International Journal of Infectious Diseases (2007) 11, 115—122 http://intl.elsevierhealth.com/journals/ijid Sexually transmitted Chlamydia trachomatis, Neisseria gonorrhoeae, and HIV-1 infections in two at-risk populations in Barcelona: female street prostitutes and STI clinic attendees M. Vall-Mayans a,*, M. Villa b, M. Saravanya a, E. Loureiro a, M. Meroño c, E. Arellano a, B. Sanz a, P. Saladié a, A. Andreu b, M.G. Codina b a Sexually Transmitted Infections Unit, Primary Health Center Drassanes, Catalan Health Institute, E-08001 Barcelona, Spain Microbiology and Parasitology Service, Hospital Vall d’Hebron, Catalan Health Institute, Barcelona, Spain c Àmbit Dona, Àmbit Prevenció, Barcelona, Spain b Received 17 May 2005; received in revised form 28 October 2005; accepted 15 November 2005 Corresponding Editor: Salim S. Abdool Karim, Durban, South Africa KEYWORDS Chlamydia trachomatis; Neisseria gonorrhoeae; HIV-1; Prostitution; STI clinic Summary Objective: To determine the prevalence of Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG), and HIV-1 infections in female street prostitutes and STI clinic attendees in Barcelona. Design: This was a prospective study carried out in two four-month periods over two years. Urine specimens were tested for CTand NG using a PCR pooling algorithm. Among street prostitutes HIV1 testing in urine was also carried out. Results: The prevalences of CT, NG, and HIV-1 in female street prostitutes (n = 301) were 4.7%, 3.7%, and 1.0%, respectively. Women from Eastern Europe had the highest prevalence of CT ( p = 0.01). Prevalences of CT, NG, and HIV-1 among all clinic attendees (n = 536) were 4.3%, 4.5%, and 4.4%, respectively. Prevalence of HIV-1 infection among homosexual men was higher compared with heterosexual men and women ( p < 0.001). Conclusions: : Overall CT prevalence is currently lower than in other European countries, although it could increase as a result of immigration. Rates of HIV-1 and of NG are higher among homosexual than among heterosexual men. # 2006 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. Introduction * Corresponding author. Tel.: +34 93 441 4612; fax: +34 93 441 4612. E-mail address: mvall.pbcn@ics.scs.es (M. Vall-Mayans). Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are two of the most common sexually transmissible infective agents. It is well recognized throughout the world that both 1201-9712/$32.00 # 2006 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijid.2005.11.005 116 M. Vall-Mayans et al. Methods detailing the study to participants. After giving their informed consent, sex workers were invited to answer a structured questionnaire that was completed by a female health professional hired for the project. They were also invited to submit a urine specimen while at the Àmbit Dona for NG, CT, and HIV-1 testing. Those participating in the study were invited to attend the STI unit of the Catalan Health Institute, Barcelona for further STI check ups. In addition, participants with a positive result for NG or CTwere provided free oral treatment on site according to recommended guidelines.9 The HIV-1 test results from this population were used only for epidemiological purposes. A few male street prostitutes who had also requested the services of the outreach organization while the study was ongoing were also asked to participate. As male street prostitutes were not the target study population and selection bias could not be ruled out, only urine STI prevalence results are given for this specific population. (b) The participants at the STI unit of the Catalan Health Institute, Barcelona included mainly self-referred asymptomatic subjects requesting HIV testing and, to a lesser extent, STI symptomatic patients (15%) and non-street prostitutes (25%). All were given a leaflet in a relevant language about the study before consultation, and after being informed about the project by a nurse or physician and giving their informed consent, they were asked to submit a urine specimen for NG and CT testing. This study population was not asked to answer a questionnaire since information was retrieved from clinical records by the health professional hired for the project under the supervision of the principal investigator of the study who belonged to the clinic. Each subject was asked to participate in the study once at his/her visit to the clinic. As usual, treatment, additional testing, and contact tracing were offered in the clinic following recommended guidelines.9 HIV status from the STI unit attendees was obtained on the same day as HIV testing was requested or consented to. Details concerning seroprevalence of HIV from the STI unit of the Catalan Health Institute, Barcelona have been published eleswhere.7 This study was approved by the ethical and scientific committees of the Primary Health Care Division of the Catalan Health Institute (Fundació Jordi Gol i Gurina per a la Recerca a l’Atenció Primària). Study sites and populations Specimen collection, transport, and processing Between February and June 2002 and again in 2003, firstcatch urine specimens were collected from consecutively enrolled study participants in the two selected populations: (a) female street prostitutes and (b) STI clinic attendees. With a 95% confidence interval and a power of 80%, a sample size of 200 female street prostitutes was required to estimate a prevalence of NG or CTaround 5% with a precision of 3%, and a sample size of 800 STI clinic attendees to estimate a prevalence of NG or CT around 2% with a precision of 1%. (a) Female street prostitutes in the Ciutat Vella old district of Barcelona, a popular location for prostitution, were approached after contacting a well-respected Catalan outreach organization, Àmbit Prevenció, with a specific service for female prostitutes, Àmbit Dona (i.e., women’s site). Outreach workers informed the women about the project and handed out a leaflet (produced in different languages) First-void urine specimens were collected in a sterile container and were shipped to the laboratory at 4 8C. They were stored at 2—8 8C for up to seven days or at 20 8C until they were processed. Pools of four specimens were prepared each by mixing 400 mL of urine.10 Specimen processing was undertaken following the manufacturer’s instructions for the urine-based CT/NG PCR (Cobas Amplicor, Roche Diagnostics, Branchburg, NJ, USA). Specimens yielding CT or NG signals above the test cutoff were interpreted as positive regardless of the internal control result. If these signals were negative and the internal control was above the cutoff value, the sample was considered negative. Specimens with signals below the cutoffs for CT, NG, and internal control, were interpreted as inhibitory. Positive pools or pools with inhibitory activity were retested individually. of them cause sexually transmitted diseases and affect the reproductive tract with grave sequelae.1 The prevalence of infection attributable to each of these organisms varies geographically and according to the population studied: broadly speaking CT is more prevalent than NG in industrialized countries and the reverse in developing countries, and both of them are more prevalent among people at high risk of sexually transmitted infections (STIs). Many studies have documented high rates of CT in parts of Europe2 and North America3 affecting young people, both heterosexual and homosexual men, and especially women. The burden of CT and NG in Catalonia and Spain is largely unknown due to the scarcity of data. Taking into consideration the fact that the few studies undertaken have been limited to symptomatic patients in some STI centers or other populations at lower risk, using generally insensitive testing methods, the prevalence of CT in Catalonia and Spain still appears to be lower than that in other parts of Europe.4 Similar to other cities in industrialized countries, since the late 1990s there has been a progressive increase in the number of NG cases diagnosed in Barcelona, affecting homosexual men in particular.5 HIV infection is the STI with the highest impact worldwide and it has consistently been shown to be associated with other STIs.6 The overall HIV epidemic in Spain is concentrated, with relatively low prevalence among all heterosexuals, including female prostitutes, but with much higher prevalence among subpopulations of homo/bisexual men and immigrants.7,8 Globalization has had an impact on sex-related issues such as prostitution and international travel to specific sites to engage in sexual activities (homosexual and heterosexual). In the past few years the number of migrant prostitutes in Barcelona has increased considerably, and some information suggests that this city has become a popular destination for men to meet and practice risky homosexual sex. We undertook this study to determine the prevalence of CT, NG, and HIV-1 in two populations at risk for STIs in Barcelona, namely female street prostitutes and male and female STI clinic attendees. Sexually transmitted C. trachomatis, N. gonorrhoeae, and HIV-1 in Barcelona HIV-1 detection in street prostitutes was performed in urine due to the difficulties in performing venous punctures in the field. The use of urine for HIV-1 diagnosis purposes is not usually seen to be convenient because antibody concentrations are lower in urine compared with those in serum11 and because of the oscillations of antibodies in urine over time.12 However, its use does appear to be appropriate for epidemiological purposes in some populations.13 In this study, IgG anti-HIV-1 antibodies were detected with the Calypte HIV-1 urine enzyme immunoassay (EIA) test (Calypte Biomedical Corp., Alameda, CA, USA) in individual samples according to manufacturer’s instructions. Samples that were initially reactive were retested in duplicate. Repeatedly positive samples were confirmed by Western blot. We could not use the Western blot initially licensed for use in urine specimens due to problems with the supplier. Hence, we used another test (Bioblot HIV-1 plus, Genelabs Diagnostic, Geneva, Switzerland) with minor variations;14 the dilutions were 3/4 for each urine (1500 mL of urine and 500 mL of blotting buffer) and the samples were incubated for 16—20 hours. Results were considered positive when reactivity to two bands including gp41, gp120, or gp160 were observed and negative when bands were not observed. Otherwise they were classified as indeterminate. Study variables and additional laboratory tests Details of sex, sexual orientation, age, origin (defined as country of birth), education, social risk factors (being or having a partner who is an intravenous drug user, being a user of other drugs, having an HIV positive partner, or being a user of prostitution), and previous history of STIs were collected from all participants. Details concerning type of partner, sexual practices, and use of condoms during the last 12 months were also collected from all participants and recorded in each site as explained before. However, information about specific sexual practices and their corresponding use of condoms by type of partner is seldom recorded in detail in the clinical histories of the STI unit at the Catalan Health Institute in Barcelona. Information on the presence of symptoms of urethritis and cervicitis was retrieved from the clinical records of subjects attending the STI clinic. Additional information related to the practice of prostitution and the reproductive health of street prostitutes was collected in the structured questionnaire and this will be presented elsewhere. Participants at the STI clinic had a serological HIV test (EIA and Western blot) and they were also offered tests for hepatitis B (antiHBc) and syphilis (rapid plasma reagin test (RPR) and Treponema pallidum hemagglutination test (TPHA)).5 The same tests were also performed for the street prostitutes who agreed to come to the STI clinic for further checkups. Data analysis Microsoft Access 97 was used for data collection and management. Results are presented separately for the two selected populations (female street prostitutes and STI clinic attendees). Statistical analyses were performed with SPSS 10.0 for 117 Windows (SPSS, Inc., Chicago, USA) and Epi Info version 6 (CDC, Atlanta, GA, USA). Prevalences of the STIs investigated (NG, CT, and HIV-1) were calculated with their corresponding 95% confidence intervals (95% CI) using the exact method. The association between categorical variables and the STI was assessed using the Chi-square test or Fisher’s exact test, as appropriate. The chosen level of significance was 5% and the p values described are two-tailed. In order to increase the numerators for the purpose of analyzing the risk of STIs in relation to condom use in different sexual practices by type of partner among female street prostitutes, a combined variable (combined test result) that included the results of the three STIs investigated was created. A positive combined test result was defined as any positive result from NG, CT, or HIV-1 testing. Results Female street prostitutes A total of 301 female street prostitutes participated in the study. Their main characteristics are shown in Table 1. With a median age of 27, around half of them were younger than 25 years old. Only 5% were autochthonous; the majority came from Latin America (31%), sub-Saharan Africa (25%), and Eastern Europe (24%) with the main countries of origin being Ecuador, Nigeria, and Romania. With regard to sexual behavior, 61% of them had a steady partner, and 28 women and 22 women, respectively, practiced anal sex with their partners and clients. Frequencies of condom use by sexual practice and type of partner are shown in Table 2; the frequency of condom use with clients was found to be high and the contrary was found with steady partners. Prevalences of NG, CT, and HIV-1 in urine samples were respectively as follows: 3.7% (95% CI: 1.8—6.4), 4.7% (95% CI: 2.6—7.7), and 1.0% (95% CI: 0.2—2.9) (Table 1). There were no statistical differences in the prevalences of the above STIs by age or origin (data not shown), with the exception of the prevalence of CT being the highest among women from Eastern Europe (12.7%) ( p = 0.01). Condom use was not a risk factor associated with having a positive combined test result, with the exception of a marginal increased risk ( p = 0.07) for prostitutes not always using condoms during vaginal sexual practices with clients (Table 2). Data from the 23 women who decided to attend the STI unit for further checkups showed prevalences of hepatitis B virus (HBV) of 34.8% and syphilis of 4.5%. Prevalences of NG, CT, and HIV-1 from 28 male street prostitutes were respectively: 0%, 0%, and 28.6%. Concerning the performance of HIV-1 testing in urine in female and male street prostitutes, overall there were 30 (9%) EIA reactive tests that required confirmation by Western blot. Following this, 11 results (three from women and eight from men) were considered positive and three (all women) indeterminate. Five of the patients with HIV-1 positive tests, three men and two women (and one with an indeterminate result too) knew they were HIV positive according to interview. None of the women who also attended the STI clinic were found to be HIV-1 positive either by urine or blood testing. 118 Table 1 M. Vall-Mayans et al. Main characteristics and STI prevalences of study participants by recruitment site Variable Female street prostitutes (n = 301) STI clinic attendeesa (n = 536) n % n % 301 — 100 — 202 334 38 62 — — — — 193 133 59 41 136 163 45 55 138 397 26 74 15 94 76 71 31 0 12 5 31 25 24 10 — 4 185 163 30 25 11 33 38 38 34 6 5 2 7 8 Education None or primary studies Secondary University 148 140 13 49 47 4 50 331 153 9 62 29 Social risk factors b Yes No 5 296 2 98 186 350 35 65 Previous STI Yes No 9 292 3 97 74 171 30 70 Type of partnerc Steady Occasional or client 184 301 61 100 227 200 42 37 Sex Female Male Sexual orientation (men) Heterosexual Homo/bisexual Age 25 >25 Origin Autochthonous Latin America Sub-Saharan Africa Eastern Europe North Africa Western Europe Other HBV (AntiHBc) Positive Negative 8 15 34.8 65.2 30 172 14.9 85.1 Syphilis (RPR and TPHA) Positive Negative 1 21 4.5 95.5 22 283 7.2 92.8 Neisseria gonorrhoeae Positive Negative 11 290 3.7 96.3 24 508 4.5 95.5 Chlamydia trachomatis Positive Negative 14 287 4.7 95.3 23 509 4.3 95.7 HIV-1 Positive Negative 3 295 1.0 99.0 13 280 4.4 95.6 Note: Totals for some categories do not add up to the number of participants as a result of missing information in some variables. a Includes 24 male and 110 female non-street prostitutes. b Social risk factors considered: being or having a partner who is an intravenous drug user, being a user of other drugs, having an HIV positive partner, or being a user of prostitution. c Non-exclusive categories. 119 Sexually transmitted C. trachomatis, N. gonorrhoeae, and HIV-1 in Barcelona Table 2 Combined STI test results by sexual practice, use of condom, and type of partner among 301 female street prostitutes Sexual practice Steady partner Vaginal Anal Oral Client Vaginal Anal Oral a b Use of condom (%) a Combined test result b Total n (%) p Value Positive n (%) Negative n (%) Yes (8) No 3 (20) 13 (8) 12 (80) 156 (92) 15 (100) 169 (100) 0.13 Yes (11) No 1 (33) 2 (8) 2 (67) 23 (92) 3 (100) 25 (100) 0.30 Yes (3) No 0 (0) 10 (9) 4 (100) 101 (91) 4 (100) 111 (100) 1 Yes (96) No 23 (8) 3 (25) 266 (92) 9 (75) 289 (100) 12 (100) 0.07 Yes (86) No 1 (5) 1 (33) 18 (95) 2 (67) 19 (100) 3 (100) 0.26 Yes (91) No 11 (6) 3 (16) 179 (94) 16 (84) 190 (100) 19 (100) 0.12 Percentage of participants that used condoms always. Combined test result from Neisseria gonorrhoeae, Chlamydia trachomatis, or HIV-1 testing. STI clinic attendees During each year of the study period, approximately 13 000 visits (60% men) took place at the STI clinic. Subjects who were invited to participate were mainly those who requested an HIV test between February and June (around four months). The response rate was 84%. Of these subjects, 536 (202 women and 334 men, 59% of them heterosexual) agreed to be screened for NG and CT by providing a urine sample in the context of this study. The main characteristics of these participants are shown in Table 1. With a median age of 32, 74% of them were over 25 years old. The majority were autochthonous (38%) and from Latin America (34%); foreigners represented 55 different countries. The prevalence of HBV was 14.9% and that of syphilis 7.2%. Concerning sexual behavior, 42% and 37% of the subjects had steady and occasional/client partners, respectively. Information available for only 96 (33%) men and women non-street prostitute heterosexuals attending the STI clinic showed that 22% of them with occasional partners never used condoms. Information on the frequency of condom use among STI clinic homo/bisexual men non-prostitutes attending the STI clinic was available for around 30 (28%) only, and depended on sexual practice; high levels of condom use in anal sex, especially with occasional partners (77%), and low levels of use in oral sex (32%) were reported. In the STI clinic setting, results for NG and CT were not available for one woman, two heterosexual men, and one homosexual man, and those for HIV were not available for 62 women, 107 heterosexual men, and 68 homo/bisexual men. Overall, prevalences of NG and CT in urine and of HIV-1 in blood samples were respectively as follows: 4.5% (95% CI: 2.9—6.6), 4.3% (95% CI: 2.8—6.4), and 4.4% (95% CI: 2.4—7.5) (Table 1). The specific rates of NG, CT, and HIV-1 by sex and sexual orientation in men that include non-street prostitutes attending the STI clinic are shown in Table 3. The prevalences of the three STIs were not statistically different after stratifying by practice of prostitution either in women ( p values for CT, NG, and HIV-1 were 1.0, 0.7, and 0.6, respectively) or in homosexual men ( p values for CT, NG, and HIV-1 were 1.0, 0.6, and 1.0, respectively). Prevalences of NG and CT were not statistically different between the three groups in Table 3 (data not shown). In addition, there were no statistical differences in those prevalences by age or origin in any of the three groups, with the exception of NG among Table 3 Prevalence of Neisseria gonorrhoeae, Chlamydia trachomatis, and HIV-1 in women and in men by sexual orientation attending the STI clinic (includes 24 male and 110 female non-street prostitutes) Women n = 201 Heterosexual men n = 191 Homosexual men n = 132 a b Neisseria gonorrhoeae Chlamydia trachomatis HIV-1 a nb % (95% CI) nb % (95% CI) n % (95% CI) 9 (1) 6 (5) 9 (8) 4.5 3.1 6.8 (2.1—8.3) (1.2—6.7) (3.2—12.5) 9 (1) 8 (2) 6 (4) 4.5 4.2 4.5 (2.1—8.3) (1.8—8.1) (1.7—9.6) 3 1 9 2.2 1.2 13.8 (0.4—6.1) (0.3—6.3) (6.5—24.7) 62 women, 107 heterosexual men, and 68 homo/bisexual men from Table 1 with missing information on HIV. Number of patients with symptoms of urethritis/cervicitis in brackets. 120 heterosexual men where men from North Africa had the highest prevalence (29%, two cases out of seven subjects) ( p < 0.001). Table 3 also shows the number of patients with symptoms of urethritis or cervicitis with positive tests. All women with a positive test for NG or CT were asymptomatic, with the exception of one. On the contrary, the majority of men with positive tests were symptomatic, with the exception of heterosexual men with a positive CT test where only two out of eight had symptoms. The prevalence of HIV-1 infection was higher among homosexual men when compared to that of heterosexual men and women ( p < 0.001) (Table 3). Discussion This study provides new information about STIs of public health importance in two different at-risk populations in Barcelona — female street prostitutes and STI clinic attendees. Prior to this study the available information on STI prevalence in these populations has been limited. It is the largest study to be carried out in Catalonia and in Spain, and the first one to use a pooling algorithm for laboratory testing, to screen at-risk populations for NG and CT using amplification-based technology in urine specimens. It is also the first one to provide HIV-1 prevalence data from street-recruited prostitutes using urine samples. Like other countries in Southern Europe,15,16 Spain is also experiencing the phenomenon of migrant prostitution. In Barcelona, a high proportion of street prostitutes are very young and with low rates of previous STIs, probably reflecting a recent commencement of prostitution. As the outreach organization provided condoms to prostitutes, it is also probable that it played a role in their high frequency of condom use with clients. Hence, it is important to recognize the pivotal role that such non-governmental organizations (NGOs) play in preventing the spread and the acquisition of STIs. In this study we document moderate prevalences of STIs among street-recruited female prostitutes, lower than those described in a similar study carried out in Italy.15 The most important finding from this part of the study is the significantly higher rate of CT infection in women from Eastern Europe, reflecting the difficulties in targeting interventions among this group.15,16 This population of female prostitutes seems to be very mobile, traveling as tourists, seldom using condoms, and the NGO Àmbit Dona reported a high frequency of voluntary abortions among them during the study period. In Europe, HIV infection rates are low in female sex workers who do not use intravenous drugs, even among foreign-born women.8,17 However, HIV rates are much higher in male prostitutes,18 as also indicated in this study, bearing in mind the limitations mentioned. Interventions facilitating the diagnosis and treatment of STIs,6 like the one provided in this study, and those to prevent the spread of STIs among street-recruited foreign prostitutes extended to men, clearly need to be implemented and maintained. Our findings regarding STI clinic users give support to the relatively low prevalence of CT in our setting. Overall, it seems that the prevalence of CT varies across Europe, generally being higher in Northern Europe compared to M. Vall-Mayans et al. Southern Europe.4 In our study, the prevalence rates of CT found in the different at-risk populations studied are in the range of those found in similar populations tested in Spain using less sensitive methods,19—21 and are much lower than those found in similar study settings from other European countries, where they are even experiencing increasing rates.22 These differences provide interesting hypotheses concerning sexual behavior, bacterial ecology, and others to be tested. For example, it has been suggested that the higher frequency of sexual activity, the higher engagement in risk-taking behavior, and the lower use of barrier contraceptives may contribute to the higher prevalence of CT infection in German compared to Spanish students.23 Nevertheless, we cannot be complacent about the moderate rates of CT among STI clinic attendees in Barcelona, as a study carried out among women attending this STI clinic 10 years earlier using nucleic acid amplification methods found a prevalence of CT of only 1.06%.24 International movement of people will probably lead to an increase in the prevalence of CT in this population and the situation needs to be monitored very carefully. This, combined with the fact that CT infection is very often asymptomatic, raises the issue of whether screening for CT should be expanded to different STI clinic attendees in our setting.25 As expected, NG rates were higher in homosexual men than in heterosexuals,5,22 and the vast majority of these infections were asymptomatic in women while the contrary happened in men, both heterosexual and homosexual. The progressive increase in NG in homosexual men in Europe has been related to a reversion to risky sexual behaviors.22 The pattern of HIV infection in men and women was similar to the one previously described,7 although in this study selection bias that overestimated the prevalence of HIV in homosexual men could not be entirely ruled out. There are some possible limitations to this study. Female migrant street prostitutes are a very mobile population who work under restrictions of legal and personal issues. Hence, prevalences found at one time may not be representative of the prevalences found subsequently. However, the results of this study still provide information on the recent burden of STIs in this specific population in Barcelona. So far, the risk factors analyzed do not allow the identification of further potential strategies to reduce the burden of these infections. In any case, given the problems surrounding commercial sex, the best affordable intervention in this study population is the continuation of the services provided by the outreach NGO. Concerning the clinical setting, the anticipated sample size was not achieved, in part because of a lack of willingness to participate in some attendees and in part because of the complexities of running a research project such as this one during busy clinics. Nevertheless, the final sample size is still satisfactory in part because the prevalences found doubled the anticipated ones. The sample size that was increased at the expense of STI attendees, who were not tested for HIV, also increased the number of subjects with missing information on this variable. However, the heterogeneity of the populations studied in the clinical setting seems not to have influenced the estimation of the STI prevalences, with the exception of an overestimate of HIV in homosexual men. Sexually transmitted C. trachomatis, N. gonorrhoeae, and HIV-1 in Barcelona The mean age of participants, especially that of STI clinic attendees, might have contributed to an underestimate of the prevalence of CTand the low level of positive cases would not allow us to find differences by age. In any case, it is still plausible that our rates of CT are lower than those found elsewhere when comparing them with those in similar populations attending STI clinics.2 Further studies among younger populations might contribute to the understanding of the epidemiology of CT in our setting. The limited information concerning sexual behavior among clinic attendees should be taken circumspectly although generally speaking it fits in with current patterns of sexual behavior.22 Yet it may be useful information since this kind of data from Catalonia and Spain are nonexistent. With consideration to the HIV-1 testing in urine, both the performance of the test and the accuracy of the pooling algorithm have been satisfactorily validated.10,13 In conclusion, this study has provided new and important information about the current epidemiological pattern and prevalence of STIs in at-risk populations in Barcelona. Among street prostitutes and STI clinic attendees, CT prevalence is currently lower than in other European countries. It is possible that the prevalence of CT could increase as a result of immigration. The prevalence of CT among young people and low-risk heterosexuals needs to be investigated. The rates of NG and HIV-1 infections are higher among homosexual than among heterosexual men. The prevalence of all three STIs in all at-risk groups needs to be monitored in a rapidly changing situation. Finally, apart from the clinical benefits of case identification, an outreach screening program such as the one directed at street prostitutes, can serve as a significant vehicle for health promotion, and, as has been the case here, the fostering of collaboration between governmental and key community nongovernmental services. Acknowledgements This work was supported by FIPSE (Foundation formed by the Spanish Ministry of Health and Consumer Affairs, Abbott Laboratories, Boehringer Ingelheim, Bristol Myers Squibb, GlaxoSmithKline, Merck Sharp and Dohme, and Roche), exp. 24238/01. We thank the staff and volunteers of Àmbit Dona who facilitated the field study. Thanks are also due to the anonymous English expert who reviewed and edited the first version of this manuscript. 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