Syphilis in MSM 15 Times Higher Than General Population

Lucy Hicks

July 16, 2021

Worldwide, nearly 8% of men who have sex with men (MSM) may have syphilis, a new systematic review and meta-analysis suggests. This estimate, generated from 275 studies across 77 countries, is 15 times greater than the most recent estimates of syphilis prevalence in men in a general population.

"That disparity is absolutely unacceptable," said Matthew Chico, PhD, associate professor at the London School of Hygiene and Tropical Medicine, London, United Kingdom, and senior author of the review in an interview with Medscape Medical News.

Although the World Health Organization (WHO) aims to reduce the global prevalence of syphilis by 90% by 2030, an ambitious goal set in 2016, recent research suggests syphilis numbers are moving in the opposite direction. Cases in the United States rose 74% between 2015 and 2019, and other nations, such as Australia, South Korea, and the United Kingdom, are seeing similar trends.

Syphilis prevalence is generally higher in MSM, largely in subpopulations who have multiple sexual partners, said Kenneth Mayer, MD, in an interview with Medscape. Mayer is medical research director at the Fenway Institute, Boston, Massachusetts, and was not involved with the study.

Health literacy, lack of access to care, and medical mistrust can all be challenges to screening, identifying, and treating the infection in this population.

Reducing syphilis cases will require focusing interventions on higher-risk groups such as MSM, said Chico; however, there was "a real dearth in knowledge about the most likely prevalence of syphilis among MSM on a global level," he said.

To help fill in the gaps, Chico and his research team collected studies that included syphilis prevalence data for MSM published between January 1, 2000, and February 1, 2020. Researchers excluded studies that included only MSM living with HIV, injection drug users, patients who routinely visit sexually transmitted infection (STI) clinics, and people only seeking care for STIs or other genital symptoms, because these studies would have skewed global syphilis prevalence estimates higher.

Their review, published July 8 in The Lancet Global Health, found that the pooled global prevalence of syphilis from 2000–2020 in MSM was 7.5%. It ranged from 1.9% in Australia and New Zealand to 10.6% in Latin America and the Caribbean. In comparison, the WHO estimates that globally, 0.5% of men in a general population have syphilis, a 15-fold difference.

This elevated estimate is not surprising, and the review provides a more international view of syphilis. Earlier attempts to estimate the prevalence of syphilis among MSM were generally conducted in higher-income countries such as the United States, Mayer says. "It's important that clinicians recognize that this is a global health issue, so they can do the appropriate screening."

The review found that regions in which the prevalence of HIV was above 5% had higher rates of syphilis (8.7%) compared to regions in which the prevalence of HIV was below 5% (6.6%). Pooled syphilis prevalence estimates were also higher for lower-middle and upper-middle income countries (8.7% and 8.6%, respectively).

Global syphilis prevalence dipped from 8.9% in studies from 2000–2009 to 6.6% in studies from 2010–2020. In Europe, Northern America, Latin America, the Caribbean, and Oceania (excluding Australia and New Zealand), syphilis prevalence estimates for 2015–2020 were higher compared to 2010–2014.

The authors acknowledged that there were some limitations to the study, particularly that regions of Eastern and Southeastern Asia contributed more than half (54.5%) of the global data points used in the study and accounted for more than 82% of the study's participants. This highlights the lack of data from other regions around the world, Chico said.

Chico hopes these findings "serve as a clarion call to action" to focus interventions on groups at higher risk for syphilis, such as MSM, in the effort to drastically reduce syphilis cases around the world. Mayer agrees. "[Syphilis] is a readily diagnosable and treatable infection," he says. "It definitely is something that we should be able to get a handle on, but that requires paying attention to the different subgroups who have particularly high rates of the infection."

Lancet Glob Health. Published online July 8, 2021. Full text

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