One single strain of bacteria is causing most cases of drug-resistant Staphylococcus aureus found outside hospitals in the United States, U.S. researchers reported on Tuesday.
The USA300 strain of methicillin-resistant Staphylococcus aureus or MRSA is extraordinarily contagious and robust, the U.S. government researchers said.
"Our study confirms that a single strain, called USA300, of community-associated MRSA is responsible for many of the devastating infections which have spread rapidly across the United States in recent years," said Dr. James Musser of The Methodist Hospital Research Institute in Houston.
Staphylococcus, or staph for short, is a very common bacteria that causes pimples, boils and, occasionally, life-threatening infections.
Drug-resistant forms have become more common and in October, a report in the Journal of the American Medical Association showed that MRSA killed an estimated 19,000 Americans in 2005.
It found that 85 percent of them were infected in hospitals but a form found in schools, gyms and other public places is becoming more common too.
In one study, published in the Proceedings of the National Academy of Sciences, researchers found the samples of the USA300 strain of MRSA were all nearly identical genetically.
"The USA300 group of strains appears to have extraordinary transmissibility and fitness," said Dr. Frank DeLeo of the National Institute of Allergy and Infectious Diseases Rocky Mountain Laboratories in Hamilton, Montana.
"We anticipate that new USA300 derivatives will emerge within the next several years and that these strains will have a wide range of disease-causing potential."
In a second report, published in the Annals of Emergency Medicine, researchers found community-acquired MRSA was becoming more common but was not especially dangerous, despite its drug-resistant abilities.
"Our research shows that CA-MRSA has emerged as the most common cause of abscesses among otherwise healthy patients coming to the emergency department across the country," said Dr. Daniel Pallin of Brigham and Women's Hospital and Children's Hospital in Boston.
"While the increasing numbers of infections suggest that we are seeing an epidemic, it is an epidemic of mild illness for the most part, and reports of deadly complications are the exception more than the rule," Pallin added in a statement.
Pallin said his team found that that visits to U.S. emergency departments for skin infections almost tripled, from 1.2 million in 1993, to 3.4 million in 2005. But they noted that MRSA was easily treated.
"Community-associated MRSA is not a deadly super bug," said Dr. David Talan of the University of California Los Angeles, who wrote a commentary on the findings. "It is more like an aggressive honeybee: more apt to sting, but only rarely fatal."