Syphilis co-infection with HIV/AIDS : study of a local cohort in Hong Kong

Background In the recent decade resurgence of syphilis was noted in a global scale, especially in high-risk communities like men who have sex with men (MSM) and commercial sex workers (CSW). Syphilis co-infection is important in people living with human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS) because of their similar transmission routes, mutual interactions at pathophysiology level, relation to socioeconomic factors and public health implications. Methods Retrospective analysis of syphilis co-infections among the HIV/AIDS patients who have been under the care of the AIDS Clinical Service, Queen Elizabeth Hospital of Hong Kong which has served as a tertiary referral center since the beginning of the AIDS epidemic. Details of syphilis co-infection including their clinical stages on diagnosis, evidence of central nervous system (CNS) invasion and recurrence were analyzed. Results In the 1,567 subjects studied 223 (14.2%) had HIV/syphilis co-infection. There are significantly more MSM in the HIV/syphilis co-infected group (P < 0.001). Among the coinfected, 111 (49.8%) had undiagnosed and untreated syphilis at the time of HIV/AIDS diagnosis. Sixty two subjects (27.8%) acquired syphilis as totally new infections after followed up for HIV/AIDS, with a median time of 284.6 weeks (range 3.7-862.3 weeks). Twenty subjects (9.0%) showed evidence of neurosyphilis on cerebrospinal fluid study. Thirty two (14.3%) had recurrent syphilis infections and more than 80% of them occurred in MSM. The total follow up duration was 8616.58 person-years. By Poisson regression, the adjusted total syphilis incidence was 7.07 cases per 100 person-years. MSM had the highest syphilis incidence of 20.25 cases per 100 person-years. In addition syphilis incidence in MSM recruited after the year 2000 was higher than those MSM recruited before. When Comparing subjects with HIV infection diagnosed before 2000 with those having HIV infection diagnosed after 2000, latter have higher cumulative incidence of first syphilis events (P < 0.001). Using Cox regression analysis, MSM (hazard ratio 3.26, 95% CI 1.93 – 5.51, P < 0.0005), bisexual contact (hazard ratio 2.95, 95% CI 1.49 – 5.82, P < 0.005) and infection with HIV-1 subtype B (hazard ratio 1.65, 95% CI 1.08 – 2.53, P = 0.02) were associated with development of first event of syphilis infection during follow up. Conclusions The result of this study corresponded to the global trend of HIV/syphilis syndemic. New and recurrent syphilis infections continued to appear after combination antiretroviral therapy (cART) initiation. MSM, bisexual subjects and infection by HIV-1 subtype B were risk factors for syphilis events. MSM contained the highest syphilis burden. Urgent attention and measures are needed to target syphilis and HIV infection in the Hong Kong MSM population.published_or_final_versionPublic HealthMasterMaster of Public Healt