Cases of antibiotic-resistant staph infections usually acquired in the community are growing in the United States and rapidly spreading to hospitals, researchers said.
Methicillin-resistant Staphylococcus aureus (MRSA), which can penetrate wounds and cause lethal bloodstream and lung infections, kills about 20,000 each year in the United States, according to the Centers for Disease Control and Prevention (CDC).
That is more deaths than the over 14,000 people who died from AIDS in the US in 2007.
Although the superbug has usually spread in hospitals, "the findings from this study suggest that there is a significant reservoir in the community as well," said lead author Eili Klein, researcher at Resources for the Future.
The study analyzed data from over 300 microbiology labs serving hospitals across the country, finding a seven-fold jump in the proportion of community-associated strains of MRSA at outpatient hospital units between 1999 and 2006.
This increase threatens the safety of patients because health care professionals and patients travel frequently between a hospital's inpatient and outpatient units, the authors warned.
More than 63,000 people die in the United States each year from hospital-acquired infections resistant to at least one antibiotic.
Although they are less virulent and susceptible to more antibiotics, community-associated strains can still cause significant illness and death, according to the study published in the December issue of "Emerging Infectious Diseases."
Those strains can be acquired in virtually any public place.
Researchers found that MRSA infections jumped by over 90 percent among outpatients with staph infections. The CDC say they now account for more than 60 percent of all staph infections.
The community-associated strains were responsible for most of the increase, rising from 3.6 percent of all MRSA infections in 1999 to 28.2 percent in 2006, according to the study.
MRSA strains accounted for 63 percent of all staph infections in 2004, up from 22 percent in 1995 and two percent in 1974, the CDC says.
In order to contain the risk of MRSA infection, Klein urged hospitals to reinforce infection control and surveillance measures.
"The movement of community-associated strains into the hospital also points to the urgent need for rapid tests that can identify the strain of MRSA," he said.
The authors noted that some MRSA strains, especially those originating from outpatient departments, are vulnerable to more cheap antibiotics, allowing a hospital doctor to prescribe an effective drug while keeping costs under control.
About 20 percent of those infected die from MRSA strains, according to the CDC. In the European Union, more than three million people are infected each year and tens of thousands die from the infections.