The Allegheny County Health Department has reported an unusually high number of syphilis cases in McKeesport, with 12 cases recorded in 2007 and 11 already documented for the first half of 2008.

Health department officials are stopping short of calling it an epidemic, instead saying it's a "cluster" since the disease is affecting a small area rather than the entire county.

"That's not a huge number, but it's somewhat more than you would expect from McKeesport, given its population," said Guillermo Cole, a spokesman for the health department.

If the current trend holds, however, McKeesport is on track to double its number of syphilis cases in 2008.

The health department compiles data on all syphilis cases in the county, but McKeesport, population 24,000, has a disproportionately high rate of the sexually transmitted disease in its early stage.

In 2007, there were 87 cases of early-infection syphilis in Allegheny County. Six months into 2008, there have been 41, which is not an alarming number, Mr. Cole noted.

The concentration of syphilis cases in McKeesport is confined to a small circle of people, he said, including prostitutes and their customers. Most of the cases were reported in men and women in their mid-30s who listed McKeesport mailing addresses.

"They know each other," Mr. Cole said. "It's in a fairly well-defined area of McKeesport.

"There's definitely a link to prostitution as well as drugs, sex for money and sex for drugs."

Syphilis is transmitted through direct contact with a syphilis sore, usually during sexual intercourse. The sores, called chancres, usually appear on the genitals or the lips and mouth. The disease is highly treatable and can be cured. If it goes untreated, however, long-term effects include heart disease, brain damage and, in rare cases, death.

Once a case of syphilis has been reported to the health department, officials ask the person to notify their recent sexual partners, or "contacts."

"The testing and treatment of contacts will slow and hopefully stop the spread of the infection" in the community, Mr. Cole said. But it can be difficult to track down all of the person's recent sexual partners, since they might have a transient lifestyle or not return phone calls.

The number of syphilis cases in Allegheny County has been falling since reaching a peak in 2006, when 105 cases were reported countywide. That year, 20 of them were in McKeesport.

But even if rates in the county and in McKeesport have fallen, the numbers for this year still look high enough to cause worry among health officials.

"If this holds up," Mr. Cole said, "we may see McKeesport accounting for as many as one-quarter of all the syphilis cases in the county [for 2008]."

Compared to gonorrhea and chlamydia, the incidence of syphilis is quite low, noted Mr. Cole. In Allegheny County last year, there were 2,163 gonorrhea cases and 4,897 cases of chlamydia.

The Allegheny County Health Department offers free and confidential testing and treatment for sexually transmitted diseases at its office at 3441 Forbes Ave., Oakland.