Preventing sexually transmitted and blood borne infections (STBBIs) among sex workers: a critical review of the evidence on determinants and interventions in high-income countries

This review triangulates information and data obtained from searching peer-reviewed reports published in English in key databases: PubMed (MEDLINE), Social Sciences Citation Index, Science Citation Index Expanded, Arts & Humanities Citation Index, and Emerging Sources Citation Index (via Web of Science). The following search terms were used in combination and connected with “and”: sex work terms (“sex work*” OR “sex worker” OR “prostitut*” OR “prostitution” OR “commercial sex worker*” OR “transsexual” OR “cross dresser” OR “transvestite” OR “escort” OR “gay for pay”); HIV/STBBI-related terms (“HIV” OR “human immunodeficiency virus” OR “HIV infections” OR “AIDS” OR “acquired immunodeficiency syndrome” OR “acquired immune deficiency syndrome” OR “condom use” OR “non-condom use” OR “condom non-use” OR “unprotected sex” OR “condom refusal” OR “condom negotiation”, “condom utilization”, “sexually transmitted infection*”, “STI”, “blood borne infection*” OR “STBBI” OR “STD” OR “sexually transmitted disease*” OR “hepatitis C” OR “HCV” OR “chlamydia” OR “gonorrhea” OR “syphilis”); risk and intervention-related terms (“risk factor*” OR “correlate” OR “determinant” OR “predictor” OR “risk” OR “HIV risk” OR “risk behavior*” OR “risk behaviour*” OR “intervention*” OR “empowerment” OR “community-based” OR “treatment” OR “prevention” OR “strateg*” OR “structural approach*”); terms for high-income countries (“Canada” OR “United States” OR “USA” OR “US” OR “North America” OR “England” OR “United Kingdom” OR “UK” OR “Australia” OR “New Zealand” OR “Europe” OR “Spain” OR “Italy” OR “Germany” OR “France” OR “Finland” OR “Denmark” OR “Norway” OR “Sweden” OR “Austria” OR “Switzerland” OR “Belgium” OR “Portugal” OR “Netherlands” OR “Holland” OR “Japan” OR “Czech Republic” “Greece” OR “Hungary” OR “Iceland” OR “Ireland” OR “Korea” OR “Luxembourg” OR “Slovak Republic”). EA and SG did initial screening and EA extracted relevant data and information from each study (i.e., country, study design, population, STBBI and condom use outcomes, individual/interpersonal and structural determinants and interventions) and relevant reports.

The search was supplemented with additional sources, including publicly available reports (e.g., Open Society Foundation, NSWP, WHO and UN reports), and qualitative/ethnographic peer-reviewed research where quantitative evidence was limited.

We included quantitative studies that examined risk factors for STBBIs (e.g., HIV, HCV, chlamydia, gonorrhea or syphilis) or condom use (including condom refusal and unprotected sex) among cis female, cis male, and trans sex workers in high-income countries. Non-primary research (e.g., commentaries), studies without full-text sources available (e.g., abstracts), studies in which STBBIs or condom use were not analyzed as outcomes, studies that did not report multivariable analyses, and those that did not stratify results by sex workers were excluded. Qualitative studies and publicly available reports were included to provide further context around quantitative work. We excluded studies that focused solely on adolescents (< 18 years), studies from LMICs, and non-English publications.

To date, most research on sex work and STBBIs has focused on the experiences of female sex workers. Despite reports on the high prevalence of STBBIs among both cis men and trans sex workers [21‐24], little data exist on the determinants of STBBIs unique to these populations. Current evidence suggests the determinants of STBBIs for sex workers of any gender are highly multifaceted. Individual and interpersonal determinants (including substance use and sexual risk practices, mental health, and partner-level variables, among others) were examined in 12 studies focusing on female sex workers (Table 1), 3 studies focusing on cis male sex workers (Table 2), and 3 studies focusing on trans sex workers (Table 3).

While the HIV epidemic among sex workers is predominantly driven by sexual transmission [2, 7, 25], sex workers who inject drugs are at elevated risk for HIV/STBBIs through dual drug and sexual risk pathways. Among female sex workers in Europe, injecting drugs is the primary individual-level determinant of HIV [26]. A recent systematic review estimates 35–65% of female sex workers in the USA use injection drugs, and reported rates of crack use were as high as 75% [27]. In a recent study of 1647 people who inject drugs in Vancouver, sex workers who injected drugs had a significantly higher cumulative incidence of HIV than other injection drug users (12% vs. 7%); multivariable analyses suggest that HIV risk for sex workers who inject drugs appears to be modified by contextual factors and dual sexual and risks linked to daily cocaine injection [28].

Dual drug and sexual risk behaviours significantly enhance risks for STBBI transmission among sex workers and their partners. Studies of interpersonal determinants of STBBIs have begun to identify how types of partners (e.g., regular or one-time clients and intimate/non-paying partners) shape sexual risks and STBBI transmission dynamics. For example, condoms are less likely to be used in transactions with regular clients as compared to one-time clients, and similar to estimates in the general Canadian population, nearly three-quarters of female (trans inclusive) sex workers in Canada report recent inconsistent condom use with intimate partners [29]. Among indoor-working cis female sex workers in the UK, having an intimate partner was significantly associated with prevalence of HIV and other STBBIs [30].

In Canada, Indigenous sex workers (i.e., First Nations, Metis, Inuit ancestry) are more than twice as likely to be living with HIV than their non-Indigenous counterparts, and being younger, substance using, and reporting unprotected sex were all associated with increased risk of STBBIs [25, 31‐33]. A Los Angeles based study among cis female and trans women sex workers identified African/American ethnicity, higher income, cohabitation, and not seeking recent health care as predictors of lower HIV prevention utilization [34]. While the vast majority of sex workers initiate sex work in adulthood, duration of time in sex work has been shown to shape risk pathways for STBBIs, including increased risk for HIV infection among women sex workers in Vancouver and Miami [31, 35]. Among cis female sex workers in Korea, younger age and higher inconsistency of condom use were associated with chlamydia infection [36]. Male sex workers (MSWs) in Europe report injecting drugs significantly longer than other men who inject drugs, with a higher proportion sharing needles (23% vs. 14%), and MSWs reported incarceration at a significantly younger age than their non-sex worker counterparts [37]. In the Netherlands, younger men were more than twice as likely to test positive for STBBIs, and identifying as gay or bisexual significantly increased risk [22].

Despite dual drug and sexual risks, little is known about the burden of HCV among sex workers. One study found elevated risk for HIV-HCV co-infection among sex workers in Canada: close to half (44%) of sex workers in the study had HCV, with higher odds among women who reported having a recent STI, being HIV positive, Indigenous ancestry, engaging in sex work longer, older age, and working outdoors [38]. The HCV incidence density was 4.28 events/100 person-years, with highest rates among sex workers who inject drugs, and multivariable analysis demonstrated both STI and non-injection stimulant crack use to be major pathways to HCV infections [38]. HCV prevalence among cis female sex workers who do not inject drugs in Korea was positively associated with history of acupuncture and diabetes [39].

Globally, trans women sex workers can have up to six times increased odds of HIV infection than cis male or cis female sex workers, with injection drug use being highly prevalent among those living with HIV [40, 41]. Limited Canadian research highlights the wide range of sexual risks and heterogeneity of trans individuals; in Ontario, only half of trans women (of which 15% had a history of sex work) were ever tested for HIV [42].

Among MSWs, risks for STBBIs are driven by a range of unique biological and structural factors and this population has seen a sustained and possibly increasing burden of HIV/STBBI globally [1, 43]. The primary risks for STBBIs identified among MSWs include unprotected anal intercourse, having a high number of sexual partners and large sexual networks, and stigma [7, 44‐47]. Some evidence suggests that a higher proportion of MSWs report condom use than gay men or other men who have sex with men (MSM) who do not exchange sex: 51% vs. 30%, respectively [44]. In Ontario, MSWs were more likely to test positive for HIV and HCV-HIV co-infection than MSM not involved in the sex industry [48]. Among the limited available data among MSWs, research from the UK found that rates of both unprotected sex and gonorrhoea both increased steadily over the study period (1994–2003) [21]. Among MSWs in the Netherlands, the rate of STIs (syphilis, chlamydia, gonorrhoea) increased from 15.2 to 21.1% between 2006 and 2010 and then dropped to 18.3% in 2012 [22].

Sex workers in Canada and the USA report high levels of childhood trauma and violence, and among those with histories of violence and abuse, mental illness may be mediating the association between trauma and unprotected sex [29, 49]. Estimates of mental health issues among female sex workers vary significantly across aspects of the industry and settings, ranging from low levels to as high as 74% reporting severe depression, anxiety or post-traumatic stress [49]. Evidence suggests historical experiences of violence and indirect violence (i.e., witnessing violence) can contribute to STBBI risk by shaping the propensity to use drugs for self-treatment of emotional trauma [50].

Comorbid substance use and mental health problems among sex workers may elevate risk for violence and risk of STBBIs from partners to sex workers [45, 46, 51]. A recent study identified depression as significant predictor of unprotected anal sex with the most recent male client among MSWs who work online [52]. The majority (91%) of North American MSWs reported having sex while drunk; 32% had a history of depression; 41% had a history of childhood sexual abuse; and 79% of those who work on the street had been incarcerated [45]. One-third reported being HIV positive and one-quarter had never been tested for STIs [45]. In the UK, one-fifth of MSWs surveyed reported a history of mental illness and 21% reported a history of sexual abuse, with multivariable analyses demonstrating significant associations between injection drug use and HIV [21].

A USA-based systematic review found a high prevalence of sex work involvement among trans women, with an estimated 24–75% of trans women reported to have participated in sex work in their lifetime [53]. Among trans sex workers, low self-esteem and a history of rape was independently associated with inconsistent condom use [54], and the majority of trans women (of whom 53% reported sex work in the last 6 months) surveyed in the USA reported suicidal ideation or attempts and depression [55].

Studies describing context of promising structural-level intervention and prevention practices to reduce STBBIs among sex workers in high-income countries and policy implications are outlined in Table 4.

This review uniquely builds upon the literature and contributes to our understanding of multilevel factors that potentiate and mitigate STBBI risk among cis women, cis men, and trans sex worker populations. To the best of our knowledge, this is the first comprehensive synthesis of determinants and intervention and prevention strategies to reduce STBBI burden among sex workers of all genders, specific to high-income countries. The majority of research and data on STBBIs among sex workers are largely confined to LMICs, with a dearth of research focusing on the experiences of cis men and trans sex workers. Studies seldom disaggregate data by sex work involvement [115], which limited our ability to understand the determinants of, and interventions for, STBBIs in these populations. Given the heterogeneity of sex worker populations, and distinct vulnerabilities faced by cis men and trans sex workers, further research utilizing mixed-methods should be implemented to delineate the intersections of risk and ameliorate critical health inequalities for all sex workers.