A once-rare drug-resistant germ now appears to cause more than half of all skin infections treated in U.S. emergency rooms, say researchers who documented the superbug's startling spread in the general population. Many victims mistakenly thought they just had spider bites that wouldn't heal, not drug-resistant staph bacteria. Only a decade ago, these germs were hardly ever seen outside of hospitals and nursing homes. Doctors also were caught off-guard — most of them unwittingly prescribed medicines that do not work against the bacteria. "It is time for physicians to realize just how prevalent this is," said Dr. Gregory Moran of Olive View-UCLA Medical Center, who led the study. Another author, Dr. Rachel Gorwitz of the Centers for Disease Control and Prevention, said: "I think no one was aware of the extent of the problem." Skin infections can be life-threatening if bacteria get into the bloodstream. Drug-resistant strains can also cause a vicious type of pneumonia and even "flesh-eating" wounds. The CDC paid for the study, published in Thursday's New England Journal of Medicine. Several authors have consulted for companies that make antibiotics. Researchers analyzed all skin infections among adults who went to hospital emergency rooms in 11 U.S. cities in August 2004. Of the 422 cases, 249, or 59 percent, were caused by methicillin-resistant Staphylococcus aureus, or MRSA. Such bacteria are impervious to the penicillin family of drugs long used for treatment. The proportion of infections due to MRSA ranged from 15 percent to as high as 74 percent in some hospitals. "This completely matches what our experience at Vanderbilt Children's Hospital has been," said Dr. Buddy Creech, an infectious-disease specialist whose hospital was not included in the study. "Usually what we see is a mom or dad brings their child in with what they describe as a spider bite that's not getting better or a pimple that's not getting better," and it turns out to be MRSA. The germ typically thrives in health-care settings where people have open wounds and tubes. But in recent years, outbreaks have occurred among prisoners, children and athletes, with the germ spreading through skin contact or shared items such as towels. Dozens of people in Ohio, Kentucky and Vermont recently got MRSA skin infections from tattoos. The good news: MRSA infections contracted outside a hospital are easier to treat. The study found that several antibiotics work against them, including some sulfa drugs that have been around for decades. A separate study in the journal reports the effectiveness of Cubicin, an antibiotic recently approved to treat bloodstream infections and heart inflammation caused by MRSA. However, doctors need to test skin infections to see what germ is causing them, and to treat each one as if it were MRSA until test results prove otherwise, researchers said. "We have made a fundamental shift in pediatrics in our area" and now assume that every such case is the drug-resistant type, Creech said. And, doctors need to lance the wound to get rid of bacteria rather than relying on a drug to do the job. "The most important treatment is actually draining the pus," Gorwitz said. Many times that is a cure all by itself, she said. The study was done in Albuquerque, N.M.; Atlanta; Charlotte, N.C.; Kansas City, Mo.; Los Angeles; Minneapolis; New Orleans; New York; Philadelphia; Phoenix; and Portland, Ore.