WEDNESDAY, March 12 (HealthDay News) -- For the seventh year in a row, rates of syphilis infection have increased in the United States, driven largely by cases among gay and bisexual men, according to a new federal report.

"CDC's preliminary 2007 data indicate that the rate of primary and secondary syphilis -- the earliest and most infectious stages of the disease -- increased by 12 percent between 2006 and 2007," Dr. Hillard Weinstock, of the U.S. Centers for Disease Control and Prevention's Division of STD Prevention, said during a Wednesday teleconference. Weinstock spoke at the CDC-sponsored 2008 National STD Prevention Conference in Chicago.

The number of reported cases of syphilis increased from 9,756 in 2006 to 11,181 in 2007, Weinstock said. "This is the seventh consecutive annual increase in national syphilis rates," he said.

Continuing with recent trends, 2007 statistics showed that men who have sex with men accounted for the majority of syphilis cases in the United States and contributed significantly to the overall increase in the disease among men, Weinstock said.

"The syphilis rate among men increased 14 percent from 2006. It was six times higher than the rate among women. Men who have sex with men comprised approximately 64 percent of reported syphilis cases in 2007," he said.

The increase in the syphilis rates among gay and bisexual men is a significant health concern, Weinstock said. "Syphilis, like other STDs [sexually transmitted diseases], can increase the likelihood of HIV transmission two- to five-fold. For individuals already infected with HIV, syphilis can increase viral load, which can accelerate HIV disease progression and the potential for HIV transmission," he said.

The CDC recommends that gay and bisexual men be tested for syphilis and other STDs at least once a year. However, several other studies presented at the meeting found that the rates of STD screening among gay and bisexual men remain low.

"A combination of strategies is needed to reduce the burden of STDs among men who have sex with men," Dr. John Douglas, director of CDC's Division of STD Prevention, said during the teleconference. "Recognizing that there is no simple solution to the complex factors driving risk and transmission among men who have sex with men, CDC is taking a variety of steps," he added.

The agency is working with doctors and other public health officials to promote recommendations for STD and HIV testing. The CDC is also looking to increase STD testing in places other than doctors' offices, such as bathhouses and other settings where gay and bisexual men meet, Douglas said.

Although the majority of new cases of syphilis are among gay and bisexual men, syphilis is also increasing among women and African-Americans, officials said.

"The syphilis rate among women increased between 2006 and 2007 for the third consecutive year after a decade of decline," Douglas said. "The rate of syphilis among women increased 10 percent from 2006."

And, syphilis rates increased last year among African-Americans for the fourth consecutive year after more than a decade of decline. The rate of syphilis among African-Americans increased 22 percent from 2006 to 2007, Weinstock said.

Although the rate of syphilis infections among whites and African-Americans is narrowing, there is still a disparity. "In 2007, the syphilis rate among African-Americans was seven times higher than among whites. This represents a substantial decline from 1999 when the syphilis rate among African-Americans was 29 times that of whites," Weinstock said.

This decline represents a drop in cases among African-Americans and an increase in infections among white gay and bisexual men, Weinstock noted.

Syphilis is caused by the bacterium Treponema pallidum. An estimated 36,000 cases of the disease were reported in the United States in 2006. The germ is passed from person to person through direct contact with a syphilis sore, with sores mainly occurring on the external genitals, vagina, anus, or in the rectum, according to the CDC.

Early stages of infection are easily cured with the antibiotic penicillin. Late stages of the disease can develop in about 15 percent of people who have not been treated. Untreated syphilis can eventually damage internal organs, including the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. The damage can be serious enough to cause death, according to the CDC.

More information

For more on STDs, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: March 12, 2008, teleconference with Hillard Weinstock, M.D., and John Douglas, director, both with the Division of STD Prevention, U.S. Centers for Disease Control and Prevention, Atlanta

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