Clinical and microbiological characteristics of communityacquired methicillin-resistant Staphylococcus aureus pneumonia

Methicillin-resistant Staphylococcus aureus (MRSA) infections now occur in healthy adults in community settings. We searched the PubMed database to identify relevant articles on the clinical presentation, epidemiology, virulence, and treatment of community-acquired MRSA (CA-MRSA) infections, including pneumonia. This information was summarized in a narrative review.MRSA infections cause approximately 30 infections per 100,000 people per year in the USA, and twenty percent of these infections are secondary to CA-MRSA. These community-acquired infections often involve the skin and subcutaneous tissue but can also involve visceral tissues such as the lung and bone. The overall mortality in patients with invasive disease is approximately 10%; it approaches 50% in patients with pneumonia. The bacterial isolates from these infections have the staphylococcal chromosome cassette mec types 4 and 5. This genetic characteristic produces beta-lactam resistance and helps distinguish these isolates from hospital- acquired MRSA, which usually have mec types 1-3. Some CA-MRSA isolates release the Panton-Valentine leukocidin (PVL), which causes neutropenia and tissue necrosis; other toxins also contribute to the virulence of these infections. Empiric therapy should include vancomycin or linezolid. CA-MRSA infections can have fulminant courses and high mortality rates. Physicians should consider these infections as possible emergencies with a high risk for organ system failure and shock.