PhD candidate University of Colorado, Aurora, Colorado Denver, United States
Background: Syphilis rates have been increasing since 2016 despite decades of public health intervention. Current guidelines recommend routine testing for pregnant women, men who have sex with men, and patients with HIV. We hypothesize identifying and screening additional populations with elevated syphilis risks could help decrease syphilis rates.
Objectives: To describe changes in the prevalence of syphilis risk factors in the Colorado population from 2010-2020 and identify populations at risk of syphilis who may be missed with current testing guidelines.
Methods: This was a retrospective cohort study of syphilis cases in Colorado from 2010-2020 using Colorado Department of Public Health and Environment (CDPHE) data. Variables include patient demographics, infection characteristics, syphilis risk factors and history of other sexually transmitted infections (STIs). The overall infection rate was calculated using CDPHE population estimates. The primary outcome was the prevalence of syphilis risk factors. The prevalence of risk factors was calculated as the proportion of syphilis cases with the risk factor among all syphilis cases. Changes in the prevalence of risk factors are described for two cohorts: past (2010-2015) and present (2016-2020).
Results: There were 8,586 syphilis infections among 7,236 patients: 2,667 (31%) in the past and 5,919 (69%) in the present cohort. The infection stages were early latent (34%), late latent/unknown duration (30%), secondary (21%), and primary (15%). There were 48 ( < 1%) cases of congenital syphilis, all in the present cohort. Between the past and present cohorts, the average annual incident syphilis cases increased 166% (444 to 1,183 cases) and the average annual infection rate increased 162% (7.9 to 20.7 cases per 100,000). The proportion of cases among cis-women increased 150% (6% to 15%) from past to present while the proportion of cases among patients with HIV decreased 34% (41% to 27%). The past cohort had a higher prevalence of cases reporting multiple partners (27% vs 16%), anonymous partners (50% vs 37%), and condomless sex (16% vs 12%) compared to the present. The prevalence of injection drug use and homelessness did not change. Cases reporting an STI in the year prior to syphilis diagnosis increased from the past to present cohort: gonorrhea 144% (4% to 9%) and chlamydia 112% (4% to 9%).
Conclusions: Syphilis cases from 2010-2015 compared to 2016-2020 included more cis-women and fewer individuals reporting syphilis risk factors: HIV+, multiple/anonymous partners, condomless sex. These population changes suggest current testing guidelines may need updating. Future research should investigate the effectiveness of expanding testing among cis-women and improving syphilis testing for patients with other recent STIs.
