ATLANTA — Cases of some common sexually spread diseases continue to increase in the United States, but the syphilis rate dropped last year for the first time in a decade.

Health officials on Thursday released their annual report on sexually transmitted disease, and found chlamydia and gonorrhea rates continued to grow last year.

More than 1.3 million cases of chlamydia were reported last year — the largest number ever reported in one year for any condition. The number of new gonorrhea cases surpassed 300,000.

Fewer than 14,000 Americans were reported last year to have the most contagious forms of syphilis. While the number affected is fairly small, the rate of new cases had been increasing since 2001, but dropped by about 2 percent in 2010.