The Impact of Syphilis on HIV Acquisition and Progression in Sub-Saharan Africa

Most people living with HIV (PLWH) are co-infected with syphilis or other sexually transmitted infections (STIs) and experience frequent reactivations of syphilis. Thus, syphilis or other STIs are highly prevalent in most regions experiencing severe HIV epidemics. In sub-Saharan Africa, the region most heavily affected by HIV, the prevalence of syphilis among PLWH is approximately 7.3%. This region accounts for 40% of global STIs and 70% of HIV cases, highlighting the need for targeted research. Despite the high prevalence of syphilis among PLWH in the region, the impact of syphilis on HIV transmission and HIV disease progression has not been well-studied. In this manuscript, we evaluated if syphilis facilitates HIV acquisition and HIV disease progression in the region. We used retrospective data from 53,915 adult participants enrolled through Population-based HIV Impact Assessment (PHIA) surveys conducted in Zambia and Tanzania. Logistic regression models were used to assess the impact of syphilis on HIV acquisition and disease progression. Our findings indicated that syphilis infection was associated with higher odds of HIV acquisition. Moreover, co-infection with syphilis was associated with higher odds of HIV disease progression among PLWH treated with antiretroviral therapy (ART). Our findings suggested that the recognition, treatment, and prevention of syphilis to reduce the risk of HIV transmission and HIV disease progression should be a public health priority in sub-Saharan Africa, where ART may not be readily available.