Prevalence and correlates of Trichomonas vaginalis infection among female sex workers in a city in Yunnan Province,China

Abstract

Sexual transmission is the fastest growing route of HIV transmission in China, and Trichomonas vaginalis (TV) can facilitate HIV transmission and acquisition. Our goal was to determine the prevalence and correlates of TV infection among female sex workers (FSWs). This cross-sectional study was conducted in a city of Yunnan Province in southern China, with confidential face-to-face interviews and laboratory tests for TV (wet mount) and other sexually transmitted infections. A total of 734 FSWs participated in the study. The prevalence of TV was 9.0% (95% confidence interval [CI] 7.02–11.30). In multivariate analyses, adjusted odds ratios of TV infection were 3.0 (95% CI 1.47–6.01) for herpes simplex virus type 2 seropositive, 2.4 (95% CI 1.37–4.14) for Chlamydia trachomatis infection, 2.6 (95% CI 1.30–5.31) for genital ulcer, 1.9 (95% CI 1.11–3.30) for starting age in commercial sex <20 years, and 0.5 (95% CI 0.27–0.87) for vaginal douching. We found a relatively high prevalence of TV infection among FSWs in Yunnan Province. A range of control strategies that include TV screening are recommended among FSWs, which could contribute significantly to the disruption of transmission by the provision of immediate treatment.

Keywords

trichomoniasis sexually transmitted infections women female sex workers vaginal douching China

Background

Sexual transmission has become the primary mode of human immunodeficiency virus (HIV) transmission in China.¹ This is a problem in China as since the 1980s, commercial sex work has become increasingly prevalent.² Female sex workers (FSWs) are not only at a high risk of acquiring HIV, but are also a core group for secondary transmission to the general population, including their clients.^3–5 Sexually transmitted infections (STIs) facilitate HIV transmission through direct and biological mechanisms.^6–10 Early screening and treatments of STIs among FSWs can be a strategy for HIV prevention in China.

Trichomoniasis, one of the most common non-viral STIs, is caused by the protozoon parasite Trichomonas vaginalis (TV). TV infection is associated with serious health consequences including pre-term labour, infertility, pelvic inflammatory disease, and prenatal morbidity.^11–13 TV infection has a range of presentations, including vaginitis and malodorous vaginal discharge;¹⁴ however, it is estimated that half of women are asymptomatic.¹⁵ This is especially problematic given that TV infection had 1.5 to 2.7 times greater risks of HIV acquisition and transmission.^16–18 Among HIV-1-positive individuals, TV infection is associated with higher genital HIV-1 levels,¹⁹ and successful treatment of trichomoniasis reduced the shedding and genital HIV-1 levels.²⁰

HIV/STI prevalence levels in China in FSWs are among the highest in Yunnan Province in the south of the country, near its borders with Vietnam, Thailand, and Myanmar.²¹ However, little is known about TV prevalence among FSWs in Yunnan Province. The main goal of this study was to inform future HIV/STI prevention efforts in this high-risk area of China by assessing TV prevalence and determining the associated factors among FSWs in Yunnan Province, China. The study was conducted in a moderately-sized city in Yunnan Province, with a population of about 300,000 and nearly 1000 sex workers.

Methods

A cross-sectional study of all women identified as being FSWs was carried out in a city in Yunnan Province from September to October 2012. After receiving approval from the institutional review board of the National Center for AIDS/STD Control & Prevention, Chinese Center for Disease Control and Prevention (CDC), the study was conducted by China CDC in Beijing with provincial and local CDC staff in Yunnan. The FSWs were recruited by outreach workers from the local CDC who went to all sex work venues and explained the purpose of the study and the procedures of participation to FSWs, who were invited to participate in this study. Subjects eligible to participate in the study were those aged ≥16 years, who self-reported as having sold sex for monetary compensation within the previous three months, and who agreed to HIV and STI testing and counselling. After providing informed consent, participants were asked standard questions about their demographics, basic medical history and behavioural risk factor information by locally trained staff. Vaginal douching was defined as the practice of cleansing the vagina with a liquid solution.

During the gynecological examination, vaginal swabs were collected and a wet mount was immediately prepared to detect TV; endocervical swabs were collected and tested for Neisseria gonorrhoeae and Chlamydia trachomatis by polymerase chain reaction (PCR, AMPLICOR, Roche, USA). Blood was collected and tested for HIV-1 enzyme-linked immunosorbent assay (ELISA, Vironostika HIV Uni-Form plus O, bioMerieux, France), herpes simplex virus type 2 (HSV-2, HerpeSelect-2 ELISA IgG, Focus, USA) antibody testing, and syphilis by the rapid plasma reagin (RPR) test (Diagnosis kit, Xinjiang Xindi company, China). Positive HIV-1 ELISAs were confirmed by Western blot (Diagnostics HIV Blot 2.2, Genelabs, USA) and positive RPRs were confirmed by the Treponema pallidum particle assay (TPPA) test (Serodia-P·PA-Fujirebio, Fuji, Japan). Finally, urine was collected for opiate screening (MOP One Step Opiate Test Device, ACON Laboratories, Inc., USA). Participants were classified as using illegal drugs if they either self-reported such use or tested urine positive for opiates. All participants were scheduled for counselling on STI test results and participants with any STIs were referred for treatment to Kaiyuan City Dermatology Hospital; however, the information on medical treatment was not collected.

Statistical tests were performed using SAS™ 9.1 software (SAS Institute Inc, Cary, NC, USA). Univariate associations between risk factors and TV infection were evaluated using logistic regression analysis. Variables achieved p < 0.2 in the univariate analysis and factors deemed clinically relevant were then evaluated by stepwise logistic regression analysis limiting final multivariate models to risk factors or confounders that were statistically significant. All statistical tests were conducted based on two-tailed alternatives with significance set at the p < 0.05 level. Higher sex worker risk venues were defined as locations where FSWs generally charged less than 100 Yuan (about $16 USD) for sex services, including beauty salons, temporary sublets, and street walkers; these FSWs attracted the less wealthy and less educated clients potentially at a higher risk of HIV infection, such as drug users. Lower risk sex worker venues were defined as locations where FSWs generally charged 100 Yuan or more for sex, including karaoke clubs, night clubs, saunas, and hotels.

Results

Demographics of the study population

Of the 748 FSWs screened for the study, 14 were excluded because vaginal swabs specimens could not be obtained. All analyses were based on the final 734 FSWs. Demographic characteristics of the study population and their associations with TV infection by univariate logistic regression are listed in Table 1. These women were predominantly young with a median age of 25 years (interquartile range [IQR] 21–30 years), of Han ethnicity (69.6% [compared to the national prevalence of 92% Han]), from the local area or elsewhere in Yunnan province (79.2%), and unmarried (58.6%). The majority worked in lower risk entertainment establishments and lived independently in their own apartment.

Table 1.

Demographic factors associated with TV infection among FSWs in a city in Yunnan Province.

Factors		No. FSWs	TV positive (row %)	OR (95% CI)	p Value
Age (years)	16–20^a	168	24 (14.3)
	21–25	218	14 (6.4)	0.4 (0.21–0.82)	0.01
	≥26	348	28 (8.1)	0.5 (0.29–0.94)	0.03
Nationality	Han^a	511	42 (8.2)
Nationality	Other	223	24 (10.8)	1.3 (0.79–2.28)	0.27
Registered permanent residence	Outside Yunnan^a	153	9 (5.9)
	Local city	146	16 (11.0)	2.0 (0.84–4.61)	0.12
	Other cities in Yunnan	435	41 (9.4)	1.7 (0.79–3.51)	0.18
Education level	<9 years^a	392	36 (9.2)
Education level	≥9 years	342	30 (8.8)	1.0 (0.57–1.58)	0.85
Marital status	Single or cohabitation^a	430	43 (10.0)
Marital status	Married, separated, divorced, or widowed	304	23 (7.6)	0.7 (0.43–1.25)	0.26
Entertainment venue	Lower risk^a	477	36 (7.6)
Entertainment venue	Higher risk	257	30 (11.7)	1.6 (0.97–2.70)	0.06
Residence type	Apartment^a	504	46 (9.1)
	Family home	63	9 (14.3)	1.7 (0.77–3.58)	0.20
	Brothel or other working location	167	11 (6.6)	0.7 (0.36–1.39)	0.31

FSWs: female sex workers; TV: Trichomonas vaginalis.

Reference group.

Prevalence of TV infection and other STIs

The prevalence of TV as confirmed by wet mount was 9.0% (95% CI 7.02–11.30). Prevalence of the other STIs ranged from 5.9% to 68.5%, with HIV-1 being 11.3%. A total of 362 (49.3%) of the 734 participants were positive for one STI (not including HIV), 143 (19.5%) had two concurrent infections, and 54 (7.4%) had three or more infections. Subjects with syphilis, C. trachomatis or HSV-2 infection had a significantly higher prevalence of TV infection than those without (Table 2).

Table 2.

Sexually transmitted infections (STIs) and relevant symptoms associated with TV infection among FSWs in a city in Yunnan Province.

Type of infection	STI infection status (No. tested)	TV positive No. (%)	OR (95% CI)	p Value
Syphilis
No^a	672	55 (8.2)
Yes	62	11 (17.7)	2.4 (1.19–4.91)	0.01
N. gonorrhoeae
No^a	691	59 (8.5)
Yes	43	7 (16.3)	2.1 (0.89–4.89)	0.09
C. trachomatis
No^a	587	41 (7.0)
Yes	147	25 (17.0)	2.7 (1.60–4.66)	<0.01
HSV-2
No^a	231	10 (4.3)
Yes	503	56 (11.1)	2.8 (1.39–5.53)	<0.01
HIV-1
No^a	651	56 (8.6)
Yes	83	10 (12.1)	1.5 (0.71–2.98)	0.30

FSWs: female sex workers; TV: Trichomonas vaginalis.

Reference group.

Factors correlated with TV infection

In contrast to FSWs aged 16–20 years, FSWs 21–25 years of age (odds ratio [OR] = 0.4; 95% confidence interval [CI] 0.21–0.82) and FSWs aged ≥26 years (OR = 0.5; 95% CI 0.29–0.94) were significantly less likely to be infected by TV. There were no statistically significant differences regarding other demographic characteristics between TV-positive and TV-negative FSWs.

The behavioural characteristics and gynecological symptoms of these women and their association with TV infection by univariate logistic regression are also listed in Table 3. A total of 100 (13.6%) FSWs either self-reported illegal drug use or had a positive urine drug test, but this was not significantly associated with an increased risk for TV infection. FSWs whose starting age in commercial sex was <20 years were twice as more likely to be infected with TV compared to those whose starting age in commercial sex ≥20 years. Of note, 50% of women reported a ‘regular partner’, defined as a man with whom FSWs have a regular, non-paid sexual relationship, such as a boyfriend or spouse. The vast majority (78%) of women did not use condoms routinely with their regular partner, but there was no significant association between using condoms with regular sex partners and TV infection. Vaginal douching was very common among these FSWs (78.9%). Interestingly, the prevalence of TV was lower among FSWs who reported vaginal douching (OR = 0.5; 95% CI 0.31–0.93).

Table 3.

Behavioural characteristics and symptoms associated with TV infection among FSWs in a city in Yunnan Province.

Characteristics	FSWs No.	TV positive No. (%)	OR (95% CI)	p Value
Illegal drug user
No^a	634	52 (8.2)
Yes	100	14 (14.0)	1.8 (0.97–3.43)	0.06
Drinking alcohol
No^a	261	26 (10.0)
Yes	473	40 (8.5)	0.8 (0.50–1.40)	0.50
Age of first sex (years)
≥18^a	461	34 (7.4)
<18	273	32 (11.7)	1.7 (1.00–2.77)	0.05
Starting age in commercial sex (years)
≥20†	540	39 (7.2)
<20	194	27 (13.9)	2.0 (1.23–3.50)	<0.01
Having regular sex partners
No^a	364	37 (10.2)
Yes	370	29 (7.8)	0.8 (0.45–1.25)	0.27
Always used condom with regular partner in previous week
Yes^a	81	9 (11.1)
No	289	20 (6.9)	0.6 (0.26–1.36)	0.22
Number of clients in previous week
1^a	178	13 (7.3)
2–4	313	30 (9.6)	1.3 (0.68–2.65)	0.39
≥5	243	23 (9.5)	1.3 (0.65–2.70)	0.43
Always used condom with clients in previous week
Yes^a	636	56 (8.8)
No	98	10 (10.2)	1.2 (0.58–2.39)	0.65
Vaginal douching
No^a	155	21 (13.6)
Yes	579	45 (7.8)	0.5 (0.31–0.93)	0.03
Abnormal vaginal discharge
No^a	657	53 (8.1)
Yes	77	13 (16.9)	2.3 (1.20–4.48)	0.01
Dysuria
No^a	722	65 (9.0)
Yes	12	1 (8.3)	0.9 (0.12–7.23)	0.94
Genital ulcer
No^a	730	64 (8.8)
Yes	4	2 (50.0)	10.4 (1.44–75.12)	0.02

FSWs: female sex workers; TV: Trichomonas vaginalis.

Reference group.

In all, 10.5% (77/734) of FSWs had abnormal vaginal discharge, and these subjects had a significantly higher TV prevalence (OR = 2.3; 95% CI 1.20–4.48). Interestingly, in 42.4% (28/66) of infected women, the cervix appeared normal on speculum examination. Dysuria, a common symptom of trichomoniasis, was reported only by one (1.5%) infected woman. Genital ulcers were significantly more prevalent in women with TV infection (OR = 10.4; 95% CI 1.44–75.12).

Multivariate analyses

Table 4 displays the results from multivariate logistic regression models of TV prevalence. In the final multivariate model, HSV-2-positive FSWs were independently three times more likely to have a TV infection, compared to HSV-2-negative FSWs. Starting age in commercial sex <20 years (adjusted OR [AOR] = 1.9; 95% CI 1.11–3.30), genital ulcers (AOR = 2.6; 95% CI 1.30–5.31), and C. trachomatis infection (AOR = 2.4; 95% CI 1.37–4.14) were also independently associated with TV infection. Vaginal douching was significantly associated with an independent lower risk of TV infection.

Table 4.

Multivariate analysis of risk factors associated with TV infection among FSWs in a city in Yunnan Province.

Risk factors	Adjusted OR (95% CI)	p Value
Starting age in commercial sex <20 years	1.9 (1.11–3.30)	0.02
Vaginal douching	0.5 (0.27–0.87)	0.01
Genital ulcer	2.6 (1.30–5.31)	<0.01
HSV-2 seropositive	3.0 (1.47–6.01)	<0.01
C. trachomatis infection	2.4 (1.37–4.14)	<0.01

FSWs: female sex workers; TV: Trichomonas vaginalis.

Discussion

Overall 9.0% of the 734 FSWs included in this study were infected with TV. This result is higher than the rates reported elsewhere among FSWs,^22,23 but lower than the reported rate in a study conducted in Indonesia, which investigated STI trends and found a TV prevalence of 11% to 16%.²⁴ The prevalence of TV depends on access to health services, sexual behaviour, hygiene habits, socio-economic factors, and laboratory detection techniques.²⁵ The prevalence of trichomoniasis is often neglected because there are no readily available specific procedures for screening TV infection. The relatively high prevalence among FSWs identified in our study is an important public health concern as TV infection may facilitate HIV transmission. Understanding the prevalence of STIs, including TV, is key to characterising the Chinese HIV/AIDS epidemic and will aid in informing policy and prevention efforts that can help to protect and treat at-risk populations.³

Like other studies of Chinese FSWs,^4,26,27 we found high rates of STIs in this group as well as several significant associations between TV infection and other STIs. Substantial co-infections with C. trachomatis or HSV-2 and TV infection were shown in the study. Whether this reflects an interaction that facilitates co-infection or just represents a sub-group at a higher risk for both infections is unclear. Biological factors may help explain the association with C. trachomatis. C. trachomatis can cause pelvic inflammatory disease, cervical inflammation and other chronic inflammation of the urogenital tract, and chronic urogenital tract inflammation can contribute to the susceptibility of other microbial pathogens, including TV.^27,28 Apart from the biological mechanism, it may also be due to the fact that both infections share a common route of transmission, intersecting sexual networks, and pattern of risk factors. As there is no cure, HSV-2 is a reliable indicator of past risky sexual behaviour and such behaviours may also put individuals at risk for TV infection.

TV prevalence was higher among FSWs with genital ulcers, as they may provide a portal of entry for TV. However, there were no statistically significant differences regarding other clinical signs or symptoms between TV-positive and TV-negative FSWs. TV infections involve the characteristic frothy greenish vaginal discharge, pruritus, and dysuria. However, only 10.5% of FSWs had abnormal vaginal discharge; 42.4% of infected women had an apparently normal cervix on speculum examination, indicating that this clinical sign and symptoms have a low sensitivity. These findings highlight the need for TV screening recommendations considering the availability of affordable treatments and serious health consequences of TV infection.

Notably, there was a strong association between starting age in commercial sex and TV infection (AOR = 1.9; 95% CI 1.11–3.30). We also found that age of sexual debut <18 years increased the risk of TV acquisition (OR = 1.7; 95% CI 1.00–2.77) in the univariate analysis, although non-significant in multivariate analysis. Age at sexual debut or starting age in commercial sex could be a proxy for unmeasured factors that may be associated with increased risk of STIs, including TV infection. Early age at sexual debut or starting age in commercial sex may be associated with riskier sexual behaviour and choice of sex partners with high-risk behaviour.^3,29 Participants with early sexual debut may be more vulnerable later in life to exploitative sexual behaviour, which may increase their contact with infected partners.

Vaginal douching was practiced by 79% of the FSWs in our study, a finding consistent with results from another study of FSWs in China, which found that 65% of them douched.³⁰ We found that vaginal douching was a significant protective factor in TV infection after adjusting for other key risk factors (AOR = 0.5; 95% CI 0.27–0.87). This could be related to women douching just before participating in our study, which affected the motility of TV, especially when chemical agents were used for douching. Therefore, it should be suggested not to carry out vaginal douching before gynecological examination during TV screening. In addition, previous studies demonstrated an increased risk of HIV/STIs among FSWs who participated in vaginal douching.^26,30,31 Douching may remove normal vaginal flora and change the ecology, permitting the overgrowth of pathogens.

Our study has several limitations. First, this was a cross-sectional study, temporality could not be determined. It is impossible to determine whether TV is infected after other STIs or not among FSWs with co-infections of TV and other STIs. Although the cross-sectional design is not the best design for determining risk factors, it is justified for assessing the prevalence of TV infection and associated factors among FSWs. Second, the prevalence may be underestimated due to the low sensitivity of the wet mount techniques employed compared with nucleic acid amplification tests (NAATs) and culture. Culture is considered the gold standard in detecting TV infection. In addition, vaginal douching which may affect the motility of TV may also underestimate the prevalence of TV. NAATs should be considered to further investigate the relationship between vaginal douching and TV infection in future studies. Third, similarly, false-negative results for both RPR and TPPA tests may result in an underestimation of syphilis as some subjects may have been in early or late stages of syphilis. At last, some risk factors based on self-report, such as use of condoms and drug use, may have been misclassified. To minimise this effect, we asked questions about recent events, such as condom use in the previous week.

Conclusions

In summary, we found that the prevalence of TV infection was relatively high among FSWs in Yunnan Province. Since most TV infections are asymptomatic, a range of control strategies that include TV screening and the use of rapid point-of-care tests among FSWs could contribute significantly to the disruption of transmission by the provision of immediate treatment. In addition, education on the importance of diagnosis, treatment, and prevention may help control the spread of TV infection.

Footnotes

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was funded by a grant from the National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health (U19 AI51915-05).

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