Cath Lab Digest

Given the challenges of hospital-acquired strains as well as the emergence of community-acquired strains of MRSA, this author discusses clinical, practical and medicolegal aspects of the diagnosis and treatment of this condition.

Staphylococcal organisms are the most common cause of hospital-acquired infections and postoperative infections. Staphylococcal organisms are also the most common bacteria in diabetic foot infections and community-acquired infections.

   Many staphylococcal infections due to methicillin resistant Staphylococcus aureus (MRSA) result in greater morbidity and mortality. This is due to delays in recognition of MRSA as the infecting organism, which subsequently lead to a delay in the initiation of appropriate antibiotic therapy for MRSA. While MRSA is frequently regarded as a more virulent organism, initial therapy offering coverage for MRSA reduces the incidence of significant pathology associated with this organism. In general, one should consider all infection as resulting from MRSA until proven otherwise.

   The medical history may raise suspicion of the predisposition of patients to MRSA infection. One may note MRSA with increasing frequency in patients with chronic wounds, dialysis patients, immunocompromised patients or patients who are or have been in extended care facilities, hospitals, skilled nursing facility (SNF) units or an ICU. In addition, physicians may have a heightened index of suspicion of MRSA in: those exposed to prior prolonged antibiotic therapy; those with surgical site infections, particularly those who have retained hardware; patients with osteomyelitis; or patients with bacteremia and sepsis.

Community-Acquired MRSA: What You Should Know

There has also been a rise of community-acquired MRSA. Community-acquired MRSA may account for as many as 60 to 70 percent of staphylococcal infections.¹ Community-acquired MRSA organisms frequently contain the Panton-Valentine leukocidin, leading to abscess formation and necrosis due to the destruction of leukocytes. Community-acquired MRSA occurs with greater frequency in prisoners, homosexuals and those participating in contact sports.

   One must consider certain groups of patients as potentially infected with community-acquired MRSA until proven otherwise. These patients include those with shorter hospital stays, patients on parenteral antibiotic therapy, patients in the community using broad-spectrum drugs, those with a history of intravenous drug use, and those with exposure to MRSA colonized individuals.

   In each of the above instances, empiric treatment of an infection should include coverage for MRSA.

   Community-acquired MRSA infection is frequently characterized by a necrotic wound center. A delay in diagnosis of MRSA is inevitable without a proper culture. Fortunately, many abscesses secondary to MRSA infection respond to incision and drainage, even in the absence of appropriate antibiotic therapy. Bear in mind that MRSA infection may be misdiagnosed as a spider or arachnoid bite. In a 2006 study, researchers found that MRSA accounted for 72 percent of nearly 400 cases of community-onset skin and soft tissue infection.²

   Data USA Surveillance Network, a cooperative of 296 laboratories in nine census regions, has established an incidence of 57.8 percent for MRSA soft tissue and skin infections.³ The network noted no difference in community versus hospital-acquired infections and ICU strains were the most resistant. The highest reported rates of MRSA occur in the central United States and the lowest rates are reported in the New England and mid-Atlantic areas. This study, conducted between 2005 and 2007, noted that linezolid (Zyvox, Pfizer) resistance continues to be rare and that trimethoprim/sulfamethoxazole (Bactrim, Roche and Septra, GlaxoSmithKline) continues to demonstrate good activity against MRSA.