BOSTON (Reuters) - A drug-resistant "superbug" previously found almost exclusively in hospitals is becoming more common in the community and must be aggressively treated, two teams of experts reported on Wednesday. Staphylococcus aureus, or staph, infections that are resistant to methicillin and similar drugs can now be put into the category of flesh-eating bacteria, the experts report in the New England Journal of Medicine. Doctors need to be aware of this and switch to different antibiotics at the first sign of trouble. "The alarm does need to be raised to people and clinicians that if you have a staph infection and it's not getting better, you'd better go back to your doctor," said Scott Fridkin, a epidemiologist with the Centers for Disease Control and Prevention, who led one study. "The bad news is that staph causes a lot of skin infections and they've always been difficult to treat," he added. "Now we have a staph that's biologically different and resistant to first-line antibiotics." Staphylococcus aureus is usually harmless and very common, found on skin or in the noses of about 30 percent of people. It can cause stubborn problems such as boils and is often mistaken for a spider bite. Until now, most of the infections caused by methicillin-resistant Staphylococcus aureus or MRSA have shown up in hospitals. But up to 20 percent of such infections may have come from the community, Fridkin said in a telephone interview. "We were surprised to find it that high," he said. The group had expected the rate to be close to zero at the start of the study in 2001. "It wasn't there a decade ago, but it's there now." The second study, led by Loren Miller of Harbor-University of California Los Angeles Medical Center in California, found that some cases of flesh-eating bacteria are caused by methicillin-resistant staph. Over a 15-month period, they found 14 such instances, and four patients had no risk factors such as drug use, diabetes or hepatitis.