Analysis Reports Significant Increases in Incident Rates of Syphilis Among U.S. Service Members

The crude annual incidence rates for syphilis among U.S. service members rose 49.1 percent over a health surveillance period from 2010 to 2014, according to a new analysis published in the September issue of the Medical Surveillance Monthly Report from the Armed Forces Health Surveillance Center (AFHSC).

During the surveillance period of January 1, 2010 through August 31, 2015, a total of 2,976 cases of syphilis were diagnosed. The annual incidence rates increased from 30.9 cases per 100,000 person-years (p-yrs) in 2010 to 46.1 cases per 100,000 p-yrs in 2014. In the first 8 months of 2015, the rate was 47.4, the highest level during the surveillance period, the report said.

“The increasing incidence of syphilis in military members is of significant public health concern because this finding suggests that some service members have been engaging in unsafe sexual practices that increase the likelihood of acquisition of other sexually transmitted infections (including HIV),” according to the authors’ conclusions.

Syphilis is a highly contagious, systemic infectious disease caused by the bacterium Treponema pallidum, and is transmitted primarily through sexual or other physically intimate contact; transmission requires direct contact with a syphilitic sore. In the U.S. civilian population, rates of reported cases of primary and secondary syphilis in males increased 91 percent from 2005 to 2013.

Among all beneficiaries of the Military Health System, reported syphilis cases have increased since 2012. In July 2105, the number of reported syphilis cases in the preceding 12 months was higher than any similar 12-month period in the previous five years, according to the Department of Defense AFHSC Reportable Events Monthly Report.

In the new analysis, of the 2,976 cases of syphilis diagnosed, 51 percent (n=1,523) were identified through a reportable medical event for syphilis, while another 45.6 percent (n=1,357) were identified via a diagnosis in an outpatient record. Sixty cases (2.0 percent) and 36 cases (1.2 percent) were identified via records in the Theater Medical Data Store or by discharge diagnoses in inpatient records, respectively.

Forty-two percent (n=1,253) of cases were specifically identified as primary or secondary syphilis; crude incidence rates of primary and secondary syphilis cases increased every year since 2011. Syphilis cases staged as latent accounted for an additional 27.1 percent (n=809) of cases; cases where the stage was unspecified comprised another 670 (22.5 percent) cases. Crude rates of latent and unspecified syphilis peaked during 2013 and 2014, respectively, while late syphilis rates in 2015 were slightly lower than the rates in the first year of the surveillance period.

Men contributed the greatest proportion of syphilis cases (88.7 percent) during the period, and incidence rates for males increased every year of the surveillance period. Female rates of syphilis were highest in 2014 at 34.0 cases per 100,000 p-yrs.

Overall, syphilis rates were highest in those service members aged 20–29 years; these age groups accounted for 61.6 percent of the total number of cases ascertained. These age groups have also demonstrated consistent increases in incidence rates year after year during the surveillance period.

The overall incidence rate in black, non-Hispanic service members was twice that of Hispanics, who had the second highest overall incidence rate of syphilis (Table 2). Almost one-quarter of syphilis cases (24.4 percent; 727 cases) also were diagnosed as HIV seropositive; of these, 601 (20.2 percent) were diagnosed before they became a syphilis case and the remainder (4.2 percent) were diagnosed as HIV seropositive after syphilis diagnosis.

As the authors’ conclusions noted, there have been multiple hypotheses for the resurgence of syphilis in the civilian population: among these are decreases in safer sex practices; increased use of the Internet as a means of meeting sexual partners; and the increase of harm reduction strategies such as oral sex, which can decrease the risk of HIV transmission but conversely increase the risk of contracting syphilis. Several of these sexual risk behaviors have been documented as being increased in Army service members who are HIV seroconverters.

“Developing and implementing syphilis prevention measures targeting service members at high risk of acquisition should continue to be promoted as well as continuation of aggressive sexual partner notification programs,” the study concluded.

Source: Armed Forces Health Surveillance Center (AFHSC)