TUESDAY, Jan. 13 (HealthDay News) -- The number of Americans newly infected with the sexually transmitted diseases chlamydia and syphilis continues to rise, federal health officials reported Tuesday, with chlamydia infections hitting a record million-plus new cases annually.

The numbers, from 2007, show that cases of chlamydia as well as syphilis rose for the third year in a row, according to a report by the U.S. Centers for Disease Control and Prevention (CDC).

"The bad news from last year has continued," said Dr. John M. Douglas Jr., director of the CDC's Division of STD Prevention. "These infections remain at very high levels, and frankly, unacceptably high."

Chlamydia and gonorrhea, the two most commonly reported infectious diseases in the United States, together accounted for almost 1.5 million reported cases of sexually transmitted disease (STD) in 2007.

"Chlamydia is at a new all-time record 1.1 million cases -- it went up about 7 percent since 2006," Douglas said. "Gonorrhea is about at 355,000 cases."

STDs, although easily diagnosed and treated, frequently occur without symptoms and may go untreated. Left untreated, chlamydia and gonorrhea can result in pelvic inflammatory disease -- a condition that causes as many as 50,000 U.S. women to become infertile each year, according to the report, Sexually Transmitted Disease Surveillance, 2007.

The overall rate of chlamydia infections among women was 543.6 cases per 100,000 females, almost three times the rate among men -- 190 cases per 100,000 males, the report said.

The increasing number of chlamydia cases is actually a reflection of more people being screened, not a greater incidence of the disease in the population, Douglas said. "It's kind of a mixed piece of good news. We wish those numbers were going down, but we know they have to go up before they go down," he said.

Gonorrhea rates have been stable for about the last 10 years, Douglas said. "This is stable at quite a high level. It represents an example where we have a job half done. Gonorrhea has come down since its highpoint in the 1970s, but we just got stuck in the late 1990s, and we've been stuck ever since then," he said.