Prevalence of Chlamydia trachomatis in women attending sexually transmitted disease clinics in the Colombo district, Sri Lanka

doi:10.4103/0377-4929.130898

Home

About us

Instructions

Submission

Advertise

Contact

e-Alerts

Users Online: 42

Impact Factor^® for 2010 is 0.57 Click here to download free Android Application for this and other journals Click here to view optimized website for mobile devices Journal is indexed with MEDLINE/Index Medicus, PubMed and Science Citation Index Expanded

Share on facebook Share on twitter Share on citeulike Share on google Share on linkedin More Sharing Services


ORIGINAL ARTICLE

Year : 2014 | Volume : 57 | Issue : 1 | Page : 55-60

Prevalence of Chlamydia trachomatis in women attending sexually transmitted disease clinics in the Colombo district, Sri Lanka

Gunasekera Henadira Appuhamilage Kamani Mangalika¹, Silva Koththigoda Cankanamge¹, Dhammike Priyadarshana², Prathapan Shamini³, Mananwatte Sujatha⁴, Weerasinghe Geeganage⁴, Abeygunasekera Nalaka⁵
¹ Department of Microbiology, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka
² Department of Gynaecology and Obstetrics, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka
³ Department of Community Medicine, Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka
⁴ National STD/AIDS Control Program, Colombo South Teaching Hospital, Sri Lanka
⁵ STD Clinic, Colombo South Teaching Hospital, Sri Lanka

Click here for correspondence address and email

Date of Web Publication

17-Apr-2014

Abstract

Background: In Sri Lanka little is known about the prevalence of Chlamydia trachomatis (CT) infection. Objective was to determine the prevalence of CT in female patients attending sexually transmitted disease (STD) clinics in the Colombo district. Materials and Methods: A descriptive cross-sectional study was carried out for the prevalence of CT in all female patients (n = 168) more than 18 years of age, attending two STD clinics in the Colombo district from January to May 2012. Endocervical swabs were collected and tested for CT using the Amplicor CT/NG polymerase chain reaction assay. Results: Prevalence of CT in females attending the STD clinics in the Colombo district was 8.3%. Mean age of those infected with CT was 32.9 years (SD ± 8.2). Majority of females with CT infections were Sinhalese and married. There was no significant association with age, ethnicity or being married or not. Females who did not attend school, or had their education only up to Grade 5 were significantly found to have six times the risk of having CT infection (95% CI = 1.8-22.6). A significant association was found with number of sexual partners but not with commercial sex work or past history of STD. Conclusions: Prevalence of CT was moderately high in this population.

Keywords: Chlamydia trachomatis, female, polymerase chain reaction, Sri Lanka

How to cite this article:
Mangalika GK, Cankanamge SK, Priyadarshana D, Shamini P, Sujatha M, Geeganage W, Nalaka A. Prevalence of Chlamydia trachomatis in women attending sexually transmitted disease clinics in the Colombo district, Sri Lanka. Indian J Pathol Microbiol 2014;57:55-60

How to cite this URL:
Mangalika GK, Cankanamge SK, Priyadarshana D, Shamini P, Sujatha M, Geeganage W, Nalaka A. Prevalence of Chlamydia trachomatis in women attending sexually transmitted disease clinics in the Colombo district, Sri Lanka. Indian J Pathol Microbiol [serial online] 2014 [cited 2014 Apr 23];57:55-60. Available from: http://www.ijpmonline.org/text.asp?2014/57/1/55/130898

Introduction

Colombo, situated on the West Coast, is the industrial, financial and commercial capital of Sri Lanka. The central clinic of the National STD/AIDS Control Program (NSACP) and the STD clinic of Colombo South Teaching Hospital (CSTH) are the only centers in the Colombo district that are funded by the Ministry of Health and provide free healthcare for STDs. Colombo district has a population of 2,344,209 of which 52.8% are females between the age of 15-49 years. ^[1]

There is limited data on chlamydial STDs in many developing countries ^[2] including Sri Lanka. The lack of cost-effective diagnostic kits/methods for Chlamydia trachomatis (CT) infections has curtailed our ability to screen our population, and prevalence studies have not been possible. Many developed countries have established a national standard plan for screening of CT infections, but in hospitals and clinics in Sri Lanka there is no program for screening. Laboratory diagnosis of CT is not done routinely in our country. Therefore, treatment for CT is done after exclusion of other possible etiologies for cervicitis and symptoms. Both clinics included in this study follow the same diagnostic and treatment protocols in keeping with national guidelines.

Commercial sex is illegal in Sri Lanka. Female sex workers and their male clients have been identified worldwide as a core group of high-frequency transmitters that play a dominant role in the transmission of HIV and other STDs. ^[3] In Sri Lanka, although studies have been done on other STDs, little is known about the prevalence of CT infections.

World Health Organization (WHO) in 2008 estimated that 498.9 million new cases of bacterial and protozoal STDs occur annually worldwide. 105.7 million cases of CT occurred worldwide, and 78.5 million of those new cases occurred in South and Southeast Asia (SEA). ^[4]

Surveillance of STDs is necessary to estimate the burden of disease, allocate resources effectively, and evaluate control strategies. From 2005 to 2011, the number of reported cases of non-gonococcal urethritis/non-gonococcal cervicitis has not changed significantly during this period (Strategic Information Management Unit, NSACP, Sri Lanka, personal communication, May 1, 2013).

Approximately 70% of women and 50% of men have asymptomatic CT urogenital infections, ^[5] which represents a huge population of untreated individuals who can unknowingly transmit the organism. Untreated CT infections could lead to pelvic inflammatory disease, ectopic pregnancies and infertility. Cervicitis caused by CT in pregnancy may result in miscarriage or premature delivery. Infection of the newborn during delivery may lead to pneumonia or conjunctivitis. ^[5] CT has also been implicated in invasive squamous cell carcinoma of the uterine cervix ^[6] and as a risk factor in HIV-1 infection and transmission. ^[7] It also influences the development of human papillomavirus-induced adenocarcinoma. ^[8]

The aim of our study was to determine the prevalence of CT in all female attendees of STD clinics in the Colombo district.

Materials and Methods

Design

A descriptive cross-sectional survey was carried out among females attending two government STD clinics in the Colombo District; namely Central STD clinic Colombo and STD clinic CSTH. A standardized questionnaire with close ended questions was administered by face-to-face interview which addressed socio-demographic characteristics and symptoms. A subsequent self-administered questionnaire (privacy was ensured by providing a box in which questionnaires could be placed anonymously) explored questions on history of STD and number of sexual partners. The questionnaire was developed in English, translated to Sinhala and Tamil and pre-tested before use.

Study population

The study population comprised of all consenting females over the age of 18 years who had not taken any antibiotics during the last 3 weeks and in whom a speculum examination was possible. All consecutive females attending the above clinics during January to May 2012 were invited to participate until the sample size of 168 was reached. Eligibility of the potential study participants was checked and written or verbal informed consent was obtained by the medical officers responsible for data collection of the study.

Data and specimen collection

After the interview, the participants were asked to provide samples for Chlamydial testing. STDs that were detected during the examination were immediately treated free of charge. After the results of the PCR were known, participants who needed additional treatment were contacted and invited to the health facility.

The definition of "sexual worker" was those who voluntarily provided information of selling sex part time or full time, as a means of making a living.

All study participants received a physical and pelvic examination. A patient was considered to have cervicitis if the clinician found: Cervical discharge and/or cervical friability.

An endocervical swab was collected through a speculum during pelvic examination by a medical officer. Endocervical swabs were collected by inserting a cotton wool swab 2 to 3 cm into the cervical os and rotating for 5 to 30 seconds. The swab for the polymerase chain reaction (PCR) was placed immediately in sucrose phosphate glutamic acid medium (SPG).

Specimens were collected daily from both STD clinics and transported at room temperature to the laboratory for processing. Upon receipt, specimens were stored at –70 ^o C until tested.

Laboratory method

For diagnosis of CT, endocervical specimens were tested using Amplicor CT/NG Test (Roche Molecular Systems, Inc., Branchburg, NJ, USA) using the Amplicor CT Detection Kit, in accordance with instructions of the manufacturer.

As part of the routine investigations carried out on these patients, high vaginal swabs were examined for bacterial vaginosis (by clue cells), candida (Gram stain) and Trichomonas vaginalis (wet mount). Results of these investigations were extracted from the laboratory records.

Statistical analysis

Data were entered in Epi-Info 3.4.3 (CDC, Atlanta, USA). The statistical analysis was performed with SPSS 15. Descriptive statistics was performed initially followed by Odds ratio (OR) and 95% confidence intervals (CI). The chi-square test was used to describe the associated factors in the categorical variables. All inferential statistics was tested at 5% significance (P < 0.05).

Ethical considerations

Study protocols, questionnaires and consent forms were approved by the Ethics Review Committee of the Faculty of Medical Sciences, University of Sri Jayewardenepura, Sri Lanka. Questionnaires and specimens were coded. This code was written on the consent form in order to identify the participant to whom the STD test results belonged. Only the team of principal investigators had access to nominal information. Some provided written consent to the study and others verbal consent. Participants who were found to be positive for CT were traced and offered the appropriate treatment.

Results

Among the 168 sampled during January to May 2012 at the STD clinics in the Colombo district, 8.3% (n = 14) of the female attendees were found to be positive with CT. The internal control revealed that seven specimens were inhibitory and required repeat testing but could not be tested except for one. Therefore, three (1.8%) were presumptively negative for CT according to manufacturer's guidelines on interpretation.

The age of all females studied ranged from 18 to 57 years. The 14 females who were CT positive ranged from 21 to 52 years with a mean age of 32.9 years (SD ± 8.2; [Table 1]). In our study population patients under the age of 18 years were not included and there were only eight patients under the age of 20 in the study group. There was no significant association between age and CT infection [Table 1].

Table 1: Association between Chlamydia trachomatis

infection and demographic characteristics

Click here to view

Majority of the females with CT infections were Sinhalese and married. There was no significant association with being Sinhalese or married. Nearly 30% of the females who did not attend school, or had their education only up to Grade five were found positive for CT and were significantly found to have six times the risk of having CT infection (95% CI = 1.8-22.6; [Table 1]).

Among the 26 females who claimed to be commercial sex workers (CSWs), 15% were found to be positive with CT infection but there was no significant association with being a CSW [Table 2]. Fourteen percent of those who had more than two sexual partners were infected with CT and they were significantly found to have three times the risk (OR = 3.2; 95% CI = 1.03-10.14) of having the infection than those with a single partner in a lifetime [Table 2].

One of 13 (7.7%) CT positives (information was missing for one CT positive patients) had an STD in the past, but past history of STD was not significantly associated with CT infection in this population [Table 2].

Table 2: Association between Chlamydia trachomatis infections and sexual behaviour

Click here to view

The most frequent reason given for visiting the STD clinic was being symptomatic (55.4%). Other reasons given were 13.1% for a medical check-up, 11.9% because the partner was infected and 4.2% for follow up. Among other reasons given for visit (14.9%) most were court referrals.

The main physical complaint was vaginal discharge among the female attendees (n = 55) and among those with CT infection (n = 7). Only 17.2% (5/29) of patients found to have a cervical discharge by the physician were positive for CT (information about discharge was missing for one CT positive patient). A complaint of discharge as well as the physical finding of a cervical discharge were significantly associated (P = 0.001 and P = 0.01, respectively) with CT positivity [Table 3]. In our study 35.7% of females found positive for CT were asymptomatic.

Table 3: Association between Chlamydia trachomatis infections and signs and symptoms

Click here to view

If the definition for cervicitis is considered as cervical discharge and/or cervical friability 14.7% of patients with cervicitis were infected with CT and this was statistically significant (P = 0.03).

The rate of co-infection of CT with Candida based on routine clinical investigations and available reports was 4.5% [Table 4]. There was no co-infection detected with trichomoniasis or bacterial vaginosis. Patients diagnosed with other STDs apart from CT based on available laboratory reports were gonorrhea (1.2%), syphilis (7.7%), trichomoniasis (0.6%), vulvo-vaginal candidiasis (13.1%) and bacterial vaginosis (4.1%).

Table 4: Chlamydia trachomatis infections and other infections

Click here to view

Discussion

Prevalence of CT was moderately high (8.3%) in this population of female STD clinic attendees. Prevalence rates of CT from studies carried out during 2000-2012 in female STD clinic attendees have been summarized in [Table 5]. As can be seen from the table, prevalence of CT in our population is comparable with prevalence in Sweden but is much lower than those in other Asian countries.

Table 5: Chlamydia trachomatis prevalence studies* among sexually transmitted disease clinic attendees, 2000-2012

Click here to view

Based on an estimated CT infection rate of 5% among American women of reproductive age, the Centre for Disease Control recommends that pregnant women be screened for CT during their first prenatal visit; and women at increased risk for infection (those with new or multiple sex partners and those under 25 years of age) be screened again during the third trimester. ^[15] The prevalence of curable STDs is considered a biological marker of sexual behavior in that community. Considering the high prevalence in our study population, screening at STD clinics may be of value. However, the high cost of commercially available diagnostic tests is likely to make this difficult to implement.

Because of the stigma associated with STDs, some individuals with symptomatic STDs are reluctant to seek treatment from government clinics. One of the limitations of our study was that it was conducted in two government clinics and did not include the several private clinics in the district.

It was noted that 35.7% of females found positive for CT were asymptomatic in this study. The majority of patients in our study visited the clinics because they were symptomatic but it is a well-known fact that up to 70% of CT-infected females are asymptomatic. ^[5] Those who are asymptomatic are unlikely to seek any kind of treatment and repeatedly expose their partners to infection. A study among the general population including asymptomatic women although desirable would have been difficult to conduct due to social, ethical and religious issues in our country. Despite these two limitations that might have lead to an underestimation of the true burden of infection in our community we have shown for the first time that the prevalence of CT infection is quite high among women of our community.

In our study only 14.7% cases of cervicitis were due to CT. This raises the question as to the etiology of the rest of the cases of cervicitis. Mycoplasma genitalium (MG) has been found to be an increasingly important cause of cervicitis in other countries, ^[3] but we have no information on how much it is responsible for cervicitis in our patients. Recent limited data indicate that antibiotics used to treat CT and NG may not be effective in all cases of MG. ^[3] Surveillance data indicates that Herpes simplex virus (HSV), a known causative agent of cervicitis, is the leading cause of STDs ^[16] in Sri Lanka. However, we do not have any data regarding the prevalence of HSV or other pathogens like ureaplasma in women with cervicitis.

The inhibition rate for the PCR reaction was 4.2% which is consistent with other studies. ^[17] It is interesting to note that although blood is considered as having inhibitory factors for PCR ^[18] none of the seven specimens that were visibly blood stained was inhibited. It was observed that the specimens that were inhibited were those that had mucus in it. Wiping the cervix before collection of the endocervical specimen as recommended by the manufacturer is important to avoid getting inhibitory results.

Although the manufacturers recommend using Dacron swabs with the Amplicor CT/NG kit, we had to use commercially available cotton wool swabs with plastic handles due to financial constraints. Soon after collection of the specimen, swabs were placed in SPG medium. Prior testing of the positive control with cotton wool swabs showed that there was no inhibition of the PCR and that the required optical density readings were achieved with the positive and negative controls.

Screening of urine is a convenient non-invasive method for detection of these pathogens. Amplicor CT/NG kit has sensitivities ranging from 79.2% to 90.7% for detection of CT in female urine with specificities of 97.0-99.4%. ^[19] Although the difference may be small, endocervical swab specimens are superior in performance to urine specimens with diagnostic tests for CT. ^[19] Therefore, it was decided to use endocervical swabs in this study to obtain a more accurate prevalence rate.

Infection with CT has been shown to be associated with certain risk factors. Younger age has been shown to be a risk factor for CT infection and age less than 20 and 30 have been implicated as the high prevalence ages. ^[12],[20] In our study we could not find any association with any age groups [Table 1]. However, it must be noted that our population consisted of patients over the age of 18 years.

Some studies show that being single is a risk factor for CT infection ^[21],[22] whereas others could not find a significant association. ^[12],[17] A low level of education was a risk factor in some ^[21],[23] but others have found no association. ^[12],[2] One study linked high literacy rate as a risk factor for CT infection. ^[25] We did not detect an association with being single which included never married, divorced or widowed women [Table 1]. Those who had studied up to Grade five or less were more at risk of infection indicating that in our women the level of education did have an impact on the prevalence of CT [Table 1].

Similarly, the number of sexual partners has also been studied as a risk factor for CT infection. Significant associations were found in some studies ^{[17],[23],[24]} while others could not find any association. ^[26] In our study CT infection was more (OR = 3.2; 95% CI = 1.03-10.14) in those who had two or more partners in the past [Table 2]. Commercial sex work and a past history of STD were not associated with CT in this study [Table 2] although it has been shown to be in some. ^[11],[27]

Religious and social ethics discourage open discussion of sexual matters in Sri Lanka. Although participants were assured of anonymity and confidentiality and given a self-administered questionnaire, the number admitting to having had more than one partner and commercial sex may be under-reported here.

A review of studies on STD rates around the world has emphasized that women selling sex tend to have comparatively higher rates of STD than the general population. ^[28] One recent study found that consistent condom use was low with only 38% brothel workers and street workers in Colombo, Sri Lanka using condoms always. ^[29] This is a cause for concern as FSW are believed to be the core in spreading infection in the community. Only 28.6% of CT-infected patients admitted to being FSWs. Therefore, it appears that in our community FSWs are not the only important source in spread of infection.

The most frequent reason given for visiting the STD clinic was being symptomatic and this is similar to findings in other studies among STD clinic attendees. ^[24] A significant association with features of cervicitis and CT positivity has been shown in other studies too [Table 3]. ^[24]

Recommendations

In conclusion the high CT prevalence rate in our study population is a cause for concern. The cost effectiveness of initiating a screening program for women of reproductive age should be considered and the search for developing cheaper diagnostic methods for CT should be continued.

Acknowledgements

Authors would like to thank the participants of the study. They wish to extend their special thanks to Mrs. Hemali Attanayake, Medical Laboratory Technologist, NSACP, for excellent technical assistance. They are thankful for the assistance in data and specimen collection, provided by Dr. A.T. Pinidiyapathirage, Dr. Hemantha Weerasinghe and Dr. K.G.S. Gunasekera of the Central clinic, National STD/AIDS Control Program and the staff of the STD Clinic, Colombo South Teaching Hospital. They also thank Mr. Wasantha Arunasiri (Computer analyst) and Dr. Sajith Dissanayake Dept. of Microbiology, Faculty of Medical Sciences, University of Sri Jayewardenepura for assistance in data entry.

References

1.	Demographic and Health Survey 2006/07. Colombo district bulletin (Provisional data). [Dept. of Census and Statistics website] Available from: statistics.sltidc.lk/index.php/ddibrowser/1300/download/7792. [Last accessed on 2013 May 21].
2.	Dean D. Chlamydia trachomatis today: Treatment, detection, immunogenetics and the need for a greater global understanding of chlamydial disease pathogenesis. Drugs Today (Barc) 2009;45 (Suppl B):25-31. [PUBMED]
3.	Gaydos C, Maldeis NE, Hardick A, Hardick J, Quinn TC. Mycoplasma genitalium as a contributor to the multiple etiologies of cervicitis in women attending sexually transmitted disease clinics. Sex Transm Dis 2009;36:598-606.
4.	World Health Organization 2012. Global incidence and prevalence of selected curable sexually transmitted infections - 2008. 2012. Available from:http://apps.who.int/iris/bitstream/10665/75181/1/9789241503839_eng.pdf [Last accessed on 2013 May 17].
5.	Stamm WE, Jones RB, Batteiger BE. Part III. Infectious Diseases and their etiologic agents, Section C. Chlamydial Diseases. In: Mandell GL, Bennett JE, Dolin R, editors. Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases. Philadelphia: Churchill Livingston; 2005.
6.	Anttila T, Saikku P, Koskela P, Bloigu A, Dillner J, Ikäheimo I, et al. Serotypes of Chlamydia trachomatis and risk for development of cervical squamous cell carcinoma. JAMA 2001;285:47-51.
7.	Galvin SR, Cohen MS. The role of sexually transmitted diseases in HIV transmission. Nat Rev Microbiol 2004;2:33-42.
8.	Madeleine M, Anttila T, Schwartz S, Saikku P, Leinonen M, Carter JJ, et al. Risk of cervical cancer associated with Chlamydia trachomatis antibodies by histology, HPV type and HPV cofactors. Int J Cancer 2007;120:650-5.
9.	Bhalla P, Baveja UK, Chawla R, Saini S, Khaki P, Bhalla K, et al. Simultaneous detection of Neisseria gonorrhoeae and Chlamydia trachomatis by PCR in genitourinary specimens from men and women attending an STD clinic. J Commun Dis 2007;39:1-6.
10.	Chen XS, Yin YP, Mabey DR, Peeling W, Zhou H, Jiang WH, et al. Prevalence of Chlamydia trachomatis infections among women from different settings in China: Implications for STD surveillance. Sex Transm Infect 2006;82:283-4.
11.	Zhang JJ, Zhao GL, Wang F, Hong FC, Luo ZZ, Lan LN, et al. Molecular epidemiology of genital Chlamydia trachomatis infection in Shenzhen, China. Sex Transm Infect 2012;88:272-7.
12.	Chen KT, Chen SC, Chiang CC, Li LH, Tang LH. Chlamydial infection among patients attending STD and genitourinary clinics in Taiwan. BMC Public Health 2007;7:120.
13.	Garland SM, Tabrizi SN, Chen S, Chen S, Byambaa C, Davaajav K. Prevalence of sexually transmitted infections (Neisseria gonorrhoeae, Chlamydia trachomatis, Trichomonas vaginalis and human papillomavirus) in female attendees of a sexually transmitted diseases clinic in Ulaanbaatar, Mongolia. Infect Dis Obstet Gynecol 2001;9:143-6.
14.	Falk L, Fredlund H, Jensen JS. Signs and symptoms of urethritis and cervicitis among women with or without Mycoplasma genitalium or Chlamydia trachomatis infection. Sex Transm Infect 2005;81:73-8.
15.	Berg A. Screening for chlamydial infection: Recommendations and rationale. Am J Prev Med 2001;20(3 Suppl):90-4.
16.	Reported STI Data from National STD/AIDS Control Programme - End 2012. [National STD/AIDS control program website]. 2010-2012. Available from:http://www.aidscontrol.gov.lk/web/index.php?option=com_contentandview=articleandid=38andItemid=52andlang=en. [Last accessed on 2013 May 27].
17.	Araújo RS, Guimarães EM, Alves MF, Sakurai E, Domingos LT, Fioravante FC, et al. Prevalence and risk factors for Chlamydia trachomatis infection in adolescent females and young women in central Brazil. Eur J Clin Microbiol Infect Dis 2006;25:397-400.
18.	Al-soud WA, Radstrom P. Purification and characterization of PCR-inhibitory components in blood cells, J Clin Microbiol 2001;39:485-93.
19.	Black CM, Marrazzo J, Johnson RE, Hook III EW, Jones RB, Green TA, et al. Head-to-Head multicenter comparison of DNA probe and nucleic acid amplification tests for Chlamydia trachomatis infection in women performed with an improved reference standard. J Clin Microbiol 2002;3757-63.
20.	Ramachandran S, Ngeow YF. The prevalence of sexually transmitted diseases among prostitutes in Malaysia. Genitourin Med 1990;66:334-6.
21.	León SR, Konda KA, Klausner JD, Jones FR, Cáceres CF, Coates TJ, et al. Chlamydia trachomatis infection and associated risk factors in a low-income marginalized urban population in coastal Peru. Pan Am J Public Health 2009;26:39-45.
22.	Thuong NV, Long NT, Hung ND, Truc LT, Nhung VT, Van CT, et al. Sexually transmitted infections in female sex workers in five border provinces of Vietnam. Sex Transm Dis 2005;32:550-6.
23.	Latino MA, Bello L, Lanza A, Leotta E, Tersiev P, De Intinis G, et al. Chlamydia trachomatis infection among sexually active young women in Italy. Sex Transm Infect 2002;78:e4.
24.	Domeika M, Butylkina R, Hallén A, Spukaite T, Juceviciute V, Morkunaite D, et al. Prevalence of Chlamydia trachomatis infections in women attending six women's healthcare units in Kaunas, Lithuania. Sex Transm Infect 2001;77:459-60.
25.	Christian P, Khatry SK, LeClerq SC, Roess AA, Wu L, Yuenger JD, et al. Prevalence and risk factors of chlamydia and gonorrhea among rural Nepali women. Sex Transm Infect 2005;81:254-8.
26.	Paris M, Gotuzzo E, Goyzueta G, Aramburu J, Caceres CF, Castellano T, et al. Prevalence of gonococcal and chlamydial infections in commercial sex workers in a Peruvian Amazon city. Sex Transm Dis 1999;26:103-7.
27.	Nguyen TV, Khuu NV, Le TT, Nguyen AP, Cao V, Tham DC, et al. Sexually transmitted infections and risk factors for gonorrhea and chlamydia in female sex workers in Soc Trang, Vietnam. Sex Transm Dis 2008;35:935-40.
28.	Cwikel JG, Lazer T, Press F, Lazer S. Sexually transmissible infections among female sex workers: An international review with an emphasis on hard-to-access populations. Sex Health 2008;5:9-16.
29.	Samarakoon S, Thayaparan P, Sivayogam S. Condom use among female sex workers in Colombo Sri Lanka. Presented at: International Conference on AIDS [ThPeC7412]; 2004. p.15.