A spike in syphilis infections is being fueled by gay and bisexual men across the U.S., who now account for 75 percent of reported cases, federal health officials say.

The rise in syphilis among gay men continues a trend the CDC says started in 2000, when cases attributed to gay men spiked from 7 percent of total cases to 64 percent in 2004. By 2013, men who have sex men accounted for 75 percent of 17,375 reported syphilis cases, the highest overall number of syphilis cases since 1995. The CDC announced the findings last week.

“We’re concerned about this increase,” Gail Bolan, director of the CDC’s division of sexually transmitted disease prevention, tells Reuters. ”The traditional tools we have been using do not seem to be as effective.”

In Georgia, the syphilis rate of 10.3 cases per 100,000 people is nearly twice the national average of 5.5 and second only to Washington, D.C.'s rate of 26.6. In Texas, the rate is 5.7 cases per 100,000 people.

Among counties, Los Angeles led the national in reported syphilis cases in 2013 with 1,095, followed by Cook County, Ill., with 694 and San Francisco with 503. Fulton County, Ga., ranked 6th with 379 while Harris County, Texas, ranked 8th with 319 cases.

In Georgia, other counties included Cobb (59th with 59 cases), Clayton (67th with 50) and Gwinnett (68th with 50). Other Texas counties include Tarrant (27th with 153 cases), Travis (35th with 128)

The CDC says that higher numbers of lifetime sex partners, higher rates of partner change and unprotected sex contributes to the higher rate of syphilis among gay and bisexual men. Other factors, including HIV among gay men and lower economic status and healthcare disparities among racial and minority groups, also contributes, the agency says.

Half of men with syphilis are also infected with HIV, the CDC says.

The CDC recommends that gay and bisexual men get tested for HIV, syphilis, chlamydia and gonorrhea at least once a year. For men at high risk, the health agency recommends more frequent STD testing.

“We have a lot of providers that don’t realize that syphilis is back,” Bolan tells Reuters. “They think this is a disease of years past. It’s critical that they do a sexual history so that they can improve screening for these men.”

HIV is on the rise among gay men, too.

[graphic via CDC]