Prevalence of chlamydial, gonococcal and syphilis positivity by anatomical site and sex via self-collected biospecimens using at-home testing kits among a large and diverse cohort of men and women enrolled in the MACS/WIHS Combined Cohort Study (MWCCS) in the USA

INTRODUCTION: (GC), the two most commonly reported bacterial sexually transmitted infections (STIs) in the USA. Similarly, MSM and transgender women have a higher number of syphilis infections in the USA than other groups. The presence of any of these three STIs is a significant risk factor for HIV acquisition and transmission, unless taking antiretroviral medication for HIV prevention (pre-exposure prophylaxis) or treatment (antiretroviral therapy). We sought to understand the prevalence rates of STIs in various vulnerable populations by anatomical site, sex and gender, which will inform the development of targeted prevention interventions and guide future updates to national testing guidelines. METHODS: Participants are enrolled in the MACS (Multicenter AIDS Cohort Study)/WIHS (Women's Interagency HIV Study) Combined Cohort Study (MWCCS)-the longest-running observational study of both people living with HIV (PLWH) and sociodemographically similar people living without HIV (PLWOH) in the world-with a total of 13 clinical research sites across the USA; participants (N=5700) complete quantitative assessments related to a variety of behavioural and health-related factors every 6 months. Regardless of whether or not they were sexually active or symptomatic/asymptomatic, all enrolled participants (ie, cisgender MSM, transgender women, cisgender women and cisgender MSW) were asked to complete surveillance testing for bacterial STIs (ie, syphilis, CT and GC). In addition to urethral samples, cisgender MSM, transgender women and cisgender MSW collected samples to test for extragenital pharyngeal and rectal CT and GC. Using at-home testing kits, participants self-collected biospecimens (ie, dried blood spots (DBS)/ microtainer of blood, urine and rectal and pharyngeal swabs) which were mailed to a central laboratory for nucleic acid amplification testing (for CT/GC) and syphilis testing using the reverse algorithm. STI results were linked to participants' HIV testing data and self-administered surveys on sociodemographics, sexual behaviours and psychosocial factors. RESULTS: Among those tested, 24.6% of cisgender MSM, 25.8% of transgender women, 7.4% of cisgender women and 14.6% cisgender MSW tested positive for at least one STI. Multiple STIs/anatomical sites were detected in 3.9% of participants, with the highest prevalence among transgender women (9.7%). Current/past syphilis prevalence was 11.2% across all participants, with cisgender MSM (19.7%) and transgender women (19.4%) having a higher prevalence than cisgender women (6.4%) and cisgender MSW (12.6%). Regarding CT, 2.1% of the participants tested were positive at one anatomical site. Among those who had extragenital testing, rectal CT was the most prevalent (3.2%), including 3.4% among cisgender MSM, 8.9% among transgender women and 0.9% among cisgender MSW. For GC, 1.4% of participants tested positive at one site. Among those who tested for extragenital STIs, rectal GC was the most common site, with a prevalence of 2.2%, including 2.3% for cisgender MSM, 4.3% for transgender women and 1.4% among MSW. Overall, 7.1% of participants tested positive for CT or GC at one or more anatomical sites. Finally, PLWH had a significantly higher prevalence of syphilis (13.74%) compared with PLWOH (6.11%) (p<0.001). CONCLUSION: There is a high prevalence of bacterial STIs among participants in the MWCCS. Self-collection of DBS/microtainer of blood, urine and rectal and pharyngeal swabs provided a useful, cost-effective option for screening participants outside of the traditional clinical setting. Given the possible asymptomatic nature of all three STIs, regular testing and education can be key to detection and treatment. Culturally appropriate and locally derived community outreach and engagement can be highly effective in reducing stigma around HIV and STIs and help reduce barriers to testing and treatment.