Syphilis is on the rise among gay and bisexual men, according to a federal study released this week by the Centers for Disease Control and Prevention. From 2005 to 2013, the number of syphilis cases reported nearly doubled, from 8,724 to 16,663, with the majority of patients being men who have sex with other men.

The study also found black men were five times as likely to contract the disease as white men, and black women 13 times more at risk than white women, though men account for 91% of current cases.

Syphilis—which can lead to blindness, dementia and (in rare cases) death if left untreated—is caused by the bacteria T. pallidum. It wreaked havoc for centuries before the advent of penicillin, but was  nearly eliminated in the United States more than a decade ago. This uptick is public-health concern, say researchers, because it indicates unsafe sex practices that could increase exposure to HIV.  (There's also concern about the emergence of antibiotic-resistent strains of syphilis.

It's technically a notifiable disease, which means health-care providers are required to notify public-health authorities about confirmed cases, and provide notification to an infected person's sexual partners.

“We’ve got to re-evaluate and look at new approaches that we can use to drive these rates down,”  said Gail Bolan, director of the CDC's Division of STD Prevention. Recommendations include using latex condoms, limiting sex partners and encouraging monogamous relationships.  The CDC also recommends men who have sex with men get tested at least once a year.