Cases of the sexually transmitted disease, once almost eliminated in the United States, have more than doubled among gay and bisexual men since the year 2000, according to the U.S. Centers for Disease Control and Prevention.
Based on data from the National Notifiable Diseases Surveillance System reported as of April 28, 2014, U.S. health officials found there were 5.3 cases of primary and secondary syphilis per 100,000 people in 2013 compared to 2.1 cases per 100,000 in 2000.
From 2005 to 2013, the rates increased the most among men of all ages and races/ethnicities across all regions of the United States. And in recent years, the largest increases have occurred among gay, bisexual, and other men who have sex with men, according to the report published May 9 in the CDC's Morbidity and Mortality Weekly Report.
"We are very concerned about what we consider this rising epidemic of syphilis among gay and bisexual men," said Dr. Gail Bolan, director of the CDC's division of STD prevention. "This is a consistent, disturbing trend."
In 2000, the year with the fewest cases of syphilis, there were 6,000 cases nationwide. "This was an all-time low, and the vast majority of cases were among heterosexuals," Bolan said.
In 2012, there were almost 9,000 cases of syphilis, and 84 percent of them were among gay and bisexual men, Bolan noted. "We are talking about cases more than doubling," she added.
In 2013, there were more than 16,000 cases of syphilis, 91 percent of these in men. "We haven't seen case numbers like that since back in the '90s," Bolan said.
Bolan isn't sure why syphilis is making a resurgence. "We think it's a mix of social and individual factors, but we need more information to know why," she said.
Fighting syphilis is particularly difficult because it is only contagious during the brief time symptoms appear. To stem the tide of most sexually transmitted diseases, patients are asked about their partners so they can be identified and tested.
With syphilis, however, many of these men don't know their partners, Bolan said. "We have about three weeks to find the partners and get them treated before they transmit it to someone else," she explained.
In addition, many young doctors don't recognize syphilis so they might not treat it, Bolan pointed out. "When they see a little sore on the genitals, they think herpes and do not realize that this is a case of syphilis that needs to be treated that day," she said.
Bolan believes that, given this epidemic, any man with a genital sore should be given antibiotics, even if it turns out not to be syphilis.
"Gay and bisexual men need to be aware that syphilis is common in their communities," Bolan said. "We are encouraging these men that if they engage in high-risk behaviors -- lots of anonymous partners, using drugs that lead to high-risk behaviors -- they should be checked for syphilis every three months."
In general, gay and bisexual men should be screened for syphilis every year, Bolan added.
To protect themselves, she said, men should use condoms, reduce their number of partners, or in some cases, abstain from sex.
Syphilis usually appears first as a painless genital sore, which disappears without a scar, or it can appear in the back of the throat and be missed entirely, according to Dr. Demetre Daskalakis, an infectious disease expert at Mount Sinai Hospital in New York City.
After two or three months, some people get secondary syphilis, which can appear in many ways, but commonly begins as a rash on the soles of the feet and palms of the hands, and could include fever, swollen lymph nodes and a sore throat, Daskalakis said.
"That also goes away, and if not tested for syphilis, can go on to the long-term complications," he added.
Daskalakis noted that syphilis can be transmitted through oral sex as well as through vaginal or anal sex, so a condom may not be protective in all cases. A lot of gay and bisexual men, particularly those with HIV, aren't using condoms consistently and are at risk of transmitting and contracting syphilis, he said.
"Some people are avoiding anal sex because of the HIV risk and are having oral sex and not using condoms -- very few people use condoms for oral sex. That's an efficient mechanism for syphilis transmission," Daskalakis said.
He noted that syphilis increases the risk for getting and transmitting HIV and, if untreated, can lead to stroke, heart disease and mental problems, including dementia.
Treatment is simple, he added: Penicillin.
For more on syphilis, visit the U.S. Centers for Disease Control and Prevention.