About the SHIELD Project
The Syphilis Crisis
Syphilis rates have quadrupled over the past decade, reaching their highest levels since the 1950s. One in every 1,300 US births in 2021 was complicated by congenital syphilis – a public health catastrophe. Increases in syphilis have been seen across the US: 45% of counties have seen a doubling in primary, secondary, and early latent syphilis over the past five years.
The Intersection of Syphilis and HIV
The US syphilis epidemic is closely tied to the HIV epidemic. In recent years, 25-50% of US syphilis infections occur among people with HIV (PWH). PWH have a disproportionately high risk of acquiring syphilis, with reported incidence of 2% to 6% per year (up to 13% in young adults with HIV) – rates an order of magnitude higher than for non-HIV infected peers.
Furthermore, a diagnosis of syphilis often precedes HIV infection – up to 1 in 20 men who have sex with men (MSM) were diagnosed with HIV within a year of syphilis diagnosis – and syphilis may play a causal role in HIV acquisition.
Disparities and Patterns
Syphilis and HIV both disproportionately affect racial, ethnic, and sexual minorities, and new infections are concentrated among the young. 34% of cases of primary and secondary syphilis were among men who have sex with men (MSM), and 57% were among those under 35 years old.
Syphilis case rates among Hispanics were 2.4 times those of White Americans; Black Americans had a rate five times as high. Rates of congenital syphilis in Hispanic mothers were twice that of mothers of White race, and Black mothers experienced a rate four times that of White mothers.
Research Gap
Despite extensive applications in HIV and other sexually transmitted infections, there is a marked lack of modeling studies focusing on US syphilis over the last decade. This gap hinders the effective formulation of evidence-based policy to halt the rise of the US syphilis epidemic.
Our Approach
The SHIELD model will characterize syphilis transmission, progression, HIV co-infection, and STI care engagement, while accounting for age, racial and ethnic disparities, risk profiles, and social determinants of health. We will calibrate our models to the 32 US cities which contain EHE priority jurisdictions – comprising 60% of syphilis cases as well as 60% of HIV diagnoses in 2021.
Our Vision
By developing rigorous mathematical models that integrate syphilis and HIV dynamics, we aim to provide public health officials with the evidence-based tools they need to effectively combat the syphilis epidemic and reduce health disparities.