Syphilis, on the verge of being eliminated in the United States about 10 years ago, also has been increasing. About 13,500 cases of the most contagious form of the disease were reported in 2008, up from about 11,500 the year before.
Unlike with chlamydia, health officials think syphilis cases are increasing. Syphilis rates are up among both gay men and heterosexuals, Douglas said.
Syphilis can kill if untreated, but chlamydia is not life-threatening. Neither is gonorrhea, which seams to have plateaued in recent years. Gonorrhea cases dropped to about 337,000 cases in 2008, down from about 356,000 in 2007.
Females ages 15 through 19 had the largest reported number of chlamydia and gonorrhea cases, accounting for more than one in four of those cases. But females are often screened more than other people, since 1993 federal recommendations that emphasize testing for sexually active women 25 and younger.
The government estimates there are roughly 19 million new cases of sexually transmitted disease annually.
Specialists say the most common is HPV, human papillomavirus, which can cause genital warts, cervical cancer, and other cancers.
