Syphilis

Background

Syphilis, a genital ulcerative disease caused by the bacterium Treponema pallidum, is associated with significant complications if left untreated and can facilitate the transmission and acquisition of HIV infection.^1–3 Additionally, historical data demonstrate that untreated early syphilis in pregnant women, if acquired during the 4 years before delivery, can lead to infection of the fetus in up to 80% of cases and may result in stillbirth or death of the infant in up to 40% of cases.⁴

In 2000 and 2001, the national rate of reported primary and secondary (P&S) syphilis cases was 2.1 cases per 100,000 population, the lowest rate since reporting began in 1941 (Figure 30, Table 1). However, the P&S syphilis rate has increased almost every year since 2000–2001. In 2015, a total of 23,872 P&S syphilis cases were reported. During 2014–2015, the national P&S syphilis rate increased 19.0% to 7.5 cases per 100,000 population, the highest rate reported since 1994.

During 2000–2015, the rise in the rate of reported P&S syphilis was primarily attributable to increased cases among men and, specifically, among gay, bisexual, and other men who have sex with men (collectively referred to as MSM) (Figures 31 and 32). However, during 2013–2015, the rate increased both among men and women (Tables 28 and 29). During 2014–2015, the rate increased 18.1% among men and 27.3% among women. These increases among women are of particular concern because congenital syphilis cases tend to increase as the rate of P&S syphilis among women increases (Figure 44). During 2014–2015, the national, male, and female P&S syphilis rates increased in every region of the country (Figure 33, Tables 27, 28, and 29). Nationally, P&S syphilis rates increased in every age group among those aged 15–64 years and in every race/ethnicity group except for American Indians/Alaska Natives during 2014–2015 (Figures 38 and 39, Table 34).

As in recent years, MSM accounted for the majority of reported P&S syphilis cases in 2015 (Figures 31 and 40). Nationally, the highest rates of P&S syphilis in 2015 were observed among men aged 25–29 years and 20–24 years, among men in the West and in the South, and among Black men (Figure 36, Tables 29, 34 and 35B).

Interpreting Rates of Reported Cases of Syphilis

Left untreated, infection with syphilis can span decades. Primary and secondary syphilis are the earliest stages of infection, reflect symptomatic disease, and are indicators of incident infection.⁵ For these reasons, trend analyses of syphilis focus on reported cases and rates of reported cases of P&S syphilis. When referring to “P&S syphilis”, case counts are the sum of both primary and secondary cases, and “rate of P&S syphilis” refers to this sum per unit population.

Changes in reporting and screening practices can complicate interpretation of trends over time. To minimize the effect of changes in reporting over time, trend data in this report are restricted to jurisdictions that consistently report data of interest (e.g., sex of sex partner) for each year of a given time period. Details of these restrictions are provided in the text and footnotes of the pertinent text and figures.

P&S Syphilis — United States

In 2015, a total of 23,872 cases of P&S syphilis were reported in the United States, yielding a rate of 7.5 cases per 100,000 population (Table 1). This rate represents a 19.0% increase compared with 2014 (6.3 cases per 100,000 population), and a 66.7% increase compared with 2011 (4.5 cases per 100,000 population).

P&S Syphilis by Region

In 2015, the West had the highest rate of reported P&S syphilis cases (9.6 cases per 100,000 population), followed by the South (8.1 cases per 100,000 population), the Northeast (6.6 cases per 100,000 population), and the Midwest (4.8 cases per 100,000 population) (Table 27). During 2014–2015, the P&S syphilis rate increased in every region: 23.1% in the West, 20.0% in the Northeast, 19.1% in the South, and 9.1% in the Midwest (Figure 33, Table 27).

P&S Syphilis by State

In 2015, rates of reported P&S syphilis cases per 100,000 population ranged by state from 0.9 in Wyoming to 15.0 in Louisiana (Figure 34, Table 26). During 2014–2015, P&S syphilis rates increased in 74.0% (37/50) of states, and decreased in 26.0% (13/50) of states and in the District of Columbia (Table 27).

P&S Syphilis by Metropolitan Statistical Area

The overall rate of reported P&S syphilis cases in the 50 most populous metropolitan statistical areas (MSAs) was 9.9 cases per 100,000 population in 2015, which represents a 15.1% increase since 2014 (8.6 cases per 100,000 population) (Table 30). In 2015, 72.3% of reported P&S syphilis cases (74.0% of male cases and 55.7% of female cases) were reported by these 50 MSAs. In 2015, the rate among women in these MSAs was 1.4 cases per 100,000 females, while the rate among men was 18.6 cases per 100,000 males (Tables 31 and 32).

P&S Syphilis by County

In 2015, 65.3% of reported P&S syphilis cases occurred in 70 counties or independent cities (Table 33). Of 3,141 counties in the United States, 445 (14.2%) had a rate greater than 6.4 cases per 100,000 population, 451 (14.4%) reported a rate from 2.9 to 6.4 cases per 100,000 population, 434 (13.8%) reported a rate from 0.3 to 2.8 cases per 100,000 population, and 1,811 (57.7%) counties reported no cases of P&S syphilis in 2015 (Figure 35).

P&S Syphilis by Sex and Sexual Behavior

As has been observed in previous years, in 2015 the rate of reported P&S syphilis cases among men (13.7 cases per 100,000 males) was much higher than the rate among women (1.4 cases per 100,000 females), and men account for a large majority (90.3%) of P&S syphilis cases (Figure 40, Tables 28 and 29). Among men, the rate of P&S syphilis has increased every year since 2000, and during 2014–2015, the rate among men increased 18.1% (Figure 32, Table 29). In contrast, the P&S syphilis rate among women has fluctuated between 0.8 and 1.7 cases per 100,000 females since 2000 (Figure 32, Table 28). During 2014–2015, the P&S syphilis rate among women increased 27.3%.

These increases in male and female P&S syphilis rates were observed in every region of the country during 2014–2015. Among men, the rate increased 22.2% in the West, 19.6% in the Northeast, 18.6% in the South, and 8.9% in the Midwest (Table 29). Among women, the largest increases were observed in the West (41.7%) and Northeast (40.0%), followed by the South (20.0%) and the Midwest (11.1%) (Table 28).

MSM continued to account for the majority of P&S syphilis cases in 2015 (Figures 31 and 40). Of 23,872 reported P&S syphilis cases in 2015, 14,229 (59.6%) were among MSM, including 12,891 (54.0%) cases among men who had sex with men only and 1,338 (5.6%) cases among men who had sex with both men and women (Figure 40). Overall, 3,178 (13.3%) cases were among men who had sex with women only (MSW), 2,298 (9.6%) were among women, 4,140 (17.3%) were among men without information about sex of sex partner, and 27 (0.1%) were cases reported with unknown sex (Figure 40). Among the 17,407 male cases with information on sex of sex partner, 81.7% occurred among MSM.

A total of 37 states were able to classify at least 70.0% of reported P&S syphilis cases as MSM, MSW, or women each year during 2011–2015 (Figure 31). In these states during 2014–2015, the number of cases increased 12.8% among MSM, 22.5% among MSW, and 27.1% among women.

P&S Syphilis by Age

As in previous years, in 2015, rates of reported P&S syphilis cases were highest among persons aged 24–29 years and 20–24 years (Figure 36, Table 34). In 2015, the highest rates were observed among men aged 25–29 years (41.8 cases per 100,000 males) and 20–24 years (35.7 cases per 100,000 males). Similarly, the highest rates among women were among those aged 20–24 years (5.1 cases per 100,000 females) and those aged 25–29 years (4.5 cases per 100,000 females).

During 2014–2015, the P&S syphilis rate increased in all age groups among those aged 15–64 years (Table 34). Rates increased 10.2% among those aged 15–19 years, 14.9% among those aged 20–24 years, 26.3% among those aged 25–29 years, 23.1% among those aged 30–34 years, 21.4% among those aged 35–39 years, 8.2% among those aged 40–44 years, 17.6% among those aged 45–54 years, and 31.8% among those aged 55–64 years (Table 34).

In 2015, persons aged 15–44 years accounted for 79.6% of reported P&S syphilis cases with known age. Among both men and women, the P&S syphilis rate increased during 2014–2015 in all age groups among those aged 15–44 years (Figures 37 and 38).

P&S Syphilis by Race/Ethnicity

In 2015, among the 49 states that submitted data in the race and ethnicity categories according to Office of Management and Budget (OMB) standards (see Section A1.5 in Appendix A), the rate of reported P&S syphilis cases remained highest among Blacks (21.4 cases per 100,000 population) (Table 35B). The rate among Blacks was 5.2 times the rate among Whites (4.1 cases per 100,000 population). The P&S syphilis rates among Native Hawaiians/Other Pacific Islanders (10.4 cases per 100,000 population) was 2.5 times the rate among Whites, the rate among Hispanics (9.1 cases per 100,000 population) was 2.2 times the rate among Whites, the rate among American Indians/Alaska Natives (5.6 cases per 100,000 population) was 1.4 times the rate among Whites, and the rate among Asians (3.0 cases per 100,000 population) was 0.7 times the rate among Whites (Table 35B).

During 2011–2015, among the 45 states that submitted race and ethnicity data according to OMB standards (see Section A1.5 in Appendix A) for all five years during that period, the P&S syphilis rate increased among all race/ethnicity groups (Figure 39). During 2014–2015, rates increased in every race/ethnicity group except for American Indians/Alaska Natives. The greatest increases during 2014–2015 were observed among Native Hawaiians/Other Pacific Islanders (63.1%) and those who identified as Multiracial (45.5%), followed by Hispanics (25.4%), Whites (17.6%), Asians (15.4%), and Blacks (13.1%).

More information on P&S syphilis rates among racial/ ethnic groups can be found in the Special Focus Profiles.

P&S Syphilis and HIV Co-infection

Reported cases of P&S syphilis continue to be characterized by a high rate of HIV co-infection, particularly among MSM. In 2015, 31 states were able to classify at least 70.0% of reported P&S syphilis cases as MSM, MSW, or women and at least 70.0% of reported cases as HIV-positive or HIV-negative (Figure 41). Among 49.8% of cases among MSM were HIV-positive, compared with 10.0% of cases among MSW, and 3.9% of cases among women.

P&S Syphilis by Reporting Source

In 2015, 20.1% of cases were reported from STD clinics, 72.5% were reported from venues outside of STD clinics, and 7.4% of cases had an unknown source of report (Table A2). During 2014–2015, the number of P&S syphilis cases reported by STD clinics and by non-STD clinic settings increased (Figure 42). However, the proportion of P&S syphilis cases that were reported by STD clinics has declined over the last decade from 34.2% of cases in 2006 to 20.1% of cases in 2015. In 2015, private physicians/health maintenance organizations (HMOs) and STD clinics were the most common reporting sources among MSM (27.7% and 25.4%, respectively), MSW (21.8% and 23.9%, respectively), and women (25.4% and 16.7%, respectively) (Figure 43).

Congenital Syphilis

After decreasing from 10.5 to 8.4 reported congenital syphilis cases per 100,000 live births during 2008–2012, the rate of reported congenital syphilis has subsequently increased each year during 2012–2015 (Table 1). In 2015, there were a total of 487 reported cases of congenital syphilis, for a national rate of 12.4 cases per 100,000 live births. This rate represents a 6.0% increase relative to 2014 (11.7 cases per 100,000 live births) and a 36.3% increase relative to 2011 (9.1 cases per 100,000 live births). As has been observed historically, these increases paralleled increases in P&S syphilis among women during 2014–2015 (27.3%) and during 2011–2015 (55.6%) (Figure 44, Table 28 ).

During 2014–2015, the increase in reported congenital syphilis cases was primarily attributable to an increase in the West. During this time period, the congenital syphilis rate increased 42.3% in the West, but decreased 3.5% in the Midwest, 7.7% in the South, and 17.4% in the Northeast (Table 41). In 2015, the highest congenital syphilis rates were reported from the West (18.5 cases per 100,000 live births), followed by the South (14.4 cases per 100,000 live births), Midwest (8.2 cases per 100,000 live births), and the Northeast (3.8 cases per 100,000 live births). In addition, rates were highest among Blacks (35.2 cases per 100,000 live births), followed by Hispanics (15.5 cases per 100,000 live births), American Indians/Alaska Natives (10.3 cases per 100,000 live births), Asians/Pacific Islanders (5.9 cases per 100,000 live births), and Whites (4.4 cases per 100,000 live births) (Table 42).

Syphilis — All Stages (P&S, Early Latent, Late, Late Latent, and Congenital)

In 2015, total case counts and rates for reported syphilis were the highest recorded since 1994. The total number of cases of syphilis (P&S, early latent, late, late latent, and congenital) reported to CDC increased 17.7% during 2014–2015 (from 63,453 cases to 74,702 cases) (Table 1). The number of cases of early latent syphilis reported to CDC increased 24.3% (from 19,452 cases to 24,173 cases), and the number of cases of late and late latent syphilis increased 11.2% (from 23,541 cases to 26,170 cases) (Tables 1, 36, and 38).

Syphilis among Special Populations

More information about syphilis and congenital syphilis in racial/ethnic groups, women of reproductive age, adolescents, and MSM can be found in the Special Focus Profiles.

Syphilis Summary

The national rate of reported P&S syphilis cases reached an historic low in 2000 and 2001, but has increased almost every year since then. This increase was largely attributable to an increase among men, and in particular among MSM. However, during 2014–2015, rates increased among both men and women in every region of the country. Rates of reported congenital syphilis cases also increased during 2014–2015, although this increase was primarily attributable to an increase in the West.

MSM continued to account for the majority of reported P&S syphilis cases in 2015. Nationally, the highest rates of P&S syphilis in 2015 were observed among men aged 25–29 years and 20–24 years, among men in the West and in the South, and among Black men.

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1 Jarzebowski W, Caumes E, Dupin N, et al. Effect of early syphilis infection on plasma viral load and CD4 cell count in human immunodeficiency virus infected men: results from the FHDH- ANRS CO4 cohort. Arch Intern Med 2012; 172: 1237–1243.

2 Buchacz K, Patel P, Taylor M, et al. Syphilis increases HIV viral load and decreases CD4 cell counts in HIV-infected patients with new syphilis infections. AIDS 2004; 18:2075–2079.

3 Fleming DT, Wasserheit JN. From epidemiological synergy to public health policy and practice: the contribution of other sexually transmitted diseases to sexual transmission of HIV infection. Sex Trans Infect 1999; 75: 3–17.

4 Ingraham NR. The value of penicillin alone in the prevention and treatment of congenital syphilis. Acta Derm Venereol 1951; 31(Suppl 24): 60–88.

5 Peterman TA, Kahn RH, Ciesielski CA, et al. Misclassification of the stages of syphilis: implications for surveillance. Sex Transm Dis. 2005;32(3):144-9.

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