FRIDAY, Jan. 6 (HealthDay News) -- New research suggests that the gonorrhea-like condition known as urethritis, perhaps the most common sexually transmitted disease, can spread to men when they're on the receiving end of fellatio.

"This one really nails it down," said Dr. Hunter Handsfield, a professor of medicine at the University of Washington who wrote a commentary about the findings.

Urethritis, a condition related to a number of health problems, such as urinary tract infections and some sexually transmitted diseases, causes inflammation of the urethra. It can lead to genital discharge, burning during urination and redness and swelling at the tip of the penis, said Dr. Jeffrey D. Klausner, director of STD Prevention and Control Services with the San Francisco Department of Public Health. The symptoms "usually signify an infection due to a germ, like a bacteria or virus," he said.

Urethritis usually goes away on its own or is easily treated with antibiotics, Klausner said. But in some cases, it can result in serious complications, including permanent damage to the urethra in both men and women, especially if it's not treated.

According to Handsfield, urethritis brings more men to sexually transmitted disease clinics in the United States than any other condition or disease, and it may be the most common STD among both men and women.

In the new study, Australian researchers recruited 329 men with urethritis symptoms that weren't related to gonorrhea and 307 healthy men. The researchers tested the men and asked them about their sexual habits.

About five percent of the cases were directly related to germs from the mouth, including adenoviruses and a form of herpes. The researchers also found that urethritis without an apparent cause was more common in men who were on the receiving end of oral sex from their female or male partners.

The study findings appear in the Dec. 28 online edition of the Journal of Infectious Diseases.

The research points to the potential influence of normally innocuous germs in the mouth, Handsfield said. "It suggests that some of these cases might be due to bacteria that are entirely normal when they're in the mouth but cause inflammation in the urethra."