An antibiotic-resistant infection, which used to be primarily confined to hospitals, appears to be spreading in the community.

A new study at Children's Hospital of Philadelphia observed a significant rise in antibiotic-resistant Staphylococcus aureus - commonly called staph - infections in children who hadn't been recently hospitalized.

"It is a concern because it is a difficult-to-treat bacteria," said Louise Dembry, scientific program director for the Society of Healthcare Epidemiology of America meeting in Philadelphia this week, where the study was to be presented yesterday.

"If we are not careful now about preventing transmission of this, then we are going to have a potentially bigger problem," she said.

Antibiotic resistance has become a major public health problem as many bacteria have adapted to outfox the drugs designed to subdue them.

Barry Farr, a University of Virginia professor of medicine and epidemiology, said antibiotic-resistant staph - called methicillin-resistant Staphylococcus aureus (MRSA) - has occasionally shown up in communities for decades, but now is cropping up more frequently.

Meanwhile, the problem has soared in U.S. hospitals, he said. In 1980, 2 percent of all staph infections in hospitals were antibiotic-resistant. Now, in intensive-care units, half are, Farr said.

Staph bacteria are common and often live uneventfully on a person's skin. But if the skin is cut or scraped, the bacteria can invade and lead to a relatively common skin infection. Typically, the infection is treated with antibiotics in the penicillin family. If the bacteria becomes resistant to the antibiotics, experts say treatment choices dwindle.

In a paper presented yesterday, researchers at Providence St. Vincent Medical Center in Portland, Ore., identified an unusual cluster of 10 patients last summer treated in the hospital's emergency room for antibiotic-resistant staph infections. They not only had MRSA, but also were resistant to another kind of antibiotic treatment - clindamycin.

While some patients were considered at higher risk for community-acquired MRSA infection, more recently, said Nancy Church, the medical center's manager of infection control, "we're seeing these infections in patients who have no known risk factors."

Among 79 children identified at Children's Hospital of Philadelphia with MRSA from 2001 to 2003, about half had not been recently hospitalized, according to Susan Coffin, a study author and medical director of Children's Hospital's infection control department. Among 305 children treated for staph infections, the yearly percentage with resistant bacteria rose from 15 percent to 38 percent during that period, Coffin said.

She said it is unclear why the resistant bacteria have appeared in groups previously considered at low risk. (Besides hospital patients and health-care workers, other groups previously considered at higher risk were prisoners, men who have sex with men, and athletes in close contact sports.)

The antibiotic-resistant bacteria are transmitted through direct contact with other infected people or through contaminated objects such as combs, soap and sheets, experts said. Washing - hands, wounds and potentially contaminated objects - would help prevent the spread of the bacteria.

Data do not indicate that the resistant bacteria is any more dangerous than typical staph, but it can be more difficult to treat, Coffin said.

"Any serious-looking skin infection should be promptly seen by a doctor," Coffin said.

She advised people to look for warning signs, including blisters, boils or other skin wounds that are red or swollen; an unusually sensitive wound; or wounds accompanied by fevers.

"Most minor skin wounds will heal rapidly if they are washed with soap and water and kept clean," Coffin said. "If the wound doesn't get better, or appears to become worse despite these measures, there may be a staph infection."