CA-MRSA: A new bug with a familiar name

Culturing staph infections is necessary in many parts of the country to prescribe the correct antibiotic.

By Susan J. Landers — Posted Nov. 22, 2004

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Washington -- A new strain of methicillin-resistant Staphylococcus aureus has settled into some communities, and physicians everywhere are being warned to keep an eye out for it.

While infection with MRSA is well-known in hospitals, the new strain of resistant bacteria is found among people without traditional risk factors.

Dubbed community-associated MRSA, or CA-MRSA, by the Centers for Disease Control and Prevention, the bacteria differ genetically from the more familiar hospital-acquired MRSA, said researchers at the Interscience Conference on Antimicrobial Agents and Chemotherapy held Oct. 30 to Nov. 2 in Washington, D.C.

CA-MRSA is infecting seemingly healthy people, often children, and causing primarily skin and soft-tissue lesions such as boils, abscesses and cellulitis, which are frequently misdiagnosed as spider bites.

The bacteria already have taken up what is likely to be permanent residence in parts of California, Texas and Georgia. Several outbreaks have occurred in prisons, in military bases and among members of athletic teams throughout the country.

Physicians in communities in which the strain is now endemic recommend a cautious treatment approach, particularly when prescribing an antibiotic.

There is often an incorrect assumption that the skin or soft-tissue infection being treated is caused by a susceptible strain of staph, said Elizabeth Bancroft, MD, a medical epidemiologist at the Los Angeles County Dept. of Health Services who has studied outbreaks in her county. All too often, the antibiotic prescribed does nothing to slow the infection.

Physicians should "regard all lesions with suspicion, especially if you live in areas where CA-MRSA is prevalent," she advised.

"Once it's in the community, you've got to think about it," said Sheldon Kaplan, MD, professor of pediatrics at Baylor College of Medicine in Houston and chief of the infectious diseases service at Texas Children's Hospitals. "In our area, it's just the regular staph now."

"Physicians should be aware of what's going on in their community," he said. "If you aren't seeing a lot of these MRSA infections, then there is not anything special you need to do."

Overcoming resistance

Still, when it comes to prescribing the correct antibiotic, no assumptions can be made.

"In the past, when people saw it was an abscess, they would just assume it was a staph germ and treat it with common antibiotics," Dr. Kaplan said. But those common antibiotics aren't likely to work on this bug.

In addition, there are regional differences, according to an article in the September issue of AAP News, published by the American Academy of Pediatrics. For example, clindamycin-resistant MRSA strains are common in Chicago but infrequent in Houston.

Incision and drainage should be considered the No. 1 treatment for boils and abscesses, Dr. Bancroft said, and cultures should be obtained to help determine which antibiotic to prescribe and avoid prescribing an antibiotic to which the bacteria have become resistant, which now include the beta-lactamase inhibitors.

If a patient improves after an incision and drainage, an antibiotic may not even be necessary, she said. Careful consideration before prescribing an antibiotic also helps limit the development of additional resistant strains of bacteria. "You want to keep the bug as sensitive as possible."

In addition to skin infections, Robert Daum, MD, of the University of Chicago's Children's Hospital, said he and his colleagues were seeing a pyramid of disease caused by CA-MRSA. The majority of cases involve skin infections, but a few cases of severe sepsis are clustered at the pyramid's peak. Dr. Daum spoke at the ICAAC meeting.

Preventive measures also make sense, said John Jernigan, MD, an epidemiologist at the CDC, who also spoke at the ICAAC meeting.

Because there are common themes to the spread of the infections -- including crowding, frequent skin-to- skin contact, compromised skin integrity and contaminated surfaces -- there are some simple precautions that can be taken to check the spread, he said. Careful cleaning of shared equipment and proper care of wounds, including covering them, and good personal hygiene are among those measures.

"There is a role for being a little more careful in the outpatient setting regarding cleaning surfaces," Dr. Jernigan said. In addition, patients should be told to practice good household hygiene -- for example, don't share towels.

An outbreak of MRSA skin infections among players on a college football team in Connecticut was stemmed in part by properly disinfecting the whirlpools and installing antibacterial soap dispensers in the athletes' showers, according to a study published in the Nov. 15 issue of Clinical Infectious Diseases.

The study found that cornerbacks and wide receivers who frequently come in direct contact with other players accounted for the most cases. More cases were also detected among players who had sustained "turf burns" and among those who had shaved their bodies, thus causing small breaks in the skin through which the bacteria gained access.

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Stemming staph

The American Academy of Pediatrics has developed new principles for physicians to use in managing skin and soft-tissue infections. They include:

  • Seeking information about the prevalence of community-associated methicillin-resistant Staphylococcus aureus in their areas.
  • Culturing purulent skin or soft-tissue lesions before further management.
  • Adequately draining abscesses at presentation and sending material for culture and susceptibility testing.
  • Determining the severity of infection at presentation.
  • Providing discharge instructions emphasizing the need for return if no clinical improvement occurs within 48 hours.

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External links

AMA Council on Scientific Affairs report on antibiotic resistance (no longer available)

Fact sheet on community-associated methicillin-resistant Staphylococcus aureus skin infections from the Los Angeles County Dept. of Health Services (link)

Fact sheet on methicillin-resistant Staphylococcus aureus from the Centers for Disease Control and Prevention (link)

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