.4%) is within the range given for FSWs in various South African cities (24.5–39.8%), even though it is an underestimate given the exclusion of cocaine and heroin [6]. Furthermore, our findings demonstrate that the risk factors for alcohol and drug use differ per site, thus highlighting the need for site-specific nuances to targeted interventions serving FSWs. This is the first study to describe FSWs in Klerksdorp, making these findings even more pertinent to an area with a high HIV burden [40] and with limited educational and employment opportunities for women [55, 56].

Drug use was significantly higher in Soweto compared to Klerksdorp. This could be a result of geographic scope and contextual factors, with Soweto being a larger area within a more urban setting and thus possibly having better access to drugs [25]. Critically, our study shows an inverse relationship between drug use and binge drinking across both sites, which could suggest that under certain social circumstances, FSWs may choose between alcohol or drugs, rather than both. It is concerning that South Africa has such a paucity in treatment facilities for substance use [57], with limited vertical programmes for FSWs to access support while continuing to earn a living. There is an urgent need to create integrated substance use programmes that support FSWs in ways appropriate to their needs and contextual dynamics.

Our results demonstrate a significant burden of self-reported mental health issues. Almost three-quarters of FSW reported suffering from symptoms of major depression. This is almost seven times higher than in the general South African population [16]. Compared to Klerksdorp, Soweto showed a higher proportion of PTSD symptoms, which is associated with high rates of childhood trauma and physical/sexual violence [58]. Our study shows that PTSD symptoms are associated with a higher risk of drug use. These findings may explain the higher prevalence of drug use in Soweto. Interestingly, our analysis of depression did not present as a strong risk factor for substance use, even though previous research has shown substance use to be a key risk factor for mental health problems among FSWs in low- and middle-income countries (LMICs) [59].

The findings of our study corroborate previous work showing the high prevalence of sexual and/or physical violence exposure amongst FSWs [6, 25]. This is of particular importance in Klerksdorp, where there is no previous research describing violence exposure for FSWs. In comparison to Soweto, Klerksdorp FSWs experienced less childhood trauma and were less likely to describe their first sexual experience as coercive. They were also significantly less likely to report exposure to past year physical and/or sexual violence–a major risk factor for substance use, which our study also reports [6]. It is unsurprising then that we find lower levels of substance use (both alcohol and drug use) in Klerksdorp, where violence exposure was lower. Meanwhile, variables such as food security and a positive HIV status increased the risk of binge drinking. This is in contrast to literature that suggests that one of the most common structural drivers of substance use in occupational groups at high risk of HIV in South Africa is widespread poverty [60]. Food insecurity and substance use have been shown to be highly correlated for men but not women [61]. The latter variable is unsurprising given the demonstrated association between substance use and medication non-adherence, and the explanation that substance use can serve as a coping mechanism for dealing with a chronic illness [62]. The risk factor of a positive HIV status for binge drinking is notable because heavy drinking can lead to high-risk sexual behaviours, increased potential for HIV transmission, sub-optimal ART adherence, and other health complications including liver disease [63].

Our study had several limitations. The smaller sample size in Klerksdorp likely impacts the precision of the findings. The data was collected at differing time periods at each site, and changes in context could account for differences in findings. This is of particular importance for ART uptake, which due to a policy change in late 2016, improved access for HIV positive FSW. Self-reported ART-use could also have been impacted by social desirability bias. The AUDIT-C short measure is possibly inadequate to assess chronic binge drinking. Drug use was measured differently across the two sites: Klerksdorp asked about drug use in the past month and Soweto asked about drug use in the past year. As such the variable explored drug use “within the last year”. Cocaine and heroin use was not measured in Soweto and therefore was excluded from the model. Additionally, we do not have longitudinal data on substance use.

Conclusions and recommendations

Our research shows the high prevalence of substance use by FSWs in two locations in South Africa, which suggests either the lack of awareness of or access to effective interventions. Urgent interventions are required to address this concern. The high rates of physical and sexual abuse throughout the lives of FSW and ill mental health is noteworthy, given the known links between/among trauma, ill mental health and substance use. Interventions for physical and sexual abuse are required not only at the individual-level, but also the community-level to include male intimate partners and non-intimate partners who perpetrate violence, and structural-level to address legislative frameworks which drive vulnerability amongst FSWs while allowing male partners to act with impunity. Given the trauma exposure of this population, it is unsurprising that such high rates of substance use are found. Interventions targeted at drivers of mental illness are needed, as well as those geared towards specifically supporting women suffering from mental illness.

There is a current paucity of knowledge on substance use and sex worker dynamics, which will likely hinder efforts to develop effective long-term substance use, mental health, and gender-based violence-related interventions. Our findings highlight site-specific contextual dynamics driving substance use and can be used to better tailor interventions for FSWs in South Africa, where contextual dynamics vary widely across the country. Broader research is needed to better understand the site-specific risk factors for alcohol and/or drug use in populations with an increased risk of substance use due to occupation-related factors.

Klerksdorp version of complete study questionnaire.

(PDF)

Click here for additional data file.

Questionnaire tools.

(PDF)

Click here for additional data file.

31 Aug 2021

PONE-D-21-22797

Key Risk Factors for Substance Use among Female Sex Workers in Soweto and Klerksdorp, South Africa: A cross-sectional study

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Reviewer #1: Thank you for opportunity to review. Apologies for brevity. Your reviewer is unwell with Covid but I wanted to get this back so the authors could address speedily.

The subject matter explored is highly relevant and speaks to understanding and meeting the needs of a key generally marginalised population. Congrats!

The literature review is appropriate. There are however a few brief points of reflection.

In the abstract:

1. At line 37: Include a note about which survey? was it developed for this study? Evaluating what exactly? Validated?

2. At line 40, with reference to the text “key risk factors of alcohol and drug use” it might assist if this was clearer on whether this referred to Risks for or risks resulting from or all risks?

In the introduction

3. At lines 58 and 59, the authors might perhaps consider using more current references. For line 58 The authors need to cite more current publications such as the most recent World Drug Report, which will have been published in the period since this manuscript was probably submitted.

4. Line 60 refers to a diagnosis of drug use. Were the authors intending to refer to a diagnosis of substance use disorder? Can drug use be “diagnosed”?

5. The final sentence of the first paragraph at lines 62 and 63, This statement is not supported by the provided stats. The sentence should perhaps read "...vary widely and this is likely a consequence of cultural and other environment factors" This statement would itself need a reference.

6. At line 86, Should there be centres specifically dedicated to FSW? Would this not further marginalize and stigmatize this population?

7. At line 87, the text “access to the few treatment centres is limited” refers. In what way is access limited? Some brief reflection on this might assist.

8. At line 89, there is reference to competing financial priority while in treatment. In what way? Could the authors provide a brief text for clarity in the manuscript.

9. At line 112 there is an appropriate refence to relationship to viral suppression consequent upon poor adherence. The links need to be stated more explicitly here and in terms of reduces access to health care in the next sentence, to clearly set the scene.

10. At line 117, The correct note about substance use being currently infrequently studied, as well needs to be more explicit. What about the substance use is infrequently studied? Is it substance use patterns? Is it substance use in general. I know what the authors are referring to but the writing needs to be more explicit for any reader.

In the Methods Section

11. At line 123, Is this manuscript reporting on two studies, or is it reporting on the findings of data collected at two sites at different times? Do these studies have separate Ethical clearance or is the newer sample an extension of the original approval?

12. At line 124, Brief description to link to the next sentence, RDS methodology, where an initial group of respondents assembled via convenience sampling are asked to invite additional participants from within their network" or something along those lines...

13. At line 133, the statement indicating the population size of Soweto needs a reference.

14. At line 144: As I am familiar with the implementing partner landscape in South Africa, I know what this means, but a reader from elsewhere might not be clear. This sentence should more explicitly clarify what these programmes are, what they do so as to clearly link the reader to why it is that they would have access to and the trust of FSW's

15. At line 157, Per above , perhaps some brief context into what the sex worker programme is.

16. At line 168 regarding data collection, what is meant by privately and collaboratively? Could this be made clearer in the text of the article?

17. In general the data collection process is not clear. The authors should seek to describe this in a way that is easy to follow and replicate.

18. At line 174 the authors refer to RDS assumptions and how these were managed. Which assumptions specifically?

19. At line 181 the following text refers “A detailed description of all measures used has been included in other papers” Please still at least list the measures or at least mention they are detailed below. (Having subsequently read further) Seeing as they are detailed below I'm not sure this sentence is essential)

20. At line 185, could the authors please clarify “cognitive interviews”? This can be confusing, particularly for this population as this is so often used in reference to law enforcement procedures.

21. The authors refer to physical and sexual use by partner throughout the manuscript. Is this correct or is it meant to refer to “abuse”. If “use is correct, please define?

22. My initial feeling was that the tables were possibly cumbersome, but they are in fact very handy, and I hope they can be retained in the final publication.

The authors have done an excellent job of characterising this population at these sites and eliciting their risk profiles for harmful substance use.

This material is not only suitable fir publication but will add great value in the consideration of responsive service provision for this key population. It should certainly be considered for publication with these minor revisions.

Authors have largely adhered to the STROBE recommendations, which apply to this type of study. They should refer more explicitly to the ways in which they have done so, and this might assist in addressing some minor gaps. For example, with this population is is especially important to consider ethical issues and speak to how potential bias has been addressed.

Per my input above, the procedures of the study could be described somewhat more explicitly so as to assist with replicability.

The manuscript is well organized but some clarifications and suggested above might assist in making the material more accessible to a broader readership.

This manuscript in my view does not contain an NIH-defined experiment of Dual Use Concern

Reviewer #2: Overall, really interesting paper with really interesting findings. There is just one piece that concerns me is drug use in the past month for Klerksdorp population and drug use in the past year for the Soweto population. See my last comment for suggestions on how to address this. All other comments are minor revisions.

Line 116-117 The intro section is full of strong statistics about SU in FSW populations. It is a bit of a contradiction to say something has been infrequently studied, when you have presented several articles to support SU in FSW populations (Line 65-68, 70, 72,77). The sentence should read “despite the high prevalence of trauma and mental health, gaps exist when focusing on binge drinking and drug use (although I do think you provided evidence that there is no gap when focused on drug use). The focus of this study is to describe the prevalence of self-reported binge drinking, and associated risk factors” or something similar. I think just a simple reivision will address this

Line 124 “enroll” Small spelling error

Line 126-127 “The full methodology from the Soweto study has been extensively described previously (7)” Language could be a better. For example: “The methods from the Soweto study has been throughly described in previous publications (7)”

Keep language consistent. Sometimes you utilize “FSW” and sometimes “woman.” For consistency, choose one! (End of line 136).

Line 137 “informal sex work was also paid for in beer” Do you have a citation for this?

Line 168 “Post enrollment” Another small spelling error.

Line 411-413 This is interesting and could also be a focus of future research. In what circumstances are FSW using both?

Line 450-452 The focus on HIV and ART feels a little out of place. I understand the big picture relationship, but how does this relate to the objective of the analysis which was to determine the prevalence and associated risks of binge drinking and drug use? 
Other limitations: cross sectional design.

Line 455: Because the Kleksdorp population was only asked about past month drug use, was this adjusted to reflect what the past year use would be? This assumes that every month has similar patterns of drug use, which I think is a feasible assumption. This could also explain why drug use was higher in Soweto compared to Kerksdorp. I think this is a glaring problem that needs to be adjudicated in either the methods to explain how you adjusted for this discrepancy or in the results, where you use the one month report to predict one years use, using the assumption the the report of one month's use is reflective of use in all the other months. This may change your results.

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Reviewer #1: No

Reviewer #2: No

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Submitted filename: Comments.docx

Click here for additional data file.

16 Nov 2021

To address the additional requirements noted in the Decision Letter:

1. Manuscript has been edited to meet PLOS ONE's style requirements.

2. The questionnaire used for the Soweto and Klerksdorp study was developed by merging existing and validated tools such as: 10-item CES-D short scale for depression, PTSD-8 scale, The AUDIT-C scale for alcohol use, The Childhood Trauma Questionnaire and the WHO violence against women (adapted for female sex workers). All of these questionnaires have been referenced in the manuscript.

3. We have not uploaded the data onto a data repository and now included the below sentences under the Data Availability Statement: Female sex workers are a highly vulnerable key population due to violence, stigma and the criminalised nature of the work. For this reason it is imperative that data collected from studies with female sex workers follow ethical considerations and account for the sensitive nature of the information. Therefore, datasets will be available upon request by contacting info@phru.co.za.

Please see the "Response to Reviewers" document for responses that correspond to reviewer comments. (Responses have been copied below but will be better understood when viewing the comments side by side in the document)

Dear Reviewer thank you for your comment. Please find our specific responses below.

Thank you for your comment. A note has been included in the abstract highlighting that the survey was developed for the study and the information collected included socio-demographic, mental-ill health, violence and HIV status.

This sentence has been revised to “risk factors for alcohol and drug use.”

The reference has been updated to a more recent 2018 WHO report.

The sentence has been revised to “diagnosis of substance use disorder.”

The sentence has been revised. The statement uses the same reference as the preceding sentence.

This is an important point. Through our work with FSWs we have learnt that by having a dedicated sex workers only space, that provides targeted health services in a safe and trusting environment, we are able to increase the uptake of health services and treatment adherence while simultaneously providing psycho-social support. However, it is important to ensure that dedicated spaces are run by personnel who have been sensitized to working with key populations to mitigate stigmatization and marginalization. Due to the nature of sex work, FSW risk being marginalized and stigmatized when accessing services from general facilities and substance use could potentially add to this stigma. We therefore, believe that there should be centres specifically dedicated to FSW because they face unique challenges and risk factors and experience a high prevalence of substance use disorder. We believe that the benefits of a FSW only centre would minimize the risk of stigmatization and create a space where FSWs can seek treatment specific to their needs.

Thank you for your comment. This statement has been clarified such that access is limited by limited availability of space and services.

The “competing financial priority” refers to the fact that FSW cannot work and earn an income while they are in treatment. The sentence has been revised for clarification.

Thank you for your comment. The statement has been amended for clarity and the sentence referring to ‘access to healthcare’ has been moved to paragraph three.

The sentence has been revised to “patterns of substance use.”

This manuscript is reporting on findings of data collected from two studies. The studies were conducted at different sites but followed the same methodology. The two studies have separate ethical clearance certificates. This has been made clearer in the manuscript.

The phrase has been adapted to provide a stronger link to the next sentence.

A reference to the 2011 census has been added.

More information about the sex worker programmes have been added.

More information about the sex worker programmes have been added.

Thank you for the comment, the sentence has been revised for clarity.

The data collection process has been amended for clarity and replicability.

The RDS assumptions made include: that the population being recruited must know one another as FSW, participants recruited have similar characteristics, must be networked and could accurately estimate their network size and peer to peer recruitment is random. A reference has been added in the manuscript that refers to the RDS assumptions.

Thank you for the comment, the sentence has been deleted.

Thank you for your comment, cognitive interviews were conducted to assess the understandability and appropriateness of the questionnaire. This has been described in the manuscript.

Thank you for the comment. This was an error and all instances of “physical/sexual use” has been corrected to “physical/sexual abuse.”

Thank you for the comment. We will keep the tables in the final publication.

Thank you for these final remarks, we have reviewed the STROBE recommendations and hope that in addressing the reviewers comments we have managed to fill any noted gaps especially around ethical issues and bias.

Dear reviewer, thank you for your comments. Please find our specific responses below.

We revised the sentence to incorporate both your and Reviewer 1’s feedback. The sentence now reads “Despite the high prevalence of trauma and mental health concerns reported by FSWs in South Africa, gaps exist when focusing on patterns of substance use for this population.”

The spelling error has been corrected.

The sentence has been revised to “the methodology from the Soweto study has been thoroughly described in previous publications.”

The end of line 136 has been switched to “FSW.”

This was an error. Citation 24 was moved to encompass the entire sentence which it refers to.

The spelling error has been corrected.

Thank you for your comment. While we do agree that understanding the circumstances for both binge drinking and drug use would be an interesting topic for future research our numbers were too small to compare for this manuscript especially as it would need to be split by site.

Thank you for your comment. As noted in the introduction, previous studies have found that substance use is linked to HIV and ART adherence. Additionally, HIV status has been associated with substance use with our analysis finding that Hiv status increased risk of binge drinking. As FSW have a higher HIV prevalence than the general population we believe it is important to include HIV and ART when determining the patterns and risk factors for substance use amongst this population.

We have noted in the limitations section that we do not have longitudinal data on substance use.

Thank you to the reviewer for the comment. We decided to use Inverse Probability Weighting using propensity score to adjust for the time difference in both site. We have explained the process in the method section and updated the results to account for the adjustment done.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

13 Dec 2021

Key risk factors for substance use among female sex workers in Soweto and Klerksdorp, South Africa: A cross-sectional study

PONE-D-21-22797R1

Dear Dr. Yeo,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Yukiko Washio, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

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Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Initial comments have been sufficiently addressed and manuscript reads strongly and clear. A single additional minor recommendation might be where it is said that FSW'w were used to identify additional participants. Could the authors consider a word or phrase to say this more sensitively for what is a vulnerable population?

Reviewer #2: As I mentioned before, I really enjoyed reading this paper. Great job with the revisions. Best of luck!

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #1: No

Reviewer #2: No

11 Jan 2022

PONE-D-21-22797R1

Key risk factors for substance use among female sex workers in Soweto and Klerksdorp, South Africa: A cross-sectional study

Dear Dr. Yeo:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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PLOS ONE