Methicillin-resistant Staphylococcus aureus is now the most common identifiable cause of skin and soft-tissue infection seen in patients presenting to emergency departments in many U.S. cities.
Clinicians now should reconsider standard empirical antibiotic therapy in regions where methicillin-resistant Staphylococcus aureus (MRSA) is prevalent, and perhaps switch to drugs that provide MRSA coverage. And health care workers should take precautions such as using gowns and gloves when treating any patient with purulent skin or soft-tissue infection, according to Dr. Gregory J. Moran of the departments of emergency medicine and infectious diseases at Olive View-UCLA Medical Center, Sylmar, Calif., and his associates.
Since data concerning the prevalence of MRSA skin and soft-tissue infections have been scarce, Dr. Moran and his associates investigated the issue among 422 adults presenting to university-affiliated emergency departments in August 2004, in 11 cities in geographically diverse regions throughout the country. The median patient age was 39 years (range 18–79 years), and 62% of the subjects were men. Approximately half of the group was black, one-fourth was white, 22% were Hispanic, and the rest belonged to other racial groups.
The infections involved the upper extremities (29%), lower extremities (27%), torso (17%), perineum (14%), or head and neck (13%). They were classified as abscesses in 81% of patients, infected wounds in 11%, and cellulitis with purulent exudates in 8%. S. aureus was isolated in 320 patients, and 249 (78%) of these were MRSA isolates. “MRSA was the most common identifiable cause of skin and soft-tissue infections in 10 of the 11 emergency departments,” and the prevalence ranged from 15% to 74%, the researchers said (N. Engl. J. Med. 2006;355:666–74).
MRSA was isolated from 61% of abscesses, 53% of purulent wounds, and 47% of cellulitis cases, and 99% of the strains were community acquired rather than health care related. This is consistent with reports of dramatic rises in community-associated MRSA (CA-MRSA) in the past few years, the investigators said.
“Although more than 80% of patients with skin and soft-tissue infections associated with MRSA in this study received empirical antimicrobial therapy for their infections, the infecting isolate was resistant to the agent prescribed for 57% of these patients. This finding suggests a need to reconsider empirical antimicrobial choices for skin and soft-tissue infections in areas where MRSA is prevalent in the community,” they noted.
Of the MRSA isolates tested for drug susceptibility, 100% were susceptible to trimethoprim-sulfamethoxazole and rifampin, 95% were susceptible to clindamycin, 92% to tetracycline, 60% to fluoroquinolones, and 6% to erythromycin.
Even though most patients with MRSA abscesses were treated with β-lactam agents such as cephalexin and dicloxacillin, which are ineffective against MRSA isolates, there were no significant differences in outcomes between them and the patients whose isolates were susceptible to the drug they received.
The patients who received inappropriate antibiotics probably were cured by the drainage of the abscess and other wound care they received along with the drugs, suggesting that “most simple skin abscesses, even when caused by MRSA, can be cured with adequate drainage alone,” Dr. Moran and his associates said.
“The susceptibility of a given pathogen to prescribed antimicrobial agents may be more likely to affect the outcome among patients with cellulitis or purulent wounds. Unfortunately, there were insufficient numbers of these patients with follow-up information in our study to assess this relationship,” they added.
Patients with MRSA infection were more likely than were those with other bacterial infections to report that they believed their lesions resulted from spider bites, perhaps because these MRSA strains cause unusually painful lesions.