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MRSA: Moving into the Community

Methicillin-resistant Staphylococcus aureus (MRSA) has been endemic in hospitals worldwide for 40 years. Infection is most commonly healthcare-associated, occurring in patients who have had recent hospitalization, surgery, dialysis, indwelling catheters, or residence in long-term–care facilities. Recent outbreaks of MRSA infections in prisons were notable because some hosts had none of the established risk factors (JWEM Jan 6 2004). Several recent reports highlight the growing problem of community-acquired MRSA.

CDC researchers conducted a surveillance study of all cases of MRSA infection in Atlanta, Baltimore, and several regions of Minnesota from 2001 through 2002. Infections were categorized as community-acquired if patients had none of the established risk factors. Of all MRSA isolates collected, 8% to 20% were community-associated. Such infections were significantly more common among individuals younger than 2 years than among older individuals (relative risk, 1.51) and among blacks than among whites in Atlanta (age-adjusted RR, 2.74). Seventy-seven percent of cases involved skin infections, and 6% of cases were invasive infections, including bacteremia and pneumonia. In 73% of cases, patients were initially prescribed antimicrobials to which the organism was resistant, but, strikingly, the lack of sensitivity did not appear to affect outcomes. Overall, 23% of patients were hospitalized for their MRSA disease.

In another study, investigators focused on necrotizing fasciitis and myositis, deep soft-tissue infections that are usually caused by group A streptococcus and often are polymicrobial. Using records from a 15-month period at a Los Angeles hospital, the authors retrospectively identified 843 patients whose wound cultures grew MRSA. Of these patients, 14 had surgically confirmed necrotizing fasciitis or myositis caused by community-acquired MRSA. In 86% of these cases, wound cultures were monomicrobial for MRSA. The median hospital stay was 10 days, and extensive surgery was common. Most patients had conditions or risk factors that would predispose them to MRSA infection, such as hospitalization in the past year, homelessness, and injection drug use. The authors note that current treatment recommendations for necrotizing fasciitis and myositis do not include antibiotics that are active against MRSA.

Finally, researchers in Washington, DC, report on four cases of deep soft-tissue infection caused by MRSA that occurred during a 6-month period. Two patients had no history of medical problems. All isolates were resistant to azithromycin but sensitive to clindamycin. Two isolates were tested against ciprofloxacin and were resistant. All patients were treated with vancomycin, and all had complete resolution of their infections.

An editorialist recommends increased vigilance for MRSA, a lower threshold for obtaining cultures, and use of antibiotics (e.g., vancomycin) that are active against MRSA to treat hospitalized patients who have suspected staphylococcal infection, even if they have none of the usual risk factors for MRSA. The proper outpatient treatment is less clear, as it is not known whether antibiotics that are active against MRSA have any effect on the outcome of soft-tissue infections.

Comment: Emergency physicians are often criticized for overtesting, but these findings demonstrate that skin and soft-tissue infections are getting more complicated, thereby adding to the difficulty of clinical decision making. In the past, skin abscesses often needed just to be incised and drained, and cultures were not necessary because antimicrobials were not indicated. Now, however, it appears that cultures are indicated if for no other reason than surveillance. The important — and as yet unanswered — question is what to do when a wound isolate from a discharged patient is subsequently reported as growing MRSA.

— J. Stephen Bohan, MD, FACP, FACEP

Published in Journal Watch Emergency Medicine May 11, 2005

Citation(s):

Fridkin SK et al. Methicillin-resistant Staphylococcus aureus disease in three communities. N Engl J Med 2005 Apr 7; 352:1436-44.

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Miller LG et al. Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles. N Engl J Med 2005 Apr 7; 352:1445-53.

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Chambers HF. Community-associated MRSA — Resistance and virulence converge. N Engl J Med 2005 Apr 7; 352:1485-7.

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Ruiz ME et al. Pyomyositis caused by methicillin-resistant Staphylococcus aureus. N Engl J Med 2005 Apr 7; 352:1488-9.

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