Syphilis and HIV: The Intersection of Two Epidemics

Abstract

Syphilis has been a subject of intrigue and controversy since it was first recognized in the 15th century. Coined “the great imitator,” it can manifest in a variety of ways depending on the host and stage of infection, thus making diagnosis and management difficult. HIV infection creates an additional layer of complexity: Both pathogens are sexually transmitted, and the presence of one may facilitate infection with the other. In addition, the presentation, diagnosis, and management of syphilis differ in subtle ways between HIV-infected and HIV-uninfected patients. In this review, we summarize the epidemiology, clinical presentation, diagnosis, treatment, and monitoring of syphilis in HIV-infected patients. Syphilis is a global public health problem, resulting in an estimated 12 million new infections per year.1 In the U.S., the incidence of primary and secondary syphilis has been rising and falling in 10-year cycles since the 1940s, with the lowest recorded rates occurring in 2000, followed by a resurgence over the next 10 years. Some researchers have attributed these decade-long cycles to social and behavioral changes2 — and, indeed, several recent outbreak investigations have implicated high-risk behaviors, such as anonymous sex, sex under the influence of drugs, and unprotected sex, as the basis for the latest rise in syphilis incidence.3,4,5 However, mathematical modeling suggests that these cycles are better predicted by the natural dynamics of syphilis infection than by external, behavioral factors.6 At this point, the exact contribution of each factor remains uncertain. Similar to the HIV epidemic, the current syphilis epidemic predominantly affects three groups: men who have sex with men (MSM), injection-drug users, and individuals who engage in sex for money or drugs. The CDC estimates that, in 2008, MSM accounted for more than 60% of all new diagnoses of primary and secondary syphilis in the U.S. …