HIV and syphilis: incidence rate of coinfection and syphilis reinfection in a cohort of newly diagnosed HIV patients.

Background: Syphilis represents a major public health concern disproportionately affecting HIV positive patients and, in many cases, both infections are newly diagnosed at the same time. To date, limited studies are available on syphilis incidence in patients with a new HIV diagnosis.

Methods: Patients newly diagnosed with HIV in 2010-2018 were included in the study and screening tests for syphilis were performed at baseline and at least once a year. Primary aims were to analyze the incidence rate of HIV-syphilis coinfection and syphilis reinfection. Secondary objective was to identify characteristics independently associated with coinfection and reinfection.

Results: Of 500 newly diagnosed HIV patients, 20% presented a concomitant positive syphilis serology. Among them, 54 patients had a serology indicative for an active syphilis requiring therapy, while 46 had a history of prior treatments. The independent factors for syphilis acquisition were: MSM contact (OR=2.64; 95% CI: 1.48-4.72; P<0.001), male gender (OR=2.43; 95% CI: 1.08-5.48; P=0.032), and age (OR=1.03; 95% CI: 1.01-1.05; P=0.005 per year increasing). Presence of syphilis at the time of HIV diagnosis remained fairly stable during the study period (P for trend, P=0.689). We observed 52 syphilis reinfections related to 37 people. Patients with at least one reinfection were all males and 86.5% MSM.

Conclusions: Males and MSM with HIV presented high rates of syphilis coinfection and reinfection suggesting persistent high-risk sexual behaviors and the need for appropriate intervention strategies in order to early detect and treat syphilis avoiding life-threatening complications and the spread of the infection in the community.