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Community-Acquired MRSA: Unraveling Its Disease Spectrum

Community-acquired MRSA infections are increasingly common -- and are becoming increasingly serious.

How widespread are community-acquired infections due to emerging methicillin-resistant Staphylococcus aureus (MRSA) strains, and are these strains responsible for changes in the clinical spectrum of staphylococcal disease? Two reports now begin to supply some answers.

Fridkin and colleagues studied infections identified by a specialized MRSA surveillance project in Atlanta, Baltimore, and several regions of Minnesota. During 2001 and 2002, 2107 MRSA isolates (8%-20% of all MRSA isolates collected) were classified as community-acquired; 1647 of them were associated with clinical illness. Annual incidence of community-associated MRSA disease varied by site, ranging from 18.0 to 25.7 cases per 100,000 population. Rates were significantly higher among children <2 years old than among individuals 2 and, in Atlanta, among blacks than whites. Of the 1647 disease episodes, 77% were infections of skin and soft tissue, and 6% were invasive infections (e.g., bacteremia, septic arthritis, osteomyelitis). Twenty-three percent of patients required hospitalization for MRSA disease; of these, 10% required intensive care. Only one patient died as a result of MRSA infection. Antimicrobial therapy (typically, a ß-lactam) inactive against the infecting strain was given to 73% of patients, with no discernible adverse effects on outcomes among patients interviewed (all of whom had skin or soft-tissue infections). Although patients with community-acquired MRSA infections, by definition, lacked established risk factors for MRSA infection, 45% had underlying conditions or circumstances associated with skin infections (see Journal Watch Infectious Diseases Feb 28 2005) or suggesting contact with the healthcare system.

Miller and colleagues described 14 cases of surgically confirmed necrotizing fasciitis due to community-acquired MRSA, occurring in Los Angeles from January 15, 2003, through April 15, 2004. Necrotizing fasciitis, typically caused by group A streptococcus, Clostridium perfringens, or a mixture of aerobic and anaerobic organisms, had been attributed to a monomicrobial MRSA infection before in only one patient, following surgery. Of the 14 patients (median age, 46 years), all underwent at least one surgical procedure, 10 required intensive care, and 3 had reconstructive plastic surgery; all survived. In most patients, disease onset seemed less acute than in classic necrotizing fasciitis, with symptoms present an average of 6 days before hospitalization. Blood cultures were positive in 4 of 10 patients. All but 4 patients had coexisting conditions or risk factors, including current or past injection-drug use (6 patients), hospitalization within the previous year (6), homelessness (4), a seizure disorder (3), diabetes (3), chronic hepatitis C (3), or earlier MRSA infection (3). Wound cultures from 12 of the 14 patients grew only MRSA. All MRSA isolates were susceptible to clindamycin, trimethoprim-sulfamethoxazole, vancomycin, gentamicin, and rifampin. The five isolates available for analysis belonged to the same genotype and carried Panton-Valentine leukocidin, lukD, and lukE toxin genes.

Comment: Community-acquired MRSA infections are increasing. Although these reports do not address the proportion of community-associated staphylococcal infections that are caused by MRSA strains not originating in hospitals, an editorialist suggests that in Atlanta this figure may exceed 5%. Community-acquired MRSA must be added to the monomicrobial etiologies of necrotizing fasciitis, and clinicians must be alert to the need for antimicrobial therapy directed against these strains, as well as to the necessity for surgical intervention. Although the development of necrotizing fasciitis due to community-acquired MRSA is disturbing, it should be noted that 9 of the 14 reported patients either had been hospitalized within the previous year or had a history of MRSA infection.

— Neil R. Blacklow, MD

Published in Journal Watch Infectious Diseases April 22, 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-acquired MRSA -- Resistance and virulence converge. N Engl J Med 2005 Apr 7; 352:1485-7.

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