MRSA infections not limited to hospitals

In vulnerable people S. aureus (red) can cause wound infections pneumonia and blood poisoning.
In vulnerable people S. aureus (red) can cause wound infections pneumonia and blood poisoning.

At a glance

  • Incision and drainage are recommended as primary treatment for most cutaneous abscesses and boils.
  • Oral antibiotic options are rated as equivalent. The choice may depend on such factors as patient allergies and cost.
  • Decolonization is a second-line treatment to be considered when infection has recurred.
  • Invasive MRSA infection almost always requires hospitalization and treatment with IV antibiotics.
Infections caused by methicillin-resistant Staphylococcus aureus (MRSA)—strains of the organism that don't respond to first-line antibiotics—have long been a problem in health-care settings. Their prevalence has grown and moved beyond hospital walls in recent years, however, leading the Infectious Diseases Society of America to issue its first practice guidelines for the management of MRSA infections (Clin Infect Dis. 2011;52:e18-55).

"In the past 10 years, community-associated MRSA (CA-MRSA) has emerged and become a significant problem," says Catherine Liu, MD, of the University of California, San Francisco, and chair of the committee that wrote the practice guidelines.

Unlike the organism seen in health-care-associated MRSA (HA-MRSA) infection, CA-MRSA is typically susceptible to a variety of non-β-lactam antibiotics, "although clinicians may begin to see resistance emerge over time as they treat more infections," warns Dr. Liu.

Primary-care practitioners (PCPs) are most likely to encounter CA-MRSA in the context of minor skin and soft-tissue infections (SSTIs). "But it is also a significant cause of more invasive, serious disease" that requires hospitalization, Dr. Liu says. One recent study estimated that MRSA is responsible for 18,000 deaths per year.

While most skin abscesses caused by MRSA will resolve readily with drainage and appropriate antibiotic therapy, some are more severe or extensive and may progress to invasive disease, notes Dr. Liu. "It is hard to predict. I have seen bad outcomes in some patients who are otherwise healthy and without any risk factors."

The potential for such complications and recurrent disease underscore the importance of managing even minor infections carefully when MRSA may be involved, adds Dr. Liu.

Managing SSTIs

The guidelines recommend incision and drainage as primary treatment for most cutaneous abscesses and boils in the absence of complicating factors.

More severe infections or those involving multiple sites merit antibiotic therapy, as does disease that progresses in the context of cellulitis or indications of systemic illness. Consider antibiotics at the outset for patients with significant comorbidity or immune suppression, for the very young or old, or in sites that are difficult to drain. Drug treatment should be initiated promptly when the response to incision and drainage is inadequate.

Awareness of local epidemiology is useful, and PCPs should obtain cultures when possible. But given the prevalence of MRSA in the United States (responsible for up to 60% of SSTIs treated in the emergency department), "empirical therapy for CA-MRSA is recommended pending culture results," the authors write.

Oral antibiotics with activity against MRSA include clindamycin, trimethoprim-sulfamethoxazole, doxycycline, minocycline, and linezolid. "We rate these options as equivalent," affirms Dr. Liu. "They haven't been compared with one another." The choice may depend on such factors as patient allergies and cost, she says.

The treatment of cellulitis is more complex and may depend on the presence of purulent drainage or exudate. "The emergence of CA-MRSA has forced us to redefine how we think about cellulitis," comments Dr. Liu. The most common organisms involved in cellulitis are S. aureus and β-hemolytic streptococci, and the usual treatment, previously, was an antibiotic that would cover both, such as a β-lactam (cephalexin or dicloxacillin). But none of these agents is active against MRSA.

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