TUESDAY, Nov. 24 (HealthDay News) -- Strains of antibiotic-resistant infections normally found in the community are increasingly showing up among hospital outpatients, raising the risk that inpatients could become infected, new research says.

From 1999 to 2006, researchers found a sevenfold increase in the incidence of outpatients with methicillin-resistant Staphylococcus aureus (MRSA) infections. Outpatients include people treated in emergency departments or surgical centers but not admitted, or at doctors' offices associated with hospitals.

This poses a risk to inpatients because many resources are used by both sets of patients. These include surgical centers and the doctors themselves, who often treat patients both inside and outside of hospitals.

"What this is suggesting is that outpatients are a significant source of MRSA, especially community-associated MRSA strains," said the study's lead author, Eili Klein, a doctoral candidate at Princeton University and a researcher at Resources for the Future, a Washington, D.C.-based think tank. "This suggests the need for incentives to make sure hospitals are not only taking steps to prevent hospital-associated strains from spreading among inpatients, but preventing the spread of community-associated strains through shared resources."

The study is published in the December issue of Emerging Infectious Diseases.

MRSA, which burst into the public consciousness in the 1990s, is named for its resistance to methicillin and other antibiotics. There are several strains, including those that emerged in hospitals, called "hospital associated," and those that emerged outside hospitals and tend to spread in schools and gyms, called "community associated."

While both types can cause serious, life-threatening illness, hospital-acquired strains are generally more virulent. The bacteria can get into wounds, causing deadly blood or lung infections. About 20,000 people in the United States die each year from the MRSA infections, according to background information in the study.

Community-associated strains have also caused some deaths in otherwise healthy people, including several children who were killed by MRSA infections in the late 1990s. Typically, however, community-associated strains cause skin or other soft tissue infections that are treatable with newer antibiotics.

According to the research, the number of hospital-associated infections remained relatively stable from 1999 to 2003, even decreasing a bit from 2003 to 2005. Some of the reduction was due to better infection-control measures, such as more thorough and frequent hand washing among doctors, Klein said.

Community-associated strains, however, are becoming far more commonplace. Among outpatients with staph infections, MRSA infections increased by more than 90 percent, according to the data culled from 300 microbiology labs serving hospitals across the nation.

Most of the increase was due to community-associated strains, which rose from 3.6 percent of all MRSA infections in 1999 to 28.2 percent in 2006, the study found.

The increases pose a risk to hospital inpatients, who may become infected by contaminated equipment in surgical centers used for inpatients and outpatients or by the doctors themselves.

The study did not find an increase in hospital-associated strains spreading in the community.

After hearing reports of community-associated MRSA strains showing up in hospitals, the U.S. Centers for Disease Control and Prevention analyzed the data it has collected on invasive MRSA infections, said Dr. Fernanda Lessa, a CDC medical epidemiologist.

The CDC report found that the proportion of community-associated MRSA infections in hospitals, compared with MRSA infections overall, remained small and that the infections were no more virulent than those already present.

"So far it hasn't been a big problem," Lessa said. "Our data suggested the community-associated strain doesn't seem to be taking off in hospitals and is not causing worse disease."

Other research also has shown a rise in community-associated strains. A study in the January issue of Archives of Otolaryngology Head & Neck Surgery found that MRSA infections in the ears, nose or sinuses of children more than doubled from 2001 to 2006, going from 12 percent to 28 percent of head-and-neck area infections.

More information

The U.S. Centers for Disease Control and Prevention has more on MRSA.

SOURCES: Eili Klein, doctoral candidate, Princeton University, Princeton, N.J., and researcher, Resources for the Future, Washington, D.C.; Fernanda Lessa, M.D., M.P.H., medical epidemiologist, division of healthcare quality promotion, U.S. Centers for Disease Control and Prevention, Atlanta; December 2009, Emerging Infectious Diseases

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