For the first time in three decades, the nation's most common sexually transmitted disease is a little less common.

Health officials on Tuesday said the rate and number of chlamydia (kluh-MID'-ee-uh) cases fell last year, by 1.5 percent. But there were still 1.4 million new cases reported - more than any other sexually transmitted disease. Experts are not sure what to make of the one-year drop.

Chlamydia is easily treated with antibiotics. Untreated, it can damage a woman's reproductive system.

The Centers for Disease Control and Prevention also reported gonorrhea cases declined, by less than 1 percent. The numbers for the most contagious forms of syphilis rose about 10 percent - to 17,375. The increase was mainly among gay men.