The troubling trend reverses a 14-year decline and shows the infection, already on the uptick among gay and bisexual men, is worsening in the heterosexual community, the team at the U.S. Centers for Disease Control and Prevention said.

If a woman is infected with syphilis while pregnant, her baby can be born dead, deaf, with other nerve damage or bone deformities. Antibiotic treatment at least a month before birth can prevent that.

CDC researchers checked cases of congenital syphilis, a reportable disease, which means doctors must report it to state health departments.

After declining for 14 years, the congenital syphilis rate among infants aged under 1 year increased 23 percent, from 8.2 cases per 100,000 live births in 2005 to 10.1 during 2008, the CDC team reported in the agency's weekly report on death and disease.

That increase followed a 38 percent increase in the ... syphilis rate among females aged more than 10 years from 2004 to 2007. The biggest increases were in the South and among black women.

Recent increases in ... syphilis among black women in the south have been linked to crack cocaine use and commercial sex work, the report added. Increases might portend a larger increase in the congenital syphilis rate in 2009 and future years.

Syphilis is a sexually transmitted disease caused by the Treponema pallidum bacteria. It often does not cause symptoms for years and can therefore be transmitted by people who are unaware they are infected.

Primary syphilis is usually heralded by a single sore called a chancre, and if not treated, patients can develop a rash, fever, swollen lymph nodes and other symptoms. Late-stage syphilis damages the brain, nerves, eyes, heart and other organs.

Last November, CDC officials said squeamishness about talking about sex had helped keep sexually transmitted infections common in the United States, which has among the highest rates of STDs of any developed country.

The CDC says 13,500 syphilis cases were reported in 2008, an almost 18 percent increase from 2007, with 63 percent of them among men who had sex with men.

(Editing by Peter Cooney)

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