Sexually transmitted diseases continue to rise according to the latest study by the U.S. Centers for Disease Control and Prevention.

In 2008 there were 1.2 million new cases of chlamydia, a sometimes symptom-less infection that can lead to infertility in women. It was the most ever reported, up from the old record of 1.1 million cases in 2007. 

Better screening is the most likely reason, said Dr. John M. Douglas Jr. of the U.S. Centers for Disease Control and Prevention.

Syphilis, which was on the verge of being eliminated in the United States about 10 years ago, also has been on the rise. Statistics show that about 13,500 cases of the most contagious form of the disease were reported in 2008, up from about 11,500 the year before.

Syphilis can kill if untreated, but chlamydia is not life-threatening. Neither is gonorrhea, which appears to have plat eaued in recent years. Gonorrhea cases dropped to about 337,000 cases in 2008, down from about 356,000 cases.

Girls, 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 they're often screened more than other people, since 1993 federal recommendations that emphasize testing for sexually active women age 25 and under.

Syphilis, chlamydia and gonorrhea can all be treated with antibiotics but untreated can cause pelvic inflammatory disease, infertility, ectopic pregnancy and can infect newborns.

Overall, CDC estimates that 19 million new sexually transmitted infections occur each year, almost half among 15- to 24-year-olds.