MRSA in the Community
By Matthew T. Harbison, MD
Moran GJ, Krishnadasan A, Gorwitz RJ, et al. EMERGEncy ID Net Study Group. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. 2006 Aug 17;355(7):666-674.
Methicillin-resistant Staphylococcus aureus (MRSA) emerged as an issue in the healthcare community not long after the introduction of methicillin in 1959. MRSA has traditionally been thought of as an issue for those individuals who have contact with the healthcare system; however, there is growing evidence that MRSA has become an entity in the greater community at large, affecting individuals who have not spent significant time in healthcare facilities. Descriptions of several community-based outbreaks have led to the understanding that community-associated MRSA has different characteristics than MRSA infections contracted in the hospital setting. The community-associated isolates are resistant to fewer antibiotics, produce different toxins, and have differing genetic complexes responsible for antibiotic resistance. The majority of the community-acquired infections are skin and soft tissue infections, although more serious infections have been reported.
Moran and colleagues conducted a prospective prevalence study in adult patients presenting to emergency departments with skin and soft tissue infections in 11 metropolitan areas in geographically diverse regions of the United States. Eligible patients 18 and older with purulent skin or soft tissue infections of less than one week’s duration had demographic and historical data collected; a wound culture was also taken. If Staphylococcus aureus was isolated, it was further evaluated by the Centers for Disease Control and Prevention (CDC) to characterize antibiotic resistance patterns, toxin production, and the type of staphylococcal cassette chromosome present.
A total of 422 patients were enrolled, with S. aureus isolated in 320 patients (76%). Of those with isolated S. aureus, 78% had MRSA (59% of the total patients enrolled). The individual site prevalence of MRSA ranged from 15 to 74% and was the predominant etiology of skin and soft tissue infections in 10 of 11 emergency departments. MRSA susceptibilities in this study were 100% to trimethoprim-sulfamethoxazole and rifampin, 95% to clindamycin, 92% to tetracycline, 60% to fluoroquinolones, and 6% to erythromycin. The authors point out that clindamycin resistance in one center was 60%; thus, individual site resistance patterns may differ significantly. Treatment data was available for 406 of the 422 patients, with the majority of those treated with incision, drainage, and antibiotics. In 100 of the 175 MRSA patients treated with antibiotics, the choice of agent was discordant with susceptibility patterns. The authors were able to contact 248 patients between two and three weeks after their visits and, of those contacted, 96% reported resolution or improvement of the wound.
Using multivariate logistic-regression analyses, the authors identified several potential risk factors for MRSA infection. These included use of any antibiotic in the past month, underlying illness, history of MRSA infection, close contact with someone with similar infection, and reported spider bite. Interestingly, being a healthcare worker, living in a long-term care facility, and being hospitalized in the past year were not shown to be significant risk factors in this study.
The results of this study highlight the emerging difficulty, which continues to evolve, with antibiotic resistance patterns. The healthcare community must be vigilant to new entities that challenge the traditional views of antibiotic resistance patterns. The high rate of community-acquired MRSA skin and soft tissue infection demonstrated in this study, in addition to the large percentage of patients prescribed antibiotics that were resistant for the strain involved, emphasizes the need to reconsider the empiric antibiotic choices for this patient population. The variability in regional resistance patterns further complicates the issue. Given the high prevalence of MRSA skin and soft tissue infections reported in this study, use of routine wound cultures appears prudent, as does the need for effective follow-up strategies for alteration of antibiotic choice if necessary. At an institutional level, development of surveillance and isolation strategies for community-acquired MRSA should be considered.