Risk Factors and Incidence of Syphilis in Human Immunodeficiency Virus (HIV)-Infected Persons: The HIV Outpatient Study, 1999-2015.

Background: Since 2000, the incidence of syphilis has been increasing, especially among gay, bisexual, and other men who have sex with men (MSM) in the United States. We assessed temporal trends and associated risk factors for newly diagnosed syphilis infections among human immunodeficiency virus (HIV)-infected patients during a 16-year period.

Methods: We analyzed data from the HIV Outpatient Study (HOPS) cohort participants at 10 US HIV clinics during 1999-2015. New syphilis cases were defined based on laboratory parameters and clinical diagnoses. We performed Cox proportional hazards regression analyses of sociodemographic, clinical, and behavioral risk factors for new syphilis infections.

Results: We studied 6888 HIV-infected participants; 641 had 1 or more new syphilis diagnoses during a median follow-up of 5.2 years. Most participants were male (78%), aged 31-50 years, and 57% were MSM. The overall incidence was 1.8 (95% confidence interval [CI], 1.6-1.9) per 100 person-years (PY) and it increased from 0.4 (95% CI, .2-.8) to 2.2 (95% CI, 1.4-3.5) per 100 PY during 1999-2015. In multivariable analyses adjusting for calendar year, risk factors for syphilis included age 18-30 years (hazard ratio [HR], 1.3 [95% CI, 1.1-1.6]) vs 31-40 years, being MSM (HR, 3.1 [95% CI, 2.4-4.1]) vs heterosexual male, and being non-Hispanic black (HR, 1.6 [95% CI, 1.4-1.9]) vs non-Hispanic white.

Conclusions: The increases in the syphilis incidence rate through 2015 reflect ongoing sexual risk and highlight the need for enhanced prevention interventions among HIV-infected patients in care.