Since the global outbreak of HIV/AIDS, HIV has been transmitted among different vulnerable populations. According to a recent review, the global trend of HIV-1 infection among men having sex with men (MSM) has continued to increase, especially in East Asia, Africa, and Russia [1]. As of September 2011, there were 22, 335 known cases of HIV infection in Taiwan, and Taiwanese nationals accounted for 96.5% of those cases. Of the Taiwanese nationals, 92.5% were male. Populations at risk for HIV infection include injection drug users (30.4%), homosexual men (38.3%), heterosexual men (21.6%), and bisexual men (8.1%). Therefore, MSM are a high risk group for HIV infection in Taiwan [2].

Since 1996~1997, the use of highly active antiretroviral therapy (HAART) has significantly decreased HIV/AIDS-related mortality [3]. It has been reported that unprotected sex has increased among MSM after the introduction of HAART, which has resulted in dramatic decreases in the morbidity and mortality from HIV-1 infection [4]. Taiwan began to provide free HAART to all HIV-1/AIDS patients in April 1997 [5, 6]. Although successful HAART can reduce the contagiousness of HIV-1, the fact that HIV-1 transmission still occurs in the ART-era indicates that transmission occurs from undiagnosed, untreated, or unsuccessfully treated patients [7].

Risks factors for HIV-1 infection in MSM include unprotected anal intercourse [8–10], multiple sexual partners [11], a history of drug use [12–14], a history of commercial sexual transactions [11, 15], and a history of other sexually transmitted diseases (STDs) [1]. In Taiwan, homosexuals usually gather in parks, gay bars, and gay saunas, and because gay saunas provide the opportunity for sexual intercourse, individuals who frequent saunas are at a high risk of contracting STDs. Therefore, gay saunas are an ideal place for voluntary counseling and testing for HIV-1 infection [16]. The aims of this study were (1) to determine the prevalence and trends of HIV-1 infection among MSM frequenting gay saunas from 2001 to 2005; (2) to identify the risk factors associated with HIV-1 infection; and (3) to determine the viral subtypes of HIV-1 strains found in MSM in Taiwan.

The mean age of participants was 32.4 (SD, 8.1) years, with a range of 17~81 years. Among participants, 54.87% had a high school degree, and 91.7% were single (Additional file 1). Significant differences were found between participants who brought their own condoms to the sauna every visit (79.5% HIV-1 positive vs. 66.9% HIV-1 negative, p < 0.05). Among those who did not bring their own condoms, more HIV-1-positive participants than their counterparts purchased condoms from the counter (53.3% vs. 39.1%, p < 0.05) (Additional file 2).

HIV-1-positive participants had sexual intercourse with more people in a 3-month period on average than their counterparts (4.8 ± 5.1 vs. 4.0 ± 6.4, p < 0.05). More HIV-1-negative than HIV-1-positive participants had insertive roles (35.9% vs. 19.5%). Overall, 27% of study participants were circumcised, including 16.5% HIV-1-positive and 26.8% HIV-1-negative participants (p = 0.045) (Additional file 3). The major reasons for testing or not were shown in Additional file 4. Nineteen percent of the study participants had an STD history (Additional file 5).

Consistent tree topologies were observed in both the NJ and ML trees. Analysis of the env subtype in 52 HIV-1-positive participants showed that all participants had subtype B (Additional file 6). Results showed that some HIV-1 strains from gay saunas and Venereal Disease Control Institute (VDCI) clustered with bootstrap values of > 85%.

According to the Centers for Disease Control, in 2009, the HIV-positive rate based on screening at major hospitals, blood centers, military bases, and prisons was 54.96/100, 000 (1651/3, 003, 735) [2]. In this study, we screened 1, 093 participants and found a syphilis-positive rate of 7.6% and a HIV-1-positive rate of 7.4%, which were significantly higher than those reported by the Centers for Disease Control.

From a physiological point of view, the strong diffusion capabilities of the rectum facilitate HIV infection [20]. Analysis by the number of sexual partners showed a direct correlation between the number of sexual partners and the probability of HIV infection [21]. In addition, condom use can significantly decrease propagation of the HIV virus. In this study, over 80% of study participants had anal intercourse, which was comparable to the 71.4% reported by Ko et al. in 1997 [21]. The percentage of participants wore a condom every time and for the entire duration of sexual intercourse (Additional file 3) was similar to that reported by Ko et al. [21], suggesting that through the years, the proportion of homosexuals performing anal intercourse has remained unchanged and the proportion of condom use has remained low.

Frequent visits to saunas increase the probability of contracting STDs [16]. Participants in our study had a higher rate of STDs, and participants with STDs are more susceptible to HIV infection (Additional file 5). The route of STD transmission is a risk factor for HIV infection and that STDs increase the HIV infection rate 2~5-fold [22]. A stepwise multiple regression analysis revealed that role played during anal intercourse, the number of sexual partners during each sauna visit, and the circumcision status were risk factors associated with HIV-1 infection in MSM frequenting gay saunas. These were also found to be risk factors in other countries [16, 22].

Male circumcision is a religious commandment in Judaism and Islam. The world prevalence of men with circumcision is 12.5%~33%, and is especially high in the USA, Canada, and Africa and among Islamic people [23]. Approximately 80% of US men are circumcised [24], in which white males had the highest prevalence (> 70%) and Hispanics had the lowest prevalence (≤ 40%) [25]. Ko et al. reported that the prevalence of circumcision in Taiwan was 7.2%~8.7% [26]. In this study, our findings indicated that circumcision of MSM provides a certain degree of protection against HIV-1 infection. Previous studies showed that male circumcision reduced the likelihood of female-to-male transmission of HIV-1 infection by 50%~60% [27–29]. Concerning the protective effect of circumcision for MSM, several studies reported that circumcision had a significant protective effect [30–33]. In contrast, other studies reported that circumcised MSM had greater chances for contracting HIV infection although they were statistically nonsignificant [34, 35]. Since Buddhism and Taoism are the two main religions in Taiwan (44.5% and 24.1%, respectively), while Christianity and Islam populations are relatively small (10% and 1%, respectively) [36], religion might not have been a confounder in this study. Recently, an emerging epidemic among Taiwanese MSM was revealed when the number of new HIV-infected homosexuals increased from 571 (17% of all new HIV-infected) in 2005 to 1, 275 (71%) in 2010 [37]. Circumcision may be one of the approaches that should be adapted to control the epidemic of HIV-1 infection among Taiwanese MSM in the future.

HIV screening among high-risk group is cost-effective. Unlinked anonymous testing can provide high-risk individuals with a secure means of testing and can prevent a selection bias [38]. In this study, we performed purposive sampling and snowballing in order to increase the sample size [39]. However, because the sampling was not random, results from this study cannot be used to represent the prevalence of HIV infection in gay sauna patrons or of the general MSM population across Taiwan. In addition, because the screening was anonymous, most participants used aliases, and only a few participants agreed to be followed-up. This hindered our follow-up efforts and impeded us from estimating the incidence in a cohort study. The seropositive rate in this study was high. We therefore suggest that future studies expand the sampling area and survey other places where MSM congregate so as to estimate the size of the MSM population and thereby fully monitor trends of the HIV virus in this high-risk population.

Of MSM participating in this study, 7.4% (81/1093) were infected with HIV-1, and all of them had subtype B. The circumcision status, the role played during anal intercourse, and the number of sexual partners during each sauna visit were the three main risk factors for HIV-1 infection.

This study accessed gay saunas to obtain a deeper understanding of the sexual behavior of MSM in Taiwan. Results from this study can serve as a reference for researchers interested in these behavioral patterns and for local authorities promoting health education among MSM.