A new national record was set last year in cases of chlamydia -- more than 1 million cases -- according to figures released yesterday by the Centers for Disease Control and Prevention.

Increases in the national figures were also reported for cases of gonorrhea and syphilis in the CDC's Sexually Transmitted Disease Surveillance 2006 report.

In contrast, although syphilis cases were up, Allegheny County's cases of gonorrhea and chlamydia declined in 2006 .

Last year, the county had 4,195 cases of chlamydia, an incidence rate of 342.9 per 100,000 population. There were 4,302 reported cases in 2005. Nationally, the CDC said, there were 1,030,911 chlamydia diagnoses, an incidence rate of 347.8 cases and a 5.6 percent increase from 2005.

Through September 2007, county diagnoses for the most commonly reported infectious disease in the U.S. was 3,009, about the same rate as in 2006.

More aggressive screening has helped keep the numbers of chlamydia cases on an even keel, said Dr. Bruce Dixon, director of the Allegheny County Health Department. He pointed out that women have the highest rates of chlamydia.

The CDC said gonorrhea rates are jumping again after hitting a record low, and an increasing number of cases are caused by a "superbug" version resistant to common antibiotics.

Studies have shown a resistance to fluoroquinolones, a leading class of antibiotics that were used against gonorrhea, particularly among men who have sex with men. The CDC now recommends treatments using a single class of antibiotics called cephalosporins.

Syphilis diagnoses nationally totaled 9,756 last year, up from 8,724 in 2005. The rate of congenital syphilis -- which can deform or kill babies -- rose for the first time in 15 years.

"Hopefully we will not see this turn into a trend," said Dr. Khalil Ghanem, an infectious diseases specialist at Johns Hopkins University's School of Medicine.

In Allegheny County, 71 cases of primary and secondary syphilis -- the easily cured but most infectious stages of the disease -- were reported here last year, up over the 61 reported in 2005.

Although that county increase was 17 percent, Dr. Dixon said the number is too small to count as a trend.

"If you look at the start of this [21st] century, we were in single numbers," he said. "Now we'll probably end with 50 or so cases this year."

This year's lower rate may represent a more significant change, he said, adding that the county is now aggressive in its clinics, screening for and treating syphilis early.

"We're always concerned about syphilis," he said. For many people, he said it takes several doctor's visits before the rash that is the symptom of secondary syphilis is diagnosed correctly. Many doctors have never seen it before.

Dr. Dixon said the county has also been aggressive in keeping gonorrhea cases down.

In the county there were 1,620 cases of gonorrhea reported in 2006, compared to 1,804 in 2005, the highest number since the county began recording the cases in October 1991. The 2006 total means an incidence rate of 132.4 cases, which compares to a national rate of 120.9 and a countrywide total of 358,366.

Locally, a total 1,492 cases were reported through the first nine months of 2007.

"We haven't had the problems normally related to a city of our size," he said, adding that people are getting treatment for gonorrhea both in public clinics and private doctor's officies. "We've had an aggressive screening program in emergency rooms."

Though highly treatable, all three sexually transmitted diseases can have serious health complications if they go undetected and untreated. They range from pelvic inflammatory disease, ectopic pregnancy, infertility, and to increased susceptibility to HIV if exposed.