Objective: We conducted a survey to compare condom use and its associated factors between foreign Asian and local clients of female sex workers in Singapore.
Study: A survey was conducted between 2001 and 2002 on a random sample of 810 clients (677 foreign Asian workers and 133 locals) recruited from the streets and outside the brothels in Singapore.
Results: Foreign clients were more likely than locals to be inconsistent condom users with sex workers. Clients from China reported the highest percentage of inconsistent condom use (29.2%) and sexually transmitted infections (16.7%) compared with 8.3% (P < 0.003) and 2.3% (P < 0.005), respectively, among locals. On multivariate analysis, inconsistent condom use among foreign clients increased significantly with the number of freelance sex workers. The reverse trend was found for local clients.
Conclusion: There is a need to design separate condom-promotion programs for foreign Asian and local clients of sex workers in Singapore.
A survey of clients of female sex workers in Singapore found that inconsistent condom use and self-reported sexually transmitted infections were significantly higher among foreign Asian than local clients.
From the *Department of Community, Occupational and Family Medicine Faculty of Medicine, National University of Singapore; †Department of STD Control, National Skin Center, Ministry of Health, Singapore; and the ‡Epidemiology and Disease Control Unit, Ministry of Health, Singapore
The authors thank Ms Chew Keng Lee for coordinating the project and all our student interviewers for their hard work and courage in conducting the interviews in the red-light areas in Singapore.
Correspondence: Wong Mee Lian, MPH, MD, Associate Professor, Department of Community, Occupational and Family Medicine (MD 3), Faculty of Medicine, National University of Singapore, 16, Medical Drive, Singapore 117597. E-mail: firstname.lastname@example.org.
This research was funded by a research grant (R 186–000-047–213) from the National Medical Research Council, Singapore.
IN MANY ASIAN1–3 AND other countries in the developing world,4 the main mode of human immunodeficiency virus (HIV) transmission is male patronage of female commercial sex workers. Surveys in Asia showed that between 10%5 and 86%6,7 of adult men have visited a female sex worker in a given year. Male clients of sex workers are not only at risk of contracting sexually transmitted infections (STIs) and HIV but they act as a “bridge” for transmitting the infections to and from female sex workers to other sex partners, including their wives.8–10
Most STI/HIV control programs have targeted female sex workers, with some succeeding in increasing condom use and reducing STI/HIV incidence among them.11–17 However, success may be limited because sex workers often do not have full control over condom use.18,19 Condom promotion and STI/HIV interventions should target male clients of female sex workers as well. These clients are very varied, comprising locals, migrant workers, tourists, and illegal immigrants. Presently, STI/HIV prevention intervention programs for clients of female sex workers are few and are mostly targeted at locals,16,20,21 tourists,22 or whites working abroad.23,24 There are no programs targeting the large and growing number of male foreign workers who come from Asian countries with high STI and HIV prevalence1,25,26 such as India, China, Myanmar, Indonesia, and Thailand to work for a few years in higher-income Asian countries like Japan, Hong Kong, Malaysia, and Singapore. Little is known about their sexual behavior. Although research on clients of sex workers in Asia has been carried out among local population groups,27,28 truck drivers,29,30 tourists,31 and migrant workers,32 no study has examined the sexual behavior of the growing group of temporary foreign Asian workers who patronize sex workers in their new country of work in Asia.
In Singapore, there are about 250,000 male foreign workers, constituting nearly 6.5% of the population. Most of the foreign unskilled workers in Singapore are from Malaysia, Thailand, China, Bangladesh, and India.33 Very little is known about the sexual behavior of these male foreign Asian workers. They may patronize female sex workers owing to their long absence from their families, and peer influence in their new work environment. Do their sexual behaviors differ from local clients? We conducted this study to compare condom use and its associated factors between foreign Asian and local clients of female sex workers in Singapore. The findings would help plan relevant and culturally appropriate STI/HIV interventions for these foreign workers
Study Population and Sample
A cross-sectional study was conducted from September 2001 to December 2002 on foreign Asian and local clients who patronized freelance or brothel-based sex workers in the eastern and central part of Singapore, where all geographically designated areas for brothels are situated. A client in our study was defined as a local male Singaporean or a foreign Asian who worked in Singapore during the period of the survey and had paid sexual intercourse with a female sex worker in the past 6 months.
The estimated number of registered brothel-based sex workers in Singapore in 2002 is 1000. Based on a mean of 10 clients per day per brothel-based sex worker from our earlier study,34 the number of clients visiting brothel-based sex workers is estimated to be 10,000 per day. From our reconnaissance of the freelance sex workers, we estimated their total number to be at least twice that of brothel-based sex workers. Our earlier study on freelance sex workers35 found that the majority (92%) reported only about half of the number of clients seen per day by brothel-based sex workers. Hence, we estimated a total of at least 20,000 clients per day with approximately equal numbers each (n = 10,000) patronizing brothel-based or freelance sex workers.
We conducted a weeklong presurvey reconnaissance to observe the volume and sociodemographic characteristics of clients patronizing sex workers in the study area, followed by a pilot study on 50 clients there to determine the sample size and the main ethnic distribution of the Asian clients. Based on this study, which found a prevalence of consistent condom users of 80% among the clients and a predominance and almost equal distribution of Bangladeshis, Indonesians, Thais, and Chinese (local and nonlocals), we estimated that a sample size of at least 800 clients was required to provide at least 100 inconsistent condom users and sufficient numbers of at least 200 clients in each ethnic group for meaningful analysis. After factoring a 20% nonresponse rate, a sample of 1000 clients has to be recruited with 500 selected from clients visiting brothels and 500 from those patronizing freelance sex workers.
As it is very difficult to obtain a sampling frame and get a truly representative sample of this ill-defined and mobile client population, a 2-stage sampling strategy was used. First, a sampling frame of rent-a-room hotels from which freelance sex workers operated was mapped out from the presurvey reconnaissance, while the sampling frame of brothels (n = 85) was obtained from the Department of STI Control. From these 2 sampling frames, 50 rent-a-room hotels and 50 brothels were randomly selected for the study for logistic reasons. Next, 10 clients from each of these sites were selected by systematic sampling as they stepped out from the brothels or rent-a-room hotels.
Interviewers waited outside the randomly selected brothels and rent-a-room hotels during the sex workers’ operating hours from 1900 hours to 0200 hours on all days of the week during the period of the survey and requested interviews from clients who came out from these places. The short questionnaire included sociodemographic items such as nationality, marital status, age, occupation, and educational level. Respondents were also asked on the number of sexual encounters, types of sex worker (freelance or brothel-based) visited, and condom use with them in the past 6 months and for the most recent encounter. In addition, they were asked whether they had experienced any STI symptoms such as genital discharge, ulcer or sore, genital growth, and painful urination and on their treatment-seeking behavior in the past 6 months.
We attempted to reduce self-reporting bias on condom use by taking the following measures. First, we engaged university student-interviewers of similar nationalities as our clients so that they could speak their language and be trusted by them. Students were also perceived to be less threatening than official staff. Second, the interviewers assured them about confidentiality and stressed the importance of honest answers to help plan better programs to protect them from STIs and AIDS. Last, we facilitated accurate recall by interviewing clients on condom use during their most recent sexual encounter with the sex worker, when they have just come out from the brothels or rent-a-room hotels. However, as the most recent episode might not represent the usual behavioral pattern of the clients, we also asked them about condom use for all sexual acts with the sex workers in the past 6 months. The majority (62%) had 2 sexual acts with the sex workers in the past 6 months; we facilitated their recall on condom use by getting them to work backwards from the most recent encounter. Interviewers were trained on how to approach clients and put them at ease by starting with informal conversations. The interviewers first explained that they were university students doing a lifestyle survey. After getting verbal informed consent, the interviewers directed nonsensitive questions at the clients such as their lifestyles pertaining to their travel, diet, and smoking before proceeding to questions on sexual behavior. A total of 1080 clients were approached, of which 810 (75%) agreed to participate in the survey.
An inconsistent condom user was defined as a client who did not use a condom for at least 1 of the acts of vaginal intercourse with the sex workers in the past 6 months. Brothel-based sex workers were defined as those who worked from brothels regulated under the Medical Surveillance Scheme, which requires all sex workers to attend regular screening for STIs and HIV at designated clinics. Freelance sex workers included sex workers who solicited clients from the streets, bars, nightclubs, or massage parlors.
Inconsistent condom use was compared between foreign and local clients in relation to nationality, occupation, age, marital status, educational level, type of sex worker, and other variables. χ2 Test was used to compare proportions in condom use for categorical variables and t test for continuous variables such as age.
Multiple logistic regression models were fitted, using univariate variables with P < 0.1 as inputs to identify predictors of inconsistent condom use and self-reported STIs. All independent socio-demographic and behavioral variables with a level of statistical significance of 0.1 or less in univariate analysis were entered stepwise into logistic regression models with inconsistent condom use as the dependent dichotomous variable (yes versus no). This multivariate statistical analysis yielded the adjusted odds ratios of inconsistent condom use by independent variables, simultaneously adjusted for socio-demographic variables. The Statistical Package for Social Science (SPSS), version 11.0 (SPSS, Chicago, IL) was used for data analysis. The level of significance was set at 0.05.
Only 133 (16.4%) of the clients were locals. The majority (83.6%) were foreigners with about one quarter each being Indonesians, Bangladeshis, or Thais, and the last quarter comprising Chinese nationals, Malaysians, and Indian nationals. Less than 3% visited the same sex worker more than once.
Table 2 compares the sociodemographic characteristics of foreign and local clients. There were significantly fewer professionals and more unskilled workers such as laborers and construction workers among foreign clients. Foreign clients were also less educated and younger than local clients. The 2 groups did not differ in the number of sex workers patronized in the past 6 months. However, a significantly higher proportion of foreign clients patronized freelance sex workers compared to local clients (65.2% versus 47.3%, P < 0.001).
Condom Use in the Past 6 Months and for the Most Recent Encounter With Sex Workers
The overall prevalence of condom use was 87.3%. A consistent, though not statistically significant, pattern was observed, with a higher proportion of inconsistent condom users among foreign Asian than local clients in the last 6 months (12.4% versus 8.3%, P = 0.159) and for the most recent encounter (3.1% versus 1.5%, P = 0.274). On stratifying by nationality, the highest proportion of inconsistent condom users in the past 6 months was reported among clients from China (29.2%), followed by Bangladeshis (15.5%), Thais (10.6%), and Indonesians (9.0%), with the lowest proportion among local clients (8.3%). The difference in inconsistent condom use between Chinese nationals and local clients was statistically significant for the last 6 months and for the most recent encounter (29.2% versus 8.3%, P < 0.005; 12.5% versus 1.5%, P < 0.05). Similar statistically significantly differences were found between Bangladeshis and locals (15.5% versus 8.3%, P < 0.05).
We also examined whether condom use was initiated by the client or the sex worker. A significantly lower proportion of foreign than local clients initiated condom use for the most recent encounter (11% versus 26%, P < 0.05). For all sexual contacts and regardless of the clients’ nationality, sex workers were significantly more likely than clients to initiate condom use.
Inconsistent Condom Use by Sociodemographic Characteristics of Foreign and Local Clients
Table 2 compares inconsistent condom use in the past 6 months and for the most recent encounter between foreign and local clients by sociodemographic characteristics and the type and number of sex workers patronized. For both client groups, professionals, businessmen, and managers reported the highest percentage of inconsistent condom use compared with other occupations. Inconsistent condom use did not differ by marital status or age. There were significantly higher percentages of inconsistent condom users in the past 6 months among higher- than lower-educated foreign clients, but no association was found for local clients.
Significant differences in inconsistent condom use were also observed between foreign and local clients with regard to the type of sex worker patronized. For foreign clients, inconsistent condom use in the past 6 months increased significantly with the number of sexual contacts with freelance sex workers, reaching 21.9%, when the number increased to 3 and more. This pattern contrasted with local clients in which inconsistent condom use decreased with higher number of contacts with freelance sex workers. Inconsistent condom use was not significantly associated with the number of brothel-based sex workers patronized among both foreign and local clients.
With regard to the most recent encounter with the sex worker, noncondom use varied significantly with the type of sex worker among foreign clients; those who had sexual contact with freelance sex workers were significantly more likely than those with sexual contact with brothel-based sex workers to be nonusers of condoms. Noncondom use was not associated with sociodemographic characteristics of the clients (not shown in the table).
Multivariate Analysis of Predictors of Inconsistent Condom Use
Two separate multivariate logistic regression analyses were conducted to determine independent factors significantly associated with (i) inconsistent condom use in the past 6 months and (ii) noncondom use for the most recent encounter (Table 3). Inconsistent condom use among foreign clients showed a marginally significant association with educational level, with higher-educated clients being more likely to be inconsistent condom users. Having sexual contact with freelance sex workers was the only variable that showed a significant independent association with inconsistent condom use both for the past 6 months and the most recent encounter. A dose-response relationship was seen with an increasing trend in inconsistent condom use with an increasing number of contacts with freelance sex workers. Clients with 3 or more sexual contacts with freelance sex workers were about 5 times more likely to be inconsistent condom users compared to those who did not patronize freelance sex workers at all. For local clients, none of the variables were significantly associated with inconsistent condom use (not shown in the table).
Foreign clients reported a slightly higher but not statistically significant prevalence of STIs in the past 6 months than local clients (3.2% versus 2.3%, P = 0.283). The symptoms commonly reported by foreign clients were pain on urination (2.7%), followed by genital ulcer (0.7%) and genital growth (0.1%). Self-reported STIs were analyzed by sociodemographic characteristics and condom use among foreign clients only (Table 4) as the numbers among locals were too small for meaningful analysis. STIs were significantly associated with nationality of clients, with clients from China reporting a significantly much higher percentage (16.7%) compared to other nationalities (<5%). Self-reported STIs were also significantly associated with frequency of unprotected sexual exposures with sex workers. In the multiple logistic regression analysis, the number of unprotected sexual exposures with sex workers was the only factor significantly associated with self-reported STIs (adjusted odds ratio: 13.7, 95% CI, 4.66–40.33).
Of those 25 clients who self-reported STIs, only 44% sought treatment from clinics and hospitals, where all of them were confirmed by laboratory tests. The others self-medicated (24%), got medicine from friends (24%), or sought treatment from traditional practitioners (8%). A higher proportion of foreign clients than locals self-medicated or obtained medicine from friends (57.4% versus 33.3%). Only 13.6% of foreign clients compared with 66.7% of locals sought treatment within 1 week of symptom onset.
This is, to our knowledge, the first study that examined condom use among local and foreign Asian worker clients of sex workers in an Asian country. Foreign clients were more likely to be inconsistent condom users and to patronize freelance sex workers. Inconsistent condom use among them increased with higher number of sexual contacts with freelance sex workers but not with brothel-based sex workers.
The high level of condom use (>88%) among the overall sample of foreign Asian and local clients, which was quite similar to that in the United States,36 United Kingdom,37,38 Holland,39 Ghana,4 Peru,40 and Thailand16 but much higher than that reported from Hong Kong,27 Indonesia,28 and Bangladesh,30 may be attributed to the 100% condom promotion programs that have been implemented for brothel-based sex workers in Singapore since 1995.17
It is unclear why foreign but not local clients showed an increase in inconsistent condom use with higher frequency of sexual contacts with freelance sex workers. Other researchers also found that inconsistent condom users reported more contacts with sex workers40 and have explained it as follows. First, clients trusted the sex worker who would often be a regular partner. Second, clients had a high level of sexual desire and a desire for variation.41 In view of this unexpected finding, the first author conducted some preliminary in-depth interviews with 10 foreign clients of different nationalities who did not use condoms with freelance sex workers. All of them reported that they did not think about using condoms or the risk of getting HIV/STI when they were out to “enjoy” themselves. In contrast, the decrease in inconsistent condom use with higher number of freelance sex workers patronized among local clients may be explained by their greater awareness of the higher level of STIs among freelance sex workers, who do not attend regular STI screening like brothel-based sex workers. Foreign clients may not have been exposed to this information. Further qualitative research is needed to improve our understanding of this difference in condom use between foreign and local clients.
Our finding on the increase in inconsistent condom use with higher educational level among foreign clients contrasted with most studies.27,28,31 As sex workers were more likely than their clients to initiate condom use in our study, the lower condom use rate among better-educated clients may be explained by the increased difficulty sex workers found in persuading higher-educated compared to lower-educated clients to use condoms. This needs to be confirmed by further research.
This study has some limitations. First, we were unable to compare the sociodemographic characteristics between participants and nonparticipants as the majority did not want to talk at all to our interviewers. It was difficult too to distinguish them by nationality because of their similarity in appearance. For example, some local Chinese looked the same as Chinese nationals. Second, we were not able to carry out a more comprehensive study of knowledge, psychological and behavioral factors with condom use because of logistical constraints and sensitivities associated with interviewing clients in the red-light areas. The majority felt uncomfortable about being held up for an interview and wanted to rush off. This study has now been expanded to include some of the abovementioned factors among clients attending the public STI clinic. Another limitation is that clients might overreport condom use. We took steps to reduce false reporting and facilitate accurate recall. To date, there is no acceptable “gold standard” to validate self-reports of condom use. However, there appears to be reasonable evidence for the validity of self-reports on condom use if measures are taken to reduce self-reporting bias.42 It should be noted that the primary goal of this exploratory study is to compare patterns of condom use between local and foreign clients. If there is overreporting, it is likely to occur across all groups. Self-reported STIs also have their biases. However, it is not feasible to confirm STIs by diagnostic tests in a community-based survey on such an ill-defined and mobile population of foreign Asian clients. The primary aim of asking about STIs in this study is not to determine the actual prevalence of STIs but to find out the percentage of those with self-reported STIs who sought treatment. The strength of this study, however, is that this big sample of clients was recruited directly from the brothels and the streets.
In conclusion, condom use with sex workers differed between local and foreign Asian clients, with the latter being less likely to use condoms consistently. Our data suggest that foreign clients are at higher risk than local clients of acquiring and spreading STI/HIV due to their higher inconsistent condom use and STI rates and their increased likelihood of patronizing freelance sex workers who were at higher risk of contracting STIs.35 There is a clear need to prioritize and design separate condom promotion programs for foreign Asian clients of sex workers in Singapore.
1. Ruxrungtham K, Brown T, Phanuphak P. HIV/AIDS in Asia: review. Lancet 2004; 364:69–82.
2. Hanenberg RS, Rojanapithayakorn W, Kunasol P, Sokal DC. Impact of Thailand’s HIV control program as indicated by the decline of sexually transmitted diseases. Lancet 1994; 344:243–245.
3. Sirisopana N, Torugsa K, Mason CJ, et al.. Correlates of HIV-1 seropositivity among young men in Thailand. J Acquir Immun Defic Syndr Hum Retrovirol 1996; 11:492–498.
4. Cote AM, Sobela F, Dzokoto A, et al.. Transactional sex is the driving force in the dynamics of HIV in Accra, Ghana. AIDS 2004; 18:917–925.
5. Heng BH, Lee HP, Kok LP, Ong YW, Ho ML. A survey of sexual behavior of Singaporeans. Ann Acad Med Singapore 1992; 21:723–729.
6. Sopheab H, Phalla T, Leng HB, Wantha SS, Gorbach PM. Cambodian Household Male Survey (BSSIV 2000) Phnom Penh: National Center for HIV/AIDS, Dermatology, and Sexually Transmitted Diseases Ministry of Health: 2001 July Report
7. Nopkesorn T, Mastro TD, Sangkharomya S, et al.. HIV-infection in young men in northern Thailand. AIDS 1993; 7:1233–1239.
8. Lau JT, Thomas J. Risk behaviours of Hong Kong male residents traveling to mainland China: a potential bridge population for HIV infection. AIDS Care 2001; 13:71–81.
9. Morris M, Podhisita C, Wawer JM, Haddock MS. Bridge population in the spread of HIV/AIDS in Thailand. AIDS 1996; 10:1265–1271.
10. Gorbach PM, Sopheab H, Phalla T, et al.. Sexual bridging by Cambodian men: potential importance for general population spread of STD and HIV epidemics. Sex Transm Dis 2000; 27:320–326.
11. Laga M, Alary M, Nzilambi N, et al.. Condom promotion, sexually transmitted diseases treatment, and declining incidence of HIV-1 infection in female Zairian sex workers. Lancet 1994; 344:246–248.
12. Ngugi EN, Plummer FA, Simonsen JN, et al.. Prevention of transmission of human immunodeficiency virus in Africa: effectiveness of condom promotion and health education among prostitutes. Lancet 1988; 2:887–889.
13. Ngugi EN, Wilson D, Sebstad J, Plummer FA, Moses S. Focused peer-mediated educational programs among female sex workers to reduce sexually transmitted disease and human immunodeficiency virus transmission in Kenya and Zimbabwe. J Infect Dis 1996; 174:S240–247.
14. Ghys PD, Diallo MO, Ettiegne-Traore V, et al.. Increase in condom use and decline in HIV and sexually transmitted diseases among female sex workers in Abidjan, Cote d’lvoire, 1991–1998. AIDS 2002; 16:251–258.
15. Alary M, Mukenge-Tshibaka L, Bernier F, et al.. Decline in the prevalence of HIV and sexually transmitted diseases among female sex workers in Cotonou, Benin, 1993–1999. AIDS 2002; 16:463–470.
16. Rojanapithayakorn W, Hanenberg R. The 100% condom program in Thailand. AIDS 1996; 10:1–7.
17. Wong ML, Chan Roy KW, Koh D. The long term effects of condom promotion programmes for vaginal and oral sex on sexually transmitted infections among sex workers in Singapore, 1990–2002. AIDS 2004; 18:1195–1199.
18. Thuy NT, Nhung VT, Thuc NV, Lien TX, Khiem HB. HIV infection and risk factors among female sex workers in Southern Vietnam. AIDS 1998; 12:425–432.
19. Ford K, Wirawan DN, Reed BD, Muliawan P, Wolfe R. The Bali STD/AIDS Study: evaluation of an intervention for sex workers. Sex Transm Dis 2002; 29:50–58.
20. Lowndes CM, Alary M, Gnintoungbe CA, et al.. Management of sexually transmitted diseases and HIV prevention in men at high risk: targeting clients and non-paying sexual partners of female sex workers in Benin. AIDS 2000; 14:2523–2524.
21. Wilson D, Chiroro P, Lavelle S, Mutero C. Sex worker, client sex behaviour and condom use in Harare, Zimbabwe. AIDS Care 1989; 1:269–280.
22. Centers for Disease Control and prevention. Health Information for the International Traveler, 2001–2002
. Atlanta: US Department of Health and Human Services, Public Health Service, 2001.
23. Matteelli A, Carosi G. Sexually transmitted diseases in travelers. Clin Infect Dis 2001; 32:1063–1067.
24. Hopperus Buma AP, Veltink RL, van Ameijden EJ, Tendeloo CH, Coutinho RA. Sexual behaviour and sexually transmitted diseases in Dutch marines and naval personnel on a United Nations mission in Cambodia. Genitourin Med 1995; 1:172–175.
25. Joint United Nations Program on HIV/AIDS (UNAIDS) and World Health Organization (WHO). AIDS Epidemic Update: December 2001
. Geneva: UNAIDS/WHO, 2001. WHO/CDS/CSR/NCS/2001.2.
26. The World Health Organization. Global Prevalence and Incidence of Sexually Transmitted Infections: Overview and Estimates
. Geneva: Department of Communicable Disease Surveillance and Response, 2001. Nov. Report WHO/CDS/CSR/EDC/2001.10.
27. Lau JT, Tsui HY. Behavioral surveillance surveys of the male clients of female sex workers in Hong Kong: results of three population-based surveys. Sex Transm Dis 2003; 30:620–628.
28. Ford K, Wirawan DN, Muliawan P. Social influence, AIDS/STD knowledge, and condom use among male clients of female sex workers in Bali. AIDS Educ Prev 2002; 14:496–504.
29. Manjunath JV, Thappa DM, Jaisankar TJ. Sexually transmitted diseases and sexual lifestyles of long-distance truck drivers: A clinico-epidemiologic study in south India. Int J STD AIDS 2002; 13:612–617.
30. Gibney L, Saquib N, Metzger J. Behavioral risk factors for STD/HIV transmission in Bangladesh’s trucking industry. Social Sci Med 2003; 56:1411–1424.
31. Lau JTF, Tang ASY, Tsui HY. The relationship between condom use, sexually transmitted diseases, and location of commercial sex transaction among male Hong Kong clients. AIDS 2003; 17:105–112.
32. Mullany LC, Maung C, Beyrer C. HIV/AIDS knowledge, attitudes, and practices among Burmese migrant factory workers in Tak Province, Thailand. AIDS Care 2003; 15:63–70.
33. Foreign Workers in Singapore: Migration News
. San Francisco: German Marshall Fund of the United States and the University of California-Berkeley Center for German and European Studies, 1996; 3:12.
34. Wong ML, Chan RKW, Koh D. Promoting condom use for oral sex: its impact on pharyngeal gonorrhoea among female brothel-based sex workers. Sex Transm Dis 2002; 29:311–318.
35. Wong ML, Chan RKW, Chua WL, Wee S. Sexually transmitted diseases and condom use among free-lance and brothel-based sex workers in Singapore. Sex Transm Dis 1999; 26:593–600.
36. Albert AE, Warner DL, Hatcher RA. Facilitating condom use with clients during commercial sex in Nevada’s legal brothels. Am J Public Health 1998; 88:643–646.
37. Day S, Ward H, Perrotta L. Prostitution and risk of HIV: male partners of female prostitutes. BMJ 1993; 307:359–361.
38. Barnard M, McKeganey NP, Leyland AH. Risk behaviours among male clients of female prostitutes. BMJ 1993; 307:361–362.
39. Graaf R de, Zessen IV, Straver CJ, Visser JH. Condom use by Dutch men with commercial heterosexual contacts: determinants and considerations. AIDS Educ Prev 1997; 9:411–423.
40. Miller GA, Mendoza W, Krone MR, et al.. Clients of female sex workers in Lima, Peru: a bridge population for sexually transmitted disease/HIV transmission? Sex Transm Dis 2004; 31:337–342.
41. Vanwesenbeeck I, de Graaf R, Van Zessen G, Straver CJ, Visser JH. Protection styles of prostitutes’ clients: intentions, behavior and considerations in relation to AIDS. J Sex Educ Ther 1993; 19:79–92.
© Copyright 2005 American Sexually Transmitted Diseases Association
42. Fishbein M, Pequegnat W. Evaluating AIDS prevention interventions using behavioral and biological outcome measures. Sex Transm Dis 2000; 27:101–110.