What underpins the decline in syphilis in Southern and Eastern Africa? An exploratory ecological analysis

• It is unclear what role AIDS mortality played in the dramatic reduction in syphilis prevalence in Southern and Eastern Africa.
• We found there was a strong positive association between peak-HIV prevalence and syphilis prevalence early in the HIV epidemic in countries in this region.
• This linear relationship between HIV prevalence and syphilis prevalence switched to a negative direction late in the HIV epidemic.
• This could be indicative of AIDS mortality having played a significant role in the decline of syphilis prevalence.
• With AIDS deaths declining in sub-Saharan Africa, vigilant surveillance of syphilis prevalence will be necessary to detect a potential re-emergence of syphilis and other STIs.

SummaryBackgroundAIDS mortality played an important role in the decline in syphilis prevalence in the USA, but its effect on the dramatic reduction in syphilis prevalence in Southern and Eastern Africa has not been explored. In this ecological study, we investigated the extent to which the relationship between syphilis and HIV prevalence at a population level varied between the early and late periods of the HIV epidemic.MethodsWe performed linear regression analysis to measure the association between the national prevalence of syphilis and the peak-HIV prevalence in the early and late phases of the HIV epidemic in 11 countries of Southern and Eastern Africa.ResultsOur analysis showed a strong positive association between peak-HIV prevalence and syphilis prevalence early in the HIV epidemic (R2 = 0.59; p = 0.006). Although only of borderline statistical significance, this linear relationship between HIV prevalence and syphilis prevalence switched to a negative direction late in the HIV epidemic (R2 = 0.32; p = 0.07).ConclusionsAIDS mortality may have played an important role in the decline in syphilis in this region. Consequently, with AIDS deaths declining in Sub-Saharan Africa, vigilant surveillance of syphilis prevalence will be necessary to detect a potential re-emergence, as has occurred in high-income countries, and to render a timely public health response.