The PICASSO Cohort: baseline characteristics of a cohort of men who have sex with men and male-to-female transgender women at high risk for syphilis infection in Lima, Peru

Despite syphilis being a curable sexually transmitted infection (STI) with proven diagnostics and known treatment and prevention strategies, it is estimated that 6 million incident syphilis cases occur worldwide annually [1]. In South America and Peru, research indicates that syphilis is hyperendemic among men who have sex with men (MSM) and male-to-female transgender women (transwomen) [2‐4]. In 2008, the prevalence of syphilis infection, verified by laboratory testing, was estimated to be 28.9% among MSM in Lima, Peru [5].

As evidenced by persistent incident syphilis infection among MSM and transwomen in Peru, current screening and management strategies are inadequate [6]. Syphilis is associated with increased risk of HIV infection, therefore quality prevention and treatment measures could have the added benefit of mitigating HIV acquisition and transmission [7]. Indeed, more research is needed to characterize determinants of syphilis among groups who are at highest risk. To better address ongoing endemic infections, these data will be presented to the Ministry of Health of Peru with recommendations to guide HIV and syphilis infection control strategies in Peru [8]. In this manuscript, we report baseline characteristics and behaviors associated with incidence of recently acquired syphilis infection using quality laboratory testing and results from socio-demographic and behavioral surveys among a clinic-based observational cohort of MSM and transwomen in Lima, Peru.

From May 2013 to May 2014, 401 participants, 312 MSM and 89 transwomen, were recruited into the PICASSO cohort in Lima, Peru. The median ages of MSM and transwomen were 29.0 and 32.5 years (interquartile ranges [IQR]: 23.3, 37.4 and 27.2, 39.5, respectively). Among participants, 27.9% of MSM and 76.5% of transwomen earned less than minimum wage (approximately $250 USD per month; Table 1). In survey results collected from participants prior to laboratory testing, 35.6% of MSM and 39.3% of transwomen reported a prior diagnosis of syphilis and 24.1% of MSM and 27.6% of transwomen reported a prior diagnosis of HIV infection. Among participants with a self-reported prior diagnosis of HIV infection, 54.8% of MSM and 52.4% of transwomen reported that they were not using ART (Table 1). MSM reported that during anal sex, 50.3% were a versatile partner (i.e. having receptive and insertive anal sex), 21.8% were a receptive partner, and 27.9% were an insertive partner. Transwomen reported that during anal sex, 30.3% were a versatile partner, 67.4% were a receptive partner, and 2.3% were an insertive partner. The median number of recent male or transwomen sex partners reported by MSM and transwomen was 4 (IQR: 2, 7) and 15 (IQR: 5, 40), respectively.

Among our participants with a prior diagnosis of HIV, 54.8% of MSM and 52.4% of transwomen reported that they were not on ART (Table 1). Among HIV infected MSM not taking ART, 23.5% had recently acquired syphilis infection detected by laboratory testing and 64.7% had a diagnosis of a STI in the last 6 months. Among HIV infected transwomen participants not taking ART, 9.1% had recently acquired syphilis infection detected by laboratory testing and 45.5% had a diagnosis of a STI in the last 6 months.

Of the inclusion criteria needed for inclusion, the majority of the cohort reported over 5 years of sexual activity, more than five events of condomless anal sex in the past 6 months, and more than five sex partners in the past 3 months (Table 2).

The PICASSO cohort study successfully recruited 401 at risk participants, 312 MSM and 89 transwomen, with a high baseline prevalence of recently acquired syphilis infection in Lima, Peru. Among participants, the prevalence of recently acquired syphilis infection was 16.8% among MSM and 6.7% among tranwomen and HIV infection was 30.1% among MSM and 33.7% among transwomen participants. Among participants with recently acquired syphilis infection, STI and HIV co-infection were high. We found that recently acquired syphilis infection was independently associated with younger age, receptive anal sex, rectal bacterial STIs, self-reported prior HIV diagnosis, and prior syphilis diagnosis.

A limited number of studies report syphilis data in Peru. A study conducted prior to the introduction of ART showed a decrease in recently acquired syphilis infection (defined as a VDRL or RPR titer ≥1:16) from 8.6 in 1996 to 3.4% in 2002 [15]. Among MSM, two studies conducted after introduction of ART estimated the prevalence of recently acquired syphilis infection was 5.4 and 10.5% [16, 17]. Another study from 2012 reported that among HIV uninfected MSM and transwomen, 18% had positive serology for syphilis [18]. Prior studies differ from our cohort because we sampled at-risk MSM and transwomen recruited from HIV/STI clinics in the post-ART era. Our cohort was thoroughly surveyed and tested and was found to have a high incidence of recently acquired syphilis infection.

Prior reports described independent associations between recently acquired syphilis infection and HIV infection, increased number of years of sexual activity, and condomless anal intercourse among MSM and transwomen [16, 19]. We found that recently acquired syphilis infection was independently associated with rectal bacterial STIs and self-reported HIV diagnosis.

We found that among participants with a prior diagnosis of HIV, the majority of MSM and transwomen were not on ART. Among HIV-infected MSM and transwomen participants not taking ART, many participants had a recently acquired syphilis infection detected by laboratory testing and about half of all participants had a diagnosis of any STI in the last 6 months. Those data imply that HIV-infected MSM and transwomen not on ART had recent sex with increased risk of HIV infection transmission [20]. Improved management of HIV infection among MSM and transwomen is needed in Peru to prevent further spread of infection.

Our study has the following limitations. The clinic-based cohort was neither population-based nor randomly selected. We had limited statistical power to compare MSM versus transwomen in our study. Comparison analyses were conduced between MSM and transwomen in our cohort and showed no significant differences in identified risk factors. Additionally, latent class analysis was performed to ensure there were no identifiable subgroups in our cohort with regard to our primary outcome variable (i.e., recently acquired syphilis infection) [14]. The study’s inclusion criteria make it unlikely that participants were representative of MSM and transwomen in Lima, Peru.

We successfully recruited a cohort of MSM and transwomen with a high prevalence of recently acquired syphilis infection in Lima, Peru. Recently acquired syphilis infection was associated with socio-demographic characteristics, sexual risk behavior, and sexually transmitted co-infections. Because HIV transmission and acquisition is associated with recently acquired syphilis infection, public health strategies need to be updated in Peru to recommend routine syphilis screening in HIV care for MSM and transwomen.