Introduction

Engaging in heterosexual anal sex (HAS) is not an uncommon behavior among women worldwide (Karamouzian et al. 2019; Owen et al. 2019; Hess et al. 2016). In the context of sexually transmitted infections (STIs), the likelihood of HIV transmission through HAS is significantly higher than that of vaginal sex due to the fragile nature of rectal mucous membranes that are rich in blood vessels (Dal Pogetto et al. 2012; Baggaley et al. 2010). Moreover, condomless HAS and condom breakage are frequent during HAS (Owen et al. 2019; Alexander et al. 2014). HAS is of particular concern among marginalized populations including female sex workers (FSWs) who often face demands for HAS and condomless sex from their clients (Alexander et al. 2014).

Studies suggest that the pooled prevalence of ever engaging in HAS among FSWs is around 15.7% (Owen et al. 2019). Moreover, FSWs are concurrently exposed to multiple high-risk behaviors such as HAS, substance use, and multi-partner sex (Risser et al. 2009). Indeed, FSWs who engage in HAS, often have a higher risk profile (e.g., longer sex work career, higher number of clients, frequent alcohol consumption, and inability to negotiate condom use) than those who avoid practicing HAS (Duby and Colvin 2014; Alexander et al. 2014). Moreover, HAS may be practiced among FSWs during menstruation periods or in the presence of vaginal infections. Other motives for practicing HAS include financial incentives provided by the clients as well as misconceptions regarding the necessity of condom use during HAS (Duby and Colvin 2014).

In Iran, FSWs are the second most-affected key population at risk of HIV, after people who inject drugs (Sharifi et al. 2018). While sex work is highly stigmatized and criminalized in Iran, recent population size estimations suggest that over 220,000 FSWs live in urban settings in Iran (Sharifi et al. 2017). Although FSWs were tolerated before the 1979 Islamic revolution and their activities were limited to certain neighborhoods, sensitivities around sex work have been historically present and are deeply rooted in the socio-cultural and religious context of Iran as a Muslim majority setting. After the Islamic revolution, the government’s policy about sex workers changed and sex work was deemed illegal and punishable by law (Rostamzadeh et al. 2016; Karamouzian et al. 2016a, b). However, the practice of “Sigheh” or temporary marriage where men could marry unmarried women for a fixed term and a pre-determined amount of money is legal; a phenomena that further complicates the sex work landscape in Iran and renders some sex work practices legal (Rostamzadeh et al. 2016; Karamouzian et al. 2020).

Despite the socio-cultural sensitivities around sex work in Iran and FSWs’ increased risk of HIV due to the intersecting structural inequities (e.g., poverty, stigma, discrimination, and sex work criminalization) that create barriers in their access to HIV/STIs prevention, care, and treatment services (Hamzić and Mir-Hosseini 2010; Mohebbi 2005; Karamouzian et al. 2020), they are provided with harm reduction services, including HIV testing and counseling, sexual health education, as well as free condoms and needles through over 60 centers for vulnerable women established across the country (Karamouzian et al. 2017a). These centers have helped improve our understanding of FSWs’ sexual and reproductive health characteristics (e.g., condom use practices, STIs, and abortion) across different provinces (Khezri et al. 2020; Karamouzian et al. 2017b; Sajadi et al. 2013; Shokoohi et al. 2017; Shahesmaeili et al. 2018). However, our understanding of the dynamics of high-risk sexual practices such as HAS among FSWs in Iran remains limited. Given the vulnerabilities associated with HAS among FSWs, this study aims to assess the prevalence and correlates of recent HAS practices among FSWs in Iran, to help inform sex work harm reduction efforts and reduce the burden of HIV/STIs among FSWs.

Methods

Study Design and Setting

Between January and August 2015, we recruited 1347 FSWs from facility-based centers as well as outreach spots in 13 major cities, representing different geographical regions of Iran. The cities included: Ahvaz (southwest), Arak (central), Bandar-Abbas (south), Isfahan (central), Kerman (southeast), Kermanshah (west), Khorramabad (west), Mashhad (northeast), Sari (north), Shiraz (south), Tabriz (northwest), Tehran (the Capital, central), and Zahedan (southeast). The facilities provide harm reduction services (e.g. HIV testing, counselling services, and access to free condoms) for vulnerable women (i.e., women who are involved in sex work, use/inject illicit drugs, or have a history of incarceration) (Fahimfar et al. 2013). These facilities are run by non-governmental organizations (NGOs) under the supervision of the Ministry of Health and the Social Welfare Organization (SWO). Selection of the harm reduction facilities was informed by the recommendation of the HIV/STIs office located at the Ministry of Health as well as the provincial departments of health based on the number of FSWs registered in each facility and the facilities’ logistics and capacity constraints. The majority of FSWs (n = 1198; 89%) were recruited using convenience sampling inside the facilities where peer FSWs approached potential participants and sought their interest in taking part in the survey after providing them with an overview of the study’s objectives and procedures. A smaller group of FSWs (n = 149; 11%) were recruited from street-based venues by peer-led outreach teams.

Eligibility Criteria

Eligibility criteria for this study were being female, ≥ 18 years old, having engaged in any kind of penetrative sex (i.e., vaginal, oral, anal sex) with more than one male client in previous 12 months in return for money, goods, services, or drugs, having Iranian nationality, and residing or working in the city that the study was being conducted in.

Data Collection

After providing verbal informed consent, FSWs were interviewed individually in a private room by a trained and experienced female interviewer. We applied a standard behavioral risk assessment questionnaire for data collection. The questionnaire had various sections such as demographic characteristics, sexual behaviors, HIV testing and sero-status, and history of substance use and injection drug use. We assessed HIV sero-status by applying HIV and syphilis rapid test (SD BIOLINE HIV/Syphilis Duo rapid test, Standard Diagnostics Inc., Gyeonggi-do, South Korea) and a confirmatory test (Unigold). The interviews lasted for less than an hour. The project manager visited each recruitment site at least once during the data collection phase to ensure data collection protocols were closely followed. We provided FSWs with a monetary incentive for the interview (70,000 Rials equivalent to ~ 2 USD) and for the HIV test (30,000 Rials equivalent to ~ 1 USD).

Measures

Dependent Variables

The dependent variable of interest was engaging in HAS during the previous month. FSWs who had ever had HAS during their lifetime were asked whether they had engaged in HAS in the previous month (Yes vs. No).

Covariates

Data were collected on socio-demographic characteristics, including age, type of recruitment (outreach or facility-based), length of sex work career (i.e., duration between the date of sex work debut and the interview date [< 1 year, 1–5 years, or > 5 years]), marital status (single, married, “sigheh” [i.e., temporary marriage], or divorced/widowed), highest level of education (≤ primary school, secondary school, or ≥ high school diploma), having sources of income other than sex work (yes or no), housing status (stable or unstable [i.e., living primarily in shelters or on the street]), primary client finding pattern (street [i.e., streets, shopping malls, parks, and public transit], independent [i.e., cell-phone, parties, online, and fixed clients]), or brothels [i.e., underground houses controlled by pimps referred to as “Khaane-Teami”], lifetime history of rape (yes or no), and HIV comprehensive knowledge, measured by asking five questions on HIV transmission and misconceptions. We also measured FSWs’ HIV risk perception, measured by asking FSWs how much they perceived themselves to be at risk of HIV (low-moderate or high), number of paying and non-paying partners during the previous month (0, ≤ 10, or > 10), history of group sex during the previous year (yes [i.e., having had sex with multiple clients at the same time] or no), condom use with non-paying partners and with clients during last sex (yes or no), and lifetime history of injection drug use (yes or no). Furthermore, we obtained information on history of HIV test (yes or no), self-reported HIV status (positive, negative or don’t know), prior STIs during last year (yes or no), alcohol use during last month (none, < weekly, or at least weekly), current drug use (none, only stimulants, only opioids, or polysubstance use [i.e., opioids and stimulants]), and sex under the influence of drugs/alcohol during the previous month (yes or no). Covariate selection was informed by Tim Rhodes’ risk environment framework (Rhodes 2002) and previous studies assessing sexual risk behaviors among FSWs (Maheu-Giroux et al. 2018; Ramanathan et al. 2014; Longo et al. 2017).

Statistical Analysis

Descriptive statistics for all continuous and categorical variables were reported. Given the prevalence of the outcome of interest (i.e., > 10%), we constructed  bivariable and  multivariable modified Poisson regression using a generalized linear model (GLM) with Poisson as family and log link function (Zou 2004) to identify the correlates of having HAS in the previous month. Variables with a P value < 0.2 in the bivariable regression were entered into the multivariable regression model. Potential multicollinearity was examined using the variance inflation factor (VIF), and no multicollinearity was detected (Mean VIF: 1.84) (Dormann et al. 2013). Stata’s survey package was used to adjust for clustering effects. The final model was selected using a backward selection approach based on the lowest Akaike’s Information Criterion (AIC). Crude and adjusted prevalence ratios (APRs) along with their 95% confidence intervals (CI) were reported. All statistical analyses were performed using Stata v.15 (Stata Corp., College Station, Texas) and P values less than 0.05 were considered statistically significant.

Results

A total number of 1337 of FSWs who provided valid responses to the dependent variable of interest were included in the analysis. The mean age of FSWs was 35.3 (standard deviation = 8.8) years; 137 (10.3%) were younger than 25 years old. Overall, 507 (37.9%) had ≤ primary school education, 590 (44.2%) were divorced/widowed, 788 (59.2%) had no other source of income than sex work, 662 (50.0%) found their clients on the street, 1200 (89.8%) had stable housing, and 118 (14.5%) had initiated their sex work career before the age of 18.

We found that 658 (49.2%) of FSWs had a lifetime experience of HAS; most of whom (61.2%; n = 403) reported monetary incentives provided by the clients as their main reason for engaging in HAS. Overall, 247 FSWs (18.5%; 95% CI: 13.0, 25.6) had engaged in recent (i.e., last month) HAS. Demographic and behavioral characteristics of the participants stratified by recent HAS are presented in Table 1.

Table 1 Demographic and behavioral characteristics of female sex workers stratified by recent heterosexual anal sex practices
Full size table

Among the 247 of FSWs who had engaged in recent HAS, 51.9% (n = 119) had used condoms with their last client (i.e., paying partner), and 28.7% (n = 56) had used condoms with their last non-paying partner. Moreover, 80% (n = 196) reported inconsistent condom use during HAS in the previous month, 87.1% (n = 197) had received free condoms from health centers in the last year, and 61.5% (n = 125) could obtain/buy condoms in less than an hour if needed.

The findings of the multivariable analysis are presented in Table 2. In the multivariable modified Poisson regression model, recent HAS was positively associated with younger (≤ 18) age at sex work debut (APR: 1.24; 95% CI: 1.06–1.59), history of group sex in the previous month (APR: 1.62; 95% CI: 1.08–2.44), higher number of clients in the previous month (APR: 2.35; 95% CI: 1.38–4.00), and frequent alcohol use (APR: 1.62; 95% CI: 1.12–2.34). Moreover, recent HAS was negatively associated with being married (APR: 0.52; 95% CI: 0.34–0.80) or divorced (APR: 0.50; 95% CI: 0.30–0.81) and having used condoms with their last client (APR: 0.73; 95% CI: 0.54–0.97).

Table 2 Correlates of involvement in recent heterosexual anal sex in female sex workers in Iran
Full size table

Discussion

We found that about one in five FSWs had recently engaged in HAS, most of whom reported inconsistent condom use during their last-month HAS practices. Also, HAS among FSWs was positively associated with being single, younger at sex work debut, and engaging in risky behaviors such as group sex, higher number of clients, and frequent alcohol use. It was also interesting to see that most FSWs knew that HAS carries a high risk for HIV transmission. The frequency of HAS among our participants is consistent with the findings of recent studies elsewhere (e.g., 20% among Ivorian FSWs in 2018 (Maheu-Giroux et al. 2018), 22% among Indian FSWs in 2014 (Ramanathan et al. 2014), and 19% among FSWs in the Central African Republic in 2017 (Longo et al. 2017)). Older studies however, have reported lower prevalence of anal sex (e.g., 0.03% among Indian FSWs 2005 and 2.1% among Bangladeshi FSWs 2006) which could be due to HAS-related stigma and recent increasing practices of HAS among heterosexual populations (Tucker et al. 2012; Owen et al. 2019).

FSWs with inconsistent condom use were more likely to have practiced HAS. The considerable frequency of unprotected HAS among FSWs in Iran might reflect the fact that some FSWs may not view anal intercourse as a risky sexual behavior (Mirabi et al. 2013), are unaware of the transmission of HIV/STIs through HAS, or lack condom negotiation skills (Tucker et al. 2012; Mirabi et al. 2013). This finding is of particular concern as unprotected HAS is associated with the highest risk of transmission of HIV compared to vaginal or oral sex (Dal Pogetto et al. 2012). Harm reduction and condom promotion efforts need to further highlight the risks associated with HAS and re-emphasize the importance of safe sex among FSWs as well as the general public who are potential clients of FSWs. It is also essential to ensure FSWs are provided with condom negotiation skills as most reported monetary incentives as the primary reason for consenting to HAS with clients.

Prevalence of HAS among single FSWs was higher than married, divorced or widowed FSWs. Indeed, not being single (married, widowed, and divorced) reduced the frequency of HAS by about 50%. Previous studies have shown significant positive effects of marriage in a number of health behaviors (Tucker et al. 2012; Alexander et al. 2014; Stein et al. 2007). This possible impact could be partly explained by the marriage selection and protection mechanisms where healthier people are more likely to get married and marriage providing a shield against risky behaviors (e.g., unhealthy diet, smoking, drinking, and high-risk sex) as well as offering a supportive relationship and economic benefits (Prior and Hayes 2001). Furthermore, the high frequency of HAS in single FSWs in Iran may be due to the concerns about getting pregnant (Karamouzian et al. 2017b), and having to potentially deal with unintended pregnancies and abortion, which is indeed criminalized in Iran, unless there is a serious fetal abnormality or a life-threatening medical condition for the mother (Karamouzian et al. 2016b; Motaghi et al. 2013; Erfani 2011).

Prevalence of HAS among FSWs who initiated sex work before the age of 18, was significantly higher than those who initiated sex work after the age of 18. Initial sexual experiences are considered as vital life events that may affect future sexual behaviors and several studies have highlighted the relation between early sexual experiences and high-risk sexual behaviors in adulthood (Cavazos-Rehg et al. 2010; Magnusson et al. 2012; Khezri et al. 2020). Although the mechanism of this relationship is unclear (Magnusson et al. 2015), some studies have also discussed the role of sensation-seeking and impulsivity in the first sexual relationship (Khurana et al. 2012), or how early sexual experiences may form a basis for interpersonal scripts for subsequent sexual behaviors (Simon and Gagnon 1986).

We also observed FSWs with certain high-risk sexual behaviors (e.g., group sex) were more likely to engage in HAS. Studies suggest the frequency of HAS among people who engage in group sex to vary between 25% and 55%; most of which are indeed unprotected (Phillips et al. 2014). Engaging in group sex has also been associated with the use of psychoactive drugs for increased sexual desires or performances (van den Boom et al. 2016). However, information on group sex activities and its effects on individuals is very limited, especially in countries with conservative socio-cultural contexts such as Iran (van den Boom et al. 2016). FSWs with higher number of clients during the previous month were also more likely to have engaged in HAS. This finding is in line with that of several other studies that have also shown HAS to be often associated with other high-risk sexual behaviors, such as multiple sexual partners at the same time, sex trade, and the use of alcohol and other drugs (Baggaley et al. 2010; Baldwin and Baldwin 2000). Indeed, frequency of HAS was higher among FSWs who engaged in sexual behaviors after drug use and frequent alcohol use. Other studies have also shown that substance use among FSWs and their partners has been associated with high-risk sexual behaviors, such as HAS and unprotected sex (Li and McDaid 2014; Buffin et al. 2014). Although the relationship between alcohol use and high-risk sexual behaviors in some studies have been strongly questioned due to methodological constraints that have failed to control for confounding factors such as sensation seeking (Woolf and Maisto 2009; Buffin et al. 2014), our findings support the findings of other studies that associate increasing prevalence of HAS with prior alcohol use (Buffin et al. 2014; Li and McDaid 2014).

We acknowledge three main limitations of our study. First, the design of the study was cross-sectional which limits causal inference. Second, given the context of the study and the marginalized nature of the participants, reporting and social desirability biases cannot be ruled out. However, we tried to measure more recent behaviors to reduce reporting and recall biases. Lastly, we were unable to recruit a random sample of FSWs which may provide a more representative sample of FSWs in Iran.

Conclusion

Evidence from the present study helped  estimate the prevalence of HAS among FSWs. We found that about one in five FSWs reported recent HAS practices, a behavior that was more frequent among single, younger, and higher risk FSWs. Since HAS may substantially contribute to HIV epidemics among FSWs and their sexual partners, interventions to empower FSWs to adopt safer sexual behaviors (e.g., condom negotiation skills) must be designed and included in initiatives of care provided to them to help address the high prevalence of unsafe HAS for both FSWs and their partners/clients.