The increase extended a steady rise in sexually transmitted syphilis infection since 2000, when rates reached a 50-year low. Two-thirds of the new infections are now in men who have sex with men, what public health officials refer to as "MSMs," and are focused primarily among blacks in U.S. cities.
Nearly 8,000 syphilis cases were reported to federal officials in 2003. Though overall infection numbers remain relatively low, infection rates among those men were up more than 80% between 2000 and 2004.
"There are clear signs that syphilis increases have occurred among MSM," John Douglas, MD, director of CDC's division of sexually transmitted disease prevention, told reporters.
Officials also reported a 6% rise in cases of chlamydia in 2003. CDC recorded more than 900,000 cases, though officials estimated that as many as 2.8 million new infections occur each year.
Valdiserri says improved testing and diagnosis were the primary drivers behind the increase in reported chlamydia cases and that researchers have little evidence of overall increases in the disease's spread.
Still, chlamydia exacts a heavy toll on teenaged girls between 15 and 19 years old and women between 20 and 24 years old, who are the most likely groups to contract the bacteria through unprotected sex. Chlamydia usually causes no symptoms in women but can lead to pelvic inflammatory disease and complications of ectopic pregnancy and infertility if left untreated.
The CDC has recommended annual chlamydia testing for all sexually active women younger than 26 years of age, but few young women receive the tests, according to Douglas.
"Most cases of the disease remain undiagnosed and untreated," he says.
Higher Rates Among Minority Groups
Officials pointed to increasing racial disparities in syphilis, chlamydia, and gonorrhea rates. All of the diseases are now substantially more likely to infect blacks and other minority groups than they are whites, according to CDC figures. Black women were nearly eight times more likely than white women to contract chlamydia in 2003, Tuesday's CDC report noted.
At the same time, syphilis rates rose 17% in blacks between 2003 and 2004.
Rising syphilis cases among men who have sex with men are of particular concern to public health officials because they could indicate a resurgence in sex behaviors that increase transmission of HIV, the virus that causes AIDS.
Several studies now show that syphilis outbreaks in primarily Western U.S. cities coincide with increased use of methamphetamine a highly addictive stimulant drug. The drug causes an overwhelming high and often is present during casual sexual encounters where condoms are not used.
A recent British study suggested that natural peaks and valleys in human immunity cause decade-to-decade rises in syphilis infection rates. But Douglas called the evidence "far from compelling" and said that drug use and increasingly risky sexual behavior among men were mostly to blame.
"We do have some good evidence that men are engaging in higher-risk behaviors," Valdiserri says.
Tuesday's report also showed a 1.5% drop in infection rates of gonorrhea, a bacterial STD that peaked in the 1970s. The CDC recorded 330,000 infection reports in 2004, about half the estimated actual number of infections.