Increasing Incidence of Syphilis in People With HIV

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Among the 641 participants who were diagnosed with incident syphilis, most (85%) had CD4 cell counts at or above 200 cells/mm3 at the time of infection.
Among the 641 participants who were diagnosed with incident syphilis, most (85%) had CD4 cell counts at or above 200 cells/mm3 at the time of infection.

The incidence rate of syphilis in people with HIV increased through 2015, according to new research published in Clinical Infectious Diseases.

Since 2000, the incidence of syphilis has increased among gay, bisexual, and other men who have sex with men (MSM) in the United States. This represents an ongoing sexual risk, and temporal trends and associated risk factors for newly diagnosed syphilis infections among people with HIV were therefore investigated.

Data from HIV Outpatient Study cohort participants visiting 10 clinics in the United States from 1999 to 2015 were analyzed. A total of 6888 participants with HIV were included, and 641 had one or more new syphilis diagnoses during a median follow period of 5.2 years. Participants were mostly male, age 31 to 50 years (78%), and the majority were MSM (56%). 

The overall incidence of syphilis was 1.8 per 100 person-years (95% CI, 1.6-1.9). The incidence rate increased from 0.4 (95% CI, 0.2-0.8) to 2.2 (95% CI, 1.4-3.5) per 100 person-years during the study period.

Multivariable analyses adjusting for year found that risk factors included being age 18 to 30 years (hazard ratio [HR] 1.3; 95% CI 1.1-1.6) vs 31 to 40 years, being an MSM (HR 3.1; 95% CI, 2.4-4.1) vs a heterosexual male, and being non-Hispanic black (HR 1.6; 95% CI 1.4-1.9) vs non-Hispanic white.

This study was limited in studying the rates of treatment and cure, as most patients opted for treatment outside of a HIV Outpatient Study facility. The possibility that some diagnoses occurring at baseline visits were in fact latent and not newly acquired may lead to an overestimation of syphilis rates by no more than 10%, stated the investigators. It was also noted that trends in incidence may be in part influenced by improved screening and detection of asymptomatic infections.

The results of this study revealed a growing incidence of syphilis among younger, non-Hispanic/Latino MSM and highlight the need for ongoing testing and risk reduction interventions in this population.

Reference

Novak RM, Ghanem A, Hart R, Ward D, Armon C, Buchacz K; HIV Outpatient Study Investigators. Risk factors and incidence of syphilis in HIV-infected persons, the HIV Outpatient Study, 1999-2015 [published online April 24, 2018]. Clin Infect Dis. doi: 10.1093/cid/ciy348

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