Majority of US syphilis cases are now in gay men

Almost two-thirds of syphilis cases in the United States in 2003 were in gay men and other men who have sex with men, according to a study published in the June edition of the American Journal of Public Health. A fall in the incidence of syphilis of over 50% amongst heterosexual men and women between 2000 and 2003 was more than offset by a significant increase in the incidence of the infection amongst men who have sex with men.

Syphilis causes genital ulcers and can facilitate the transmission and acquisition of HIV infection. It can also act as a marker for risky sexual activity, although the infection can be readily transmitted during sexual activities, such as oral sex, which do not involve a significant risk of HIV transmission.

During the 1980s, there was a 54% increase in the incidence of primary and secondary syphilis in the United States, with African-Americans disproportionately affected by the disease. It is thought that the increase in syphilis during the 1980s was tied to the increasing use of crack cocaine and prostitution by some users to fund their habit. By the mid-1990s, however, the incidence of syphilis in the US had fallen sharply, and in 1999 a national syphilis elimination plan was published.

This trend has since reversed, with an increase in every year since 2001 in the incidence of primary and secondary syphilis. The US is not alone in experiencing a re-emergence of the infection, with outbreaks of syphilis reported across the UK and Europe, often focused on gay men, since the late 1990s.

Investigators therefore used data provided from each of the US states and 63 large American cities to analyse trends in syphilis from 1990 to 2003. They paid particular attention to the re-emergence of the infection amongst gay men since the late 1990s.

Between 1990 and 2003 there was an overall fall of 88% in the incidence of syphilis in the US. During this period, rates of the infection fell for all racial groups, with the most notable decline occurring in African-Americans (95%), with smaller falls observed amongst whites (42%).

Thanks to continual falls in the incidence of the infection through the 1990s, fewer cases of syphilis were recorded in the US in 2000 than in any year since 1941 when surveillance started.

This trend was reversed, however, between 2000 and 2003 when a 19% increase in the incidence of the infection was recorded. When the investigators analysed these data in more detail they noted that new cases of the infection continued to decline amongst women, but were increasing amongst men. Indeed, after 2000 the incidence of syphilis increased by 62% in men, with increases observed in all racial groups with the exception of African-Americans, with particularly sharp increases seen amongst white men.

Of the 2424 cases of syphilis seen in men between 2000 and 2003, 2,085 (86%) were in white men.

The investigators also noted a shift in the geographical distribution of the infection. Although rates of syphilis fell by 20% in the Midwest and 16% in the South, they increased by 300% in Northeastern states and by 170% in the West.

Syphilis became particularly well established in urban centres in the period after 2000, with 52 of the 63 (82%) cities contributing data showing evidence of an increased incidence. Men were significantly more likely than women to be diagnosed with the infection in these cities.

The investigators calculated that in 2000 only 441 cases of syphilis were diagnosed in gay men. By 2003, however, this had increased to 4,387 cases, representing 62% of all syphilis cases in the US. Yet, between 2000 and 2003, the investigators calculate that there was a 50% decrease in syphilis incidence amongst heterosexual men and women.

“Syphilis cases among MSM rose sharply after 2000, accounting for the overall increase in syphilis during 2000 through 2003”, write the investigators, who note simultaneous outbreaks of the infection amongst gay men in Europe and Europe. They therefore comment, “these coincident outbreaks among MSM suggest that substantial and concurrent changes in sexual behaviour have facilitated syphilis transmission in many industrialized countries.”

They note that in 2006 a revised syphilis eradication plan, specifically mentioning gay men, was published in the US. Traditional measures of syphilis control, most notably contract tracing, have proved less effective for men who have sex with men. Key recommendations to controlling the infection in gay men included in the plan therefore include:

• Gathering robust data about the incidence the infection in men who have sex with men.
• Using the internet to engage men who have sex with men and to facilitate partner notification.
• Enhanced syphilis education in the community and in sexual health clinics.
• The use of outreach to improve awareness of the infection.
• Improving access to syphilis testing.

The investigators conclude “mobilizing the MSM community to take an active role in these efforts is crucial for their success.”