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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 syphilis in pregnant women, if acquired during the four 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 35, Table 1). However, the P&S syphilis rate has increased almost every year since 2000–2001. Since 2000, the rise in the rate of reported P&S syphilis has been 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). MSM account for the majority of P&S syphilis cases, and estimated rates are substantially higher among MSM compared with men who have sex with women only (MSW) or women.5 The number of cases among MSM has continued to increase, but within the last five years, cases among MSW and women have increased substantially as well. The increase in syphilis among women is of particular concern because it has been associated with a striking increase in congenital syphilis. These recent trends highlight the importance of national syphilis surveillance to better understand the current epidemiology of syphilis in the United States and to focus prevention efforts.

Interpreting Rates of Reported Cases of Syphilis

Left untreated, infection with syphilis can span decades. P&S syphilis are the earliest stages of infection, reflect symptomatic disease, and are indicators of incident infection.6 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 partners) 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 2017, a total of 30,644 cases of P&S syphilis were reported in the United States, yielding a rate of 9.5 cases per 100,000 population (Figure 35, Table 1). This rate represents a 10.5% increase compared with 2016 (8.6 cases per 100,000 population), and a 72.7% increase compared with 2013 (5.5 cases per 100,000 population).

P&S Syphilis by Region

In 2017, the West had the highest rate of reported P&S syphilis cases (13.2 cases per 100,000 population), followed by the South (9.7 cases per 100,000 population), the Northeast (8.0 cases per 100,000 population), and the Midwest (6.2 cases per 100,000 population) (Table 27). During 2016–2017, the P&S syphilis rate increased 16.8% in the West, 10.2% in the South, and 8.8% in the Midwest; the rate did not change in the Northeast (Figure 36, Table 27).

Figure 35. Line graph showing rates of reported cases of syphilis in the United States from 1941 to 2017 by stage of infection. Data provided in table 1.

Figure 35. Syphilis — Rates of Reported Cases by Stage of Infection, United States, 1941–2017

Figure 36. Line graph showing rates of reported cases of primary and secondary syphilis in the United States from 2008 to 2017 by region (West, Midwest, South, and East). Data for 2013 to 2017 provided in table 27.

Figure 36. Primary and Secondary Syphilis — Rates of Reported Cases by Region, United States, 2008–2017

P&S Syphilis by State

In 2017, rates of reported P&S syphilis cases per 100,000 population ranged by state from 0.7 in Wyoming to 20.0 in Nevada (Figure 37, Table 26). The rate of reported P&S syphilis cases in the District of Columbia was 40.2 cases per 100,000 population. During 2016–2017, P&S syphilis rates increased in 72% (36/50) of states and the District of Columbia, and remained stable or decreased in 28% (14/50) of states (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 12.1 cases per 100,000 population in 2017, which represents a 9.0% increase since 2016 (11.1 cases per 100,000 population) (Table 30). Overall, in 2017, 70.4% of reported P&S syphilis cases (72.9% of male cases and 52.0% of female cases) were reported by these 50 MSAs. In 2017, the rate among women in these MSAs was 2.1 cases per 100,000 females, while the rate among men was 22.5 cases per 100,000 males (Tables 31 and 32).

P&S Syphilis by County

In 2017, 63% of reported P&S syphilis cases occurred in 70 counties or independent cities (Table 33). Of 3,140 counties in the United States, 531 (16.9%) had a P&S syphilis rate greater than 7.5 cases per 100,000 population, 522 (16.6%) reported a rate from 3.9 to 7.5 cases per 100,000 population, 525 (16.7%) reported a rate from >0 to 3.8 cases per 100,000 population, and 1,562 (49.7%) counties reported no cases of P&S syphilis in 2017 (Figure 38).

Figure 37. United States map showing rates of reported cases of primary and secondary syphilis in 2017 by state and outlying Areas (Guam, Puerto Rico, and Virgin Islands). Data provided in table 27.

Figure 37. Primary and Secondary Syphilis — Rates of Reported Cases by State, United States and Outlying Areas, 2017

Figure 38. United States map showing rates of reported cases of primary and secondary syphilis in 2017 by county. Data for top 70 counties and independent cities ranked by number of reported cases and then by rate provided in table 33.

Figure 38. Primary and Secondary Syphilis — Rates of Reported Cases by County, United States, 2017

P&S Syphilis by Sex and Sexual Behavior

As has been observed in previous years, in 2017 the rate of reported P&S syphilis cases among men (16.9 cases per 100,000 males) was much higher than the rate among women (2.3 cases per 100,000 females), and men accounted for a large majority (87.7%) of P&S syphilis cases (Figure 39, Tables 28 and 29). Among men, the rate of P&S syphilis has increased every year since 2000, and during 2016–2017, the rate among men increased 9.0% (Figure 40, Table 29). In contrast, the P&S syphilis rate among women fluctuated between 0.8 and 1.7 cases per 100,000 females during 2000–2013, but has increased substantially since 2013 (Figure 40, Table 28). During 2013–2017, the P&S syphilis rate among women more than doubled (increased 155.6%). During 2016–2017, the P&S syphilis rate among women increased 21.1%.

These increases in male and female P&S syphilis rates were observed in almost every region of the country during 2016–2017. Among men, the rate increased 14.5% in the West, 8.3% in the South, and 7.8% in the Midwest; the rate decreased 0.7% in the Northeast (Table 29). Among women, the largest increases were observed in the West (29.6%), followed by the South (22.7%), the Northeast (11.1%) and the Midwest (8.3%) (Table 28).

MSM continued to account for the majority of P&S syphilis cases in 2017 (Figures 39 and 41). Of 30,644 reported P&S syphilis cases in 2017, 17,736 (57.9%) were among MSM, including 15,953 (52.1%) cases among men who had sex with men only and 1,783 (5.8%) cases among men who had sex with both men and women (Figure 39). Overall, 4,548 (14.8%) cases were among MSW, 3,722 (12.1%) were among women, 4,601 (15.0%) were among men without information about sex of sex partner, and 37 (0.1%) were cases reported with unknown sex. Among the 22,284 male cases with information on sex of sex partner, 79.6% 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 2013–2017 (Figure 41). In these states, during 2016–2017, the number of cases increased 8.6% among MSM, 17.8% among MSW, and 24.9% among women.

Figure 39. Pie chart showing the distribution of primary and secondary syphilis cases in the United States in 2017 by sex and sexual behavior.

Figure 39. Primary and Secondary Syphilis — Distribution of Cases by Sex and Sexual Behavior, United States, 2017

Figure 40. Line graph showing rates of reported cases of primary and secondary syphilis in the United States from 1990 to 2017 by sex and male to female rate ratios.

Figure 40. Primary and Secondary Syphilis — Rates of Reported Cases by Sex and Male-to-Female Rate Ratios, United States, 1990–2017

Figure 41. Line graph showing reported cases of primary and secondary syphilis in 37 States from 2013 to 2017 by sex and sexual behavior.

Figure 41. Primary and Secondary Syphilis — Reported Cases by Sex and Sexual Behavior, 37 States, 2013–2017

Figure 42. Bar graph showing rates of reported cases of primary and secondary syphilis in the United States for men and women in 2017 by age group. Data provided in table 34.

Figure 42. Primary and Secondary Syphilis — Rates of Reported Cases by Age Group and Sex, United States, 2017

P&S Syphilis by Age

As in previous years, in 2017, rates of reported P&S syphilis cases were highest among persons aged 25–29 years (Figure 42, Table 34). In 2017, the highest rates were observed among men aged 25–29 years (51.9 cases per 100,000 males), 20–24 years (41.1 cases per 100,000 males), and 30–34 years (39.3 cases per 100,000 males). The highest rates among women were among those aged 20–24 years (7.8 cases per 100,000 females) and those aged 25–29 years (7.1 cases per 100,000 females).

During 2016–2017, the overall rate of reported P&S syphilis cases increased in all age groups among those aged 15 years or older (Table 34). Rates increased 9.8% among those aged 15–19 years, 7.8% among those aged 20–24 years, 10.7% among those aged 25–29 years, 14.3% among those aged 30–34 years, 17.8% among those aged 35–39 years, 6.4% among those aged 40–44 years, 4.3% among those aged 45–54 years, 11.8% among those aged 55–64 years, and 16.7% among those aged 65 or older.

In 2017, persons aged 15–44 years accounted for 80.2% of reported P&S syphilis cases with known age. Among men, during 2016–2017, the P&S syphilis rate increased in all age groups among those aged 15–44 years. Among women, the rate decreased slightly among those aged 15–19 years, but increased in all older age groups (Figures 43 and 44, Table 34).

Figure 43. Line graph showing United States rates of reported cases of primary and secondary syphilis among women aged 15 to 44 years from 2008 to 2017 by age group. Data for 2013 to 2017 provided in table 34.

Figure 43. Primary and Secondary Syphilis — Rates of Reported Cases Among Women Aged 15–44 Years by Age Group, United States, 2008–2017

Figure 44. Line graph showing United States rates of reported cases of primary and secondary syphilis among men aged 15 to 44 years from 2008 to 2017 by age group. Data for 2013 to 2017 provided in table 34.

Figure 44. Primary and Secondary Syphilis — Rates of Reported Cases Among Men Aged 15–44 Years by Age Group, United States, 2008–2017

P&S Syphilis by Race/Hispanic Ethnicity

In 2017, the rate of reported P&S syphilis cases was highest among Blacks (24.2 cases per 100,000 population) (Table 35B). The P&S syphilis rate among Blacks was 4.5 times the rate among Whites (5.4 cases per 100,000 population), the rate among Native Hawaiians/Other Pacific Islanders (NHOPI) (13.9 cases per 100,000 population) was 2.6 times the rate among Whites, the rate among Hispanics (11.8 cases per 100,000 population) was 2.2 times the rate among Whites, the rate among American Indians/Alaska Natives (AI/AN) (11.1 cases per 100,000 population) was 2.1 times the rate among Whites, and the rate among Asians (4.4 cases per 100,000 population) was 0.8 times the rate among Whites.

During 2013–2017, the P&S syphilis rate increased among all race/ Hispanic ethnicity groups (Figure 45). The greatest increases during 2016–2017 were observed among AI/AN (38.8%) and those who identified as Multiracial (31.7%), followed by Asians (15.7%), Whites (10.2%), NHOPI (9.4%), Hispanics (9.3%), and Blacks (5.7%).

More information on P&S syphilis rates among racial/Hispanic ethnicity 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 (Figure 46). Among 2017 P&S syphilis cases with known HIV status, 45.5% of cases among MSM were HIV-positive, compared with 8.8% of cases among MSW, and 4.5% of cases among women.

Figure 45. Line graph showing rates of reported cases of primary and secondary syphilis in the United States from 2013 to 2017 by race and Hispanic ethnicity. Data provided in table 35B.

Figure 45. Primary and Secondary Syphilis — Rates of Reported Cases by Race and Hispanic Ethnicity, United States, 2013–2017

Figure 46. Bar graph showing reported cases of primary and secondary syphilis in the United States in 2017 by sex, sexual behavior, and HIV status.

Figure 46. Primary and Secondary Syphilis — Reported Cases by Sex, Sexual Behavior, and HIV Status, United States, 2017

P&S Syphilis by Reporting Source

In 2017, 17.0% of P&S syphilis cases were reported from STD clinics, 71.7% were reported from venues outside of STD clinics, and 11.4% of cases had an unknown reporting source (Table A2). During 2016–2017, the number of P&S syphilis cases reported by STD clinics and by non-STD clinic settings increased (Figure 47). However, the proportion of P&S syphilis cases that were reported by STD clinics has declined over the last decade from 31.1% of cases in 2008 to 17.0% of cases in 2017. In 2017, private physicians/health maintenance organizations (HMOs) and STD clinics were the most common reporting sources among MSM (29.8% and 22.4%, respectively), MSW (23.0% and 19.8%, respectively), and women (26.1% and 14.4%, respectively) (Figure 48).

Figure 47. Line graph showing reported cases of primary and secondary syphilis in the United States from 2008 to 2017 by reporting source and sex.

Figure 47. Primary and Secondary Syphilis — Reported Cases by Reporting Source and Sex, United States, 2008–2017

Figure 48. Bar graph showing percentage of reported cases of primary and secondary syphilis in the United States in 2017 by sex, sexual behavior, and selected reporting sources.

Figure 48. Primary and Secondary Syphilis — Percentage of Reported Cases by Sex, Sexual Behavior, and Selected Reporting Sources, United States, 2017

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 since 2012 (Table 1). In 2017, there were a total of 918 reported cases of congenital syphilis, including 64 syphilitic stillbirths and 13 infant deaths, and the national rate was 23.3 cases per 100,000 live births. This rate represents a 43.8% increase relative to 2016 (16.2 cases per 100,000 live births) and a 153.3% increase relative to 2013 (9.2 cases per 100,000 live births). As has been observed historically, this increase in the congenital syphilis rate has paralleled increases in P&S syphilis among all women and reproductive aged women during 2013–2017 (155.6% and 142.8% increases, respectively) (Figure 49, Table 28).

During 2013–2017, 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 362.5% in the West, 107.7% in the South, 93.1% in the Northeast, and 43.8% in the Midwest (Table 41). During 2016–2017, the congenital syphilis rate increased 60.3% in the South, 40.7% in the West, 5.7% in the Northeast, and 5.7% in the Midwest. In 2017, the highest congenital syphilis rates were reported from the West (37.0 cases per 100,000 live births), followed by the South (29.5 cases per 100,000 live births), Midwest (9.2 cases per 100,000 live births), and the Northeast (5.6 cases per 100,000 live births). In addition, rates were highest among Blacks (58.9 cases per 100,000 live births), followed by AI/AN (35.5 cases per 100,000 live births), Hispanics (33.5 cases per 100,000 live births), Whites (9.7 cases per 100,000 live births), and Asians/Pacific Islanders (4.3 cases per 100,000 live births) (Table 42).

Figure 49. Bar graph showing reported cases of congenital syphilis by year of birth and rates of reported cases of primary and secondary syphilis among women aged 15 to 44 years in the United States from 2008 to 2017. Data for congenital syphilis cases from 2008 to 2017 provided in table 1 and for primary and secondary syphilis among women from 2013 to 2017 provided in table 31.

Figure 49. Congenital Syphilis — Reported Cases by Year of Birth and Rates of Reported Cases of Primary and Secondary Syphilis Among Women Aged 15–44 Years, United States, 2008–2017

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

In 2017, the total case count of reported syphilis (all stages combined: P&S, early latent, late and late latent, and congenital) was the highest recorded since 1993. The total number of cases of syphilis (all stages) reported to CDC increased 15.3% during 2016–2017 (from 88,053 cases to 101,567 cases) (Table 1). The number of cases of early latent syphilis reported to CDC increased 17.6% (from 28,924 cases to 34,013 cases), and the number of cases of late and late latent syphilis increased 17.3% (from 30,676 cases to 35,992 cases) (Tables 1, 36, and 38).

Syphilis among Special Populations

More information about syphilis and congenital syphilis in racial/Hispanic ethnicity 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, in the last five years, rates have increased among both men and women, and the P&S syphilis rate among women has more than doubled. Rates of reported congenital syphilis cases also increased substantially during 2013–2017 and during 2016–2017. MSM continued to account for the majority of reported P&S syphilis cases in 2017. Nationally, the highest rates of P&S syphilis in 2017 were observed among men aged 20–34 years, among men in the West, and among Black men.

References

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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(15):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(1):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. de Voux A, Kidd S, Grey JA, et al. State-specific rates of primary and secondary syphilis among men who have sex with men — United States, 2015. MMWR Morb Mortal Wkly Rep 2017; 66(13):349–354.

6. Peterman TA, Kahn RH, Ciesielski CA, et al. Misclassification of the stages of syphilis: implications for surveillance. Sex Transm Dis 2005; 32(3):144–149.

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