Just 14 short years ago, the sexually transmitted infection, syphilis, was on the verge of elimination in the United States; however, that trend has turned around dramatically as “The Great Imitator” has made a huge comeback by more than doubling since 2005.

Darkfield microscopy of T. pallidum/CDC
Darkfield microscopy of T. pallidum/CDC

The resurgence in the spirochetal infection is mainly due to a rise in cases in Men who have sex with men, aka MSM, according to the newest data published by Centers for Disease Control and Prevention (CDC) researchers in this week’s Morbidity and Mortality Weekly Report (MMWR).

The report notes, during the time frame of  2005–2013, the number of primary and secondary syphilis cases reported each year in the United States nearly doubled, from 8,724 to 16,663; the annual rate increased from 2.9 to 5.3 cases per 100,000 population.  91 percent of the cases were in men.

In 2012, primary and secondary syphilis cases in the 35 reporting areas ( 34 states and the District of Columbia) that reported the sex of sex partners for ≥70% of male cases comprised 83.7% (13,113) of all nationwide cases. In those areas, the proportion of male primary and secondary syphilis cases attributed to MSM increased from 77.0% (6,366) in 2009 to 83.9% (8,701) in 2012. 

Geographically in 2013, the West region of the US had the highest rates of syphilis (6.5 cases per 100,000 population), with the report stating that 2013 was the first time in 50 years that the South region did not have the highest overall syphilis rate among regions. For more infectious disease news and information, visit and “like” the Infectious Disease News Facebook page.

The CDC team says the increase in syphilis among MSM is a major public health concern, particularly because syphilis and the behaviors associated with acquiring it increase the likelihood of acquiring and transmitting human immunodeficiency virus (HIV). There are reported rates of 50%70% HIV coinfection among MSM infected with primary and secondary syphilis and high HIV seroconversion rates following primary and secondary syphilis infection. 

Related: Guatemalan syphilis experiment: in the name of public health?

CDC, in collaboration with state and local partners, health-care providers, and MSM-oriented organizations, is also engaged in research to better understand risk factors for syphilis among MSM, develop improved care models to better reach and serve MSM populations, assess whether MSM are being tested and treated appropriately, and determine what barriers exist in the diagnosis and treatment of syphilis among MSM.

Syphilis is a sexually transmitted infection (STI) caused by the bacterium, Treponema pallidum. The most common way to get syphilis is by having sexual contact (oral, genital or anal) with an infected person. The secondary lesions are also infective and contact with them could transmit the bacteria. It can also be transmitted from an infected mother to her baby (congenital transmission).