A rare sexually transmitted disease that can scar the genitals has been found in two patients in New York, and the strain is the same as that recently detected in Europe, the city’s health commissioner said Wednesday.

Lymphogranuloma venereum, or LGV, is a form of chlamydia that can damage the bowels and scar the anus. Among the few patients that have been identified in the United States, most also had the AIDS virus, Health Department Commissioner Thomas Frieden said at a news conference.

“We know LGV increases the risk of the spread of HIV because it causes ulcers and bleeding,” he said.

Frieden said the federal Centers for Disease Control and Prevention earlier confirmed three LGV cases in San Francisco and one in Atlanta. He said gay and bisexual men were urged to abstain from sex or limit their number of sex partners and use condoms.

Unprotected anal intercourse is the key risk factor for the spread of LGV. Symptoms include painful rectal infections, but the first symptom may be a painless pimple or lesion on the genitals.

If identified early, LGV can be treated with antibiotics. Untreated, it can cause permanent damage to the bowels and swelling and scarring of the genitals. Death is rare.

Dr. Susan Blank, New York’s assistant commissioner for sexually transmitted disease control, said the health department was treating the two cases as an “outbreak” in an aggressive effort to prevent the spread of what she called “a bad disease.”

An alert has been sent to physicians in New York.

In the past two decades LGV has primarily been found in the tropics. But in November, the Netherlands said 92 cases of LGV among gay and bisexual men had been reported there over the preceding year, compared to the usual two or three cases a year.

Frieden said cases also have been found in the United Kingdom.