In 2015, the rate of reported primary and secondary syphilis in the United States
was 7.5 cases per 100,000 population, nearly four times the previous lowest documented
rate of 2.1 in 2000 (
1
). In 2015, 81.7% of male primary and secondary syphilis cases with information on
the sex of the sex partner were among gay, bisexual, and other men who have sex with
men (collectively referred to as MSM) (
1
). These data suggest a disproportionate incidence of disease among MSM. However,
attempts to quantify this disparity have been hindered by limited data on the size
of the MSM population at the state level. To produce the first estimates of state-specific
rates of primary and secondary syphilis among MSM, CDC used MSM population estimates
based on a new methodology (
2
) and primary and secondary syphilis case counts reported in 2015 to the National
Notifiable Diseases Surveillance System. Among 44 states reporting information on
the sex of sex partners for ≥70% of male cases, the overall rate of primary and secondary
syphilis among all men (aged ≥18 years) in the United States in 2015 was 17.5 per
100,000, compared with 309.0 among MSM and 2.9 among men who reported sex with women
only. The overall rate of primary and secondary syphilis among MSM was 106.0 times
the rate among men who have sex with women only and 167.5 times the rate among women.*
These data highlight the disproportionate impact of syphilis among MSM and underscore
the need for innovative and targeted syphilis prevention measures at the state and
local level, especially among MSM. It is important that health care providers recognize
the signs and symptoms of syphilis, screen sexually active MSM for syphilis at least
annually, and provide timely treatment according to national sexually transmitted
diseases treatment guidelines (
3
).
Case reports of primary and secondary syphilis cases for MSM, men who have sex with
women only, and women were obtained from national data reported regularly by all states
for 2015. These data include limited demographic and clinical information, including
the sex of sex partners. Population estimates of the number of MSM by state were obtained
using new methodology that makes use of census and population-based survey data (
2
). To estimate the MSM population size, the estimated percentage of MSM among men
was adjusted (
4
) according to each U.S. county’s percentage of households with a male head and a
male partner, obtained from American Community Survey summary data and urban-rural
classification (large central metropolitan, large fringe metropolitan, medium or small
metropolitan, or nonmetropolitan or rural) from the National Center for Health Statistics
(
4
). The county’s percentage of MSM was adjusted according to the ratio of its percentage
of male same-sex households to the overall percentage among all counties at the same
urban-rural classification, which was then multiplied by the number of men in the
county to achieve the estimated MSM population size. This final number was then scaled
to equal 3.9% of the adult male population, based on a prior national MSM estimate
(
5
).
To optimize stability of the estimates, the analysis was limited to the 44 states
that included sex of sex partner in ≥70% of male primary and secondary syphilis case
reports for 2015. The 70% threshold represented the best balance between including
male cases of primary and secondary syphilis while gathering the most complete epidemiologic
data for those cases. State-specific rates of primary and secondary syphilis among
MSM were compared with rates of primary and secondary syphilis among men who have
sex with women only and also among women (cases in men with unknown sex of sex partner
were excluded from this analysis). Rate ratios were calculated as 1) the rate of primary
and secondary syphilis among MSM divided by the rate among men who have sex with women
only and 2) the rate among MSM divided by the rate among women.
†
Primary and secondary syphilis cases in the 44 states included in the analysis accounted
for 83.4% of all 23,872 reported primary and secondary syphilis cases in the United
States in 2015. Among the reported primary and secondary syphilis cases among men
and women in these 44 states in 2015, 12,118 (60.8%) were among MSM, including 10,942
(54.9%) among men who had sex with men only and 1,176 (5.9%) cases among men who had
sex with both men and women.
Among the 44 states, the overall rates of primary and secondary syphilis in 2015 among
all men, MSM, men who have sex with women only, and women were 17.5, 309.0, 2.9, and
1.8 cases per 100,000 population, respectively. State-specific rates among MSM ranged
from 73.1 per 100,000 population (Alaska) to 748.3 (North Carolina) (Table 1). The
overall U.S. rate of primary and secondary syphilis among MSM was 106.0 times the
rate among men who have sex with women only, with state-specific rate ratios ranging
from 39.2 (Minnesota) to 342.1 (Hawaii). The overall rate of primary and secondary
syphilis among MSM was 167.5 times the rate among women, with state-specific rate
ratios ranging from 63.7 (Louisiana) to 2,140.3 (Hawaii).
TABLE 1
Rates and rate ratios for primary and secondary syphilis among men who have sex with
men (MSM), among men who have sex with women only, and among women, by state and overall
— United States, 2015*
State†
MSM
Rate of primary and secondary syphilis per 100,000 population
Rate ratio§
Estimated no. in population
% of all men
MSM
Men who have sex with women only
Women
MSM compared with men who have sex with women only
MSM compared with women
Overall
3,921,515
3.8
309.0
2.9
1.8
106.0
167.5
Alabama
41,822
2.3
320.4
2.4
1.9
131.5
169.4
Alaska
5,469
1.9
73.1
1.1
0.4
67.8
189.5
Arizona
112,102
4.5
385.4
3.3
1.7
116.1
222.0
Arkansas
19,101
1.7
314.1
3.4
2.2
92.9
140.6
California
796,926
5.5
332.2
3.9
3.1
85.8
108.0
Colorado
74,742
3.6
248.9
1.2
0.2
205.5
1,023.7
Connecticut
43,542
3.2
112.5
0.7
1.0
162.7
117.6
Florida
351,797
4.6
370.1
4.5
2.4
82.7
152.3
Hawaii
15,707
2.8
388.4
1.1
0.2
342.1
2,140.3
Idaho
9,979
1.7
320.7
2.4
1.3
131.0
242.7
Illinois
199,075
4.1
311.9
2.5
1.5
124.6
203.8
Indiana
72,413
3.0
290.0
1.5
1.1
193.3
266.6
Iowa
20,924
1.8
219.8
1.0
0.4
226.7
531.7
Kansas
21,906
2.0
228.2
1.3
1.4
169.6
168.1
Kentucky
47,576
2.9
159.7
1.9
1.3
84.5
126.8
Louisiana
43,204
2.5
601.8
8.4
9.5
71.9
63.7
Maine
14,375
2.8
118.3
0.4
1.1
295.3
108.9
Maryland
83,668
3.8
325.1
4.5
2.4
72.0
137.9
Massachusetts
110,254
4.3
278.4
1.1
0.9
247.3
324.2
Michigan
116,354
3.1
233.8
1.4
0.8
163.8
280.2
Minnesota
82,510
4.0
147.9
3.8
1.7
39.2
87.0
Mississippi
20,184
1.9
658.9
4.1
2.6
161.0
251.3
Missouri
72,875
3.2
204.5
3.8
2.2
53.9
93.0
Montana
6,800
1.7
132.4
0.5
0.0
254.1
—¶
Nevada
51,990
4.8
398.2
4.9
1.8
81.3
216.6
New Hampshire
13,868
2.7
187.5
1.2
0.6
155.3
337.8
New Jersey
136,271
4.1
152.6
1.3
0.7
117.2
219.3
New Mexico
18,675
2.4
428.4
2.5
1.4
169.2
314.0
North Carolina
105,707
2.9
748.3
5.3
2.7
140.0
278.2
North Dakota
4,840
1.7
165.3
1.1
0.0
150.4
—
Ohio
146,033
3.4
214.3
2.9
1.4
73.3
157.5
Oklahoma
37,006
2.6
418.9
2.3
1.4
185.4
297.6
Oregon
60,932
4.0
313.5
2.8
2.2
111.9
142.1
Pennsylvania
162,848
3.3
256.1
1.6
0.8
159.3
310.5
Rhode Island
24,745
6.1
226.3
2.7
0.9
84.6
248.9
South Carolina
35,388
2.0
536.9
2.9
1.7
187.8
307.9
South Dakota
4,937
1.5
405.1
2.6
2.2
156.2
186.2
Tennessee
73,460
3.0
325.3
2.8
0.9
115.4
371.3
Texas
378,310
3.9
289.4
3.2
2.2
90.1
133.9
Utah
33,898
3.3
132.8
0.5
0.2
251.1
679.2
Vermont
7,142
2.9
126.0
0.0
0.0
—
—
Virginia
115,515
3.7
210.4
1.5
0.5
138.3
436.0
Washington
113,504
4.2
306.6
1.9
1.1
160.6
290.6
West Virginia
13,141
1.8
197.9
2.3
1.2
87.2
165.0
* Data based on 2015 cases reported to CDC by June 8, 2016.
† To optimize stability of the estimates, the analysis was limited to the 44 states
that included sex of sex partner in ≥70% of male primary and secondary syphilis case
reports for 2015.
§ Rate ratios were calculated as 1) the rate of primary and secondary syphilis among
MSM divided by the rate among men who have sex with women only and 2) the rate among
MSM divided by the rate among women. In this report “women” is used to describe both
females aged ≥18 years (used for calculating rates for women), and females of unknown
ages (used for calculating rates for men who had sex with women only). Rate ratios
were rounded to tenths.
¶ Montana, North Dakota, and Vermont had no cases of primary and secondary syphilis
reported among women for 2015, resulting in an undefined rate ratio comparing MSM
with women. Vermont had no cases of primary and secondary syphilis reported among
men who had sex with women only in 2015, resulting in an undefined rate ratio comparing
MSM with men who have sex with women only..
Rates of primary and secondary syphilis among MSM varied by U.S. Census region and
by state, with the highest rates in the South and West. Four of the five states with
the highest primary and secondary syphilis rates among MSM were southern states (Louisiana,
Mississippi, North Carolina, and South Carolina) (Table 2). Among states with the
10 highest rates of primary and secondary syphilis in the United States in 2015 (
1
), five states (Arizona, Louisiana, Mississippi, Nevada, and North Carolina) also
ranked among the top 10 states with the highest rates of primary and secondary syphilis
among MSM (Table 2).
TABLE 2
States ranked from highest to lowest, by rates of primary and secondary syphilis cases
overall and among men who have sex with men (MSM) and men who have sex with women
only, and by rate ratios comparing the rates for MSM with the rates for men who have
sex with women only and the rates for women — United States, 2015*
Rank†
Rate of primary and secondary syphilis per 100,000 population
Rate ratio§
Overall primary and secondary syphilis
Primary and secondary syphilis among MSM
Primary and secondary syphilis among men who have sex with women only
MSM compared with men who have sex with women only
MSM compared with women
1
Louisiana
North Carolina
Louisiana
Hawaii
Hawaii
2
California
Mississippi
North Carolina
Maine
Colorado
3
North Carolina
Louisiana
Nevada
Montana
Utah
4
Nevada
South Carolina
Maryland
Utah
Iowa
5
Florida
New Mexico
Florida
Massachusetts
Virginia
6
Arizona
Oklahoma
Mississippi
Iowa
Tennessee
7
Oregon
South Dakota
California
Colorado
New Hampshire
8
Maryland
Nevada
Missouri
Indiana
Massachusetts
9
Illinois
Hawaii
Minnesota
South Carolina
New Mexico
10
Mississippi
Arizona
Arkansas
Oklahoma
Pennsylvania
11
Rhode Island
Florida
Arizona
Kansas
South Carolina
12
Hawaii
California
Texas
New Mexico
Oklahoma
13
Washington
Tennessee
Ohio
Michigan
Washington
14
Texas
Maryland
South Carolina
Connecticut
Michigan
15
Massachusetts
Idaho
Tennessee
Mississippi
North Carolina
16
South Carolina
Alabama
Oregon
Washington
Indiana
17
Alabama
Arkansas
Rhode Island
Pennsylvania
Mississippi
18
New Mexico
Oregon
South Dakota
South Dakota
Rhode Island
19
Oklahoma
Illinois
New Mexico
New Hampshire
Idaho
20
Tennessee
Washington
Illinois
North Dakota
Arizona
21
Pennsylvania
Indiana
Idaho
North Carolina
New Jersey
22
Missouri
Texas
Alabama
Virginia
Nevada
23
Ohio
Massachusetts
West Virginia
Alabama
Illinois
24
Colorado
Pennsylvania
Oklahoma
Idaho
Alaska
25
South Dakota
Colorado
Washington
Illinois
South Dakota
26
Arkansas
Michigan
Kentucky
New Jersey
Alabama
27
Minnesota
Kansas
Pennsylvania
Arizona
Kansas
28
Indiana
Rhode Island
Virginia
Tennessee
West Virginia
29
New Jersey
Iowa
Indiana
Oregon
Ohio
30
Michigan
Ohio
Michigan
Arkansas
Florida
31
Virginia
Virginia
Kansas
Texas
Oregon
32
Idaho
Missouri
New Jersey
West Virginia
Arkansas
33
Kentucky
West Virginia
Colorado
California
Maryland
34
New Hampshire
New Hampshire
New Hampshire
Rhode Island
Texas
35
Kansas
North Dakota
Hawaii
Kentucky
Kentucky
36
West Virginia
Kentucky
Massachusetts
Florida
Connecticut
37
Connecticut
New Jersey
North Dakota
Nevada
Maine
38
Iowa
Minnesota
Alaska
Ohio
California
39
Utah
Utah
Iowa
Maryland
Missouri
40
Maine
Montana
Connecticut
Louisiana
Minnesota
41
North Dakota
Vermont
Utah
Alaska
Louisiana
42
Vermont
Maine
Montana
Missouri
—¶
43
Montana
Connecticut
Maine
Minnesota
—
44
Alaska
Alaska
Vermont
—
—
* Data based on 2015 cases reported to CDC by June 8, 2016.
† To optimize stability of the estimates, the analysis was limited to the 44 states
that included the sex of sex partners in ≥70% of male primary and secondary syphilis
case reports for 2015.
§ Rate ratios were calculated as 1) the rate of primary and secondary syphilis among
MSM divided by the rate among men who have sex with women only and 2) the rate among
MSM divided by the rate among women. In this report “women” is used to describe both
females aged ≥18 years (used for calculating rates for women), and females of unknown
ages (used for calculating rates for men who had sex with women only).
¶ Montana, North Dakota, and Vermont had no cases of primary and secondary syphilis
reported among women for 2015, resulting in an undefined rate ratio comparing MSM
with women. Vermont had no cases of primary and secondary syphilis reported among
men who had sex with women only in 2015, resulting in an undefined rate ratio comparing
MSM with men who have sex with women only..
Discussion
These are the first state-specific rates of primary and secondary syphilis reported
for MSM in the United States. The lowest state-specific MSM primary and secondary
syphilis rate (73.1 in Alaska) exceeded the highest overall U.S. primary and secondary
syphilis rate (70.9), which was observed in 1946. In every state, the incidence of
reported syphilis among MSM was higher than the incidence among men who have sex with
women only, with rate ratios ranging from 39.2 to 342.1. These data support CDC’s
earlier findings using national population size estimates, which highlighted national
disparities in syphilis incidence. In the earlier findings, the rate of syphilis incidence
among MSM was estimated to be 154 per 100,000 population, compared with 2.2 per 100,000
among other men, resulting in a rate ratio of 71 (
5
), in comparison to the estimate of 106.0 in the current analysis. However, the previous
findings were limited in their applicability to state or local areas because the percentage
of adult males who are MSM varies widely among states.
Although state-specific incidence rates varied, even in low incidence states (e.g.,
North Dakota), syphilis rates among MSM were higher than those among men who have
sex with women only. The geographic variation highlights the importance of these data
for state and local health departments, which can use these data to better understand
their local syphilis epidemiology and target resources and interventions to address
disparities between MSM and other population groups. The comparison of state-specific
rates also highlights the high disease incidence in the South. Four of the five states
with the highest primary and secondary syphilis incidence rates among MSM in 2015
were southern states. The estimates of state-specific rates among men who have sex
with women only, although lower than those among MSM, also have implications for the
rates of syphilis among women. Trends in congenital syphilis tend to follow trends
in the incidence of primary and secondary syphilis among women of reproductive age,
which has been increasing recently (
6
). Congenital syphilis can result in serious health consequences in infants (
6
). Although CDC is limited by its data usage agreement with the Council of State and
Territorial Epidemiologists to conduct data analysis at the state level (
7
), further analyses at the county level by state and local health jurisdictions could
be helpful to inform public health action by elucidating geographic disparities in
greater detail.
The findings in this report are subject to at least four limitations. First, analyses
were restricted to states where the sex of sex partners (male, female, or both) was
reported for ≥70% of male cases of primary and secondary syphilis cases during 2015.
Although 83.4% of all reported primary and secondary syphilis reported in the United
States during 2015 were included, these jurisdictions might not be representative
of all persons who receive a diagnosis of primary and secondary syphilis. Second,
the denominators used in calculating the rates of primary and secondary syphilis were
estimates of the number of MSM in each state, based on the reporting of same-sex households
in the American Community Survey; underreporting of same-sex households could result
in an underestimation of the MSM population and an overestimation of primary and secondary
syphilis rates. Third, cases of syphilis in men for whom the sex of sex partners was
unknown were excluded in calculations for both MSM and men who have sex with women
only. If MSM are more likely to underreport the sex of their sex partner, this might
result in an underestimation of the rate of syphilis among MSM and consequent rate
ratio when comparing syphilis rates among MSM and men who have sex with women only.
Improving the quality of case report data regarding sex of sex partner information
could increase the awareness of public health officials regarding the characteristics
of syphilis within their communities. Finally, primary and secondary syphilis case
report data likely underestimate the actual number of incident syphilis infections
in the United States because not all infections are diagnosed and reported (
8
).
Despite these limitations, these findings are consistent with previous reports that
showed pronounced disparities in primary and secondary syphilis rates between MSM
and men who have sex with women only (
5
), and the use of state-specific MSM population sizes and primary and secondary syphilis
case counts permits comparison of primary and secondary syphilis rates by state. Rates
among MSM compared with men who have sex with women only were higher in every state,
but state-specific data suggested that certain states might have a greater need for
syphilis prevention. Because MSM represent the majority of all primary and secondary
syphilis cases, the success of syphilis prevention programs is contingent upon addressing
the high rates of syphilis among MSM. It is important that both private and public
health care providers 1) recognize the signs and symptoms of syphilis, 2) conduct
a comprehensive sexual history, 3) screen all sexually active MSM for syphilis at
least annually, and 4) provide timely treatment according to national sexually transmitted
diseases treatment guidelines (
3
). Part of this sexual history includes eliciting information on sexual practices
and the sex of patients’ sex partners.
§
Summary
What is already known about this topic?
Syphilis rates in the United States have been steadily increasing since 2001, and
gay, bisexual, and other men who have sex with men (collectively referred to as MSM)
represent a disproportionate number of cases. In the absence of reliable, state-specific
denominators it has been difficult to estimate state-specific rates and rate ratios
to accurately measure the geographic variation and disparity.
What is added by this report?
State-specific rate ratios comparing the rate of syphilis among MSM with the rate
among men reporting sex with women only ranged from 39.2 (Minnesota) to 342.1 (Hawaii);
overall, MSM had a rate of primary and secondary syphilis 106.0 times the rate among
men who reported sex with women only.
What are the implications for public health practice?
These state-specific rates further highlight the disproportionate impact of syphilis
among MSM. Providers should screen sexually active MSM for syphilis at least annually
and provide timely treatment according to national sexually transmitted diseases treatment
guidelines.