What have been the United States syphilis incidence trends over the past 15 years, including primary and secondary (P&S) syphilis, early latent syphilis, congenital syphilis, and differences by sex and men who have sex with men (MSM)?

Syphilis Rates in the United States Over the Last 15 Years

Dramatic Reversal: From Near-Elimination to Epidemic Resurgence

Syphilis rates in the United States have undergone a complete reversal over the past 15 years, rising from historic lows around 2000 (2.1-2.2 per 100,000) to more than doubling by 2013 (5.3 per 100,000), with the epidemic now concentrated overwhelmingly among men who have sex with men while also showing concerning increases in women and congenital cases. 1, 2

Primary and Secondary (P&S) Syphilis Trends

The Historic Low Point and Subsequent Rise

• The year 2000 marked the lowest recorded rate of primary and secondary syphilis in U.S. history at 2.1 per 100,000 population, representing what appeared to be near-success of the CDC's syphilis elimination program launched in the late 1990s. 1, 2

• Between 2005 and 2013, P&S syphilis rates increased progressively among men of all ages, races, and ethnicities across all U.S. regions, with an accelerated increase in recent years showing the largest gains among MSM. 2

• By 2013, the national P&S syphilis rate had climbed to 5.3 per 100,000, representing a 152% increase from the 2000 nadir. 2

Geographic Concentration Patterns

• The initial decline through 2000 was accompanied by extreme geographic clustering, with half of all new cases concentrated in only 22 of 3,115 U.S. counties (<1%), primarily in the southern United States. 1

• This geographic concentration initially suggested elimination was achievable, but subsequent years saw geographic spread as rates increased nationally. 1

Men Who Have Sex with Men (MSM): The Driving Force

Epidemic Proportions in MSM Population

• Among MSM specifically, P&S syphilis rates reached 228.8 per 100,000 in 2013, representing rates more than 40 times higher than the general population. 3

• Projections from 2015 indicated that rates among MSM would soon approach those last seen in 1982 (estimated 340.7 per 100,000), suggesting continued acceleration of the epidemic in this population. 3

• The resurgence among MSM can be attributed to changing social and behavioral factors, particularly among young MSM, including risk compensation behaviors related to HIV prevention strategies such as pre-exposure prophylaxis (PrEP). 4

Recent Outbreaks

• Recent outbreaks have been documented among MSM in urban areas throughout the United States, reversing earlier declines seen during the 1980s-1990s. 1

Trends Among Women and Heterosexuals

Initial Increase Followed by Decline

• Among women, P&S syphilis rates increased during 2005-2008, then decreased during 2009-2013, though trends varied by race/ethnicity. 2

• By 2013, the rate among women was 0.9 per 100,000, substantially lower than among men but occurring in isolated outbreaks plus persistent low-level transmission in certain counties. 3

Geographic and Demographic Patterns

• Syphilis among women occurs primarily in isolated outbreaks among heterosexuals, which can be controlled through intensive screening, treatment, and partner notification. 3

Congenital Syphilis: A Concerning Parallel Trend

• Congenital syphilis trends closely follow P&S syphilis trends among women, making control of syphilis in women critically important for preventing infant infections. 3

• Between 1997 and 2000, congenital syphilis rates decreased by more than 50% as part of the elimination effort. 1

• However, the recent increase in syphilis among premenopausal women has coincided with a concerning rise in congenital cases, reversing earlier gains. 4

Persistent Racial and Ethnic Disparities

Dramatic Inequities

• Racial/ethnic disparities in syphilis have persisted and in some cases worsened over the 15-year period, with rates among Black persons remaining disproportionately high. 2

• In 2000, Black persons had rates approximately 23 times greater than white persons. 1

• These disparities likely reflect social determinants of health, including socioeconomic status, rather than biological factors. 2

Historical Context

• The black-to-white incidence rate ratio increased dramatically from 14.5 in 1981 to 47.8 in 1989, and these disparities have persisted into the modern era. 5

Early Latent Syphilis Patterns

• Early latent syphilis (defined as latent infection acquired within the preceding 12 months with documented seroconversion) follows similar epidemiologic patterns to P&S syphilis, concentrated among MSM. 6

• The distinction between early and late latent syphilis requires documented timing of seroconversion rather than relying on nontreponemal titers alone. 6

Critical Public Health Implications

The Failed Elimination Effort

• The CDC's national syphilis elimination program, launched around 2000 with goals to reduce P&S syphilis to no more than 1,000 cases (0.4 per 100,000) by 2005, ultimately failed as rates reversed course and began climbing. 1

• Between 1997 and 2000, adult syphilis initially decreased by 30%, but this progress was not sustained. 1

HIV Co-infection Concerns

• The biological association between syphilis and HIV transmission/acquisition creates compounded individual and healthcare burdens, making the syphilis resurgence particularly alarming. 4

• Some HIV prevention efforts may inadvertently facilitate syphilis transmission through risk compensation behaviors. 4

Current Epidemic Characteristics

• The current epidemic represents a complete reversal from the optimistic elimination goals of the early 2000s, with syphilis now firmly re-established as a major public health problem in the United States. 4, 2

• Unlike historical patterns showing cyclical epidemics every 7-10 years, the current increase appears sustained and accelerating, particularly among MSM. 7, 2