Emergence of community-acquired meticillin-resistant Staphylococcus aureus strain USA300 as a cause of necrotising community-onset pneumonia.

Meticillin-resistant Staphylococcus aureus (MRSA), usually known as a nosocomial pathogen, has emerged as the predominant cause of skin and soft-tissue infections in many communities. Concurrent with the emergence of community-acquired MRSA (CA-MRSA), there have been increasing numbers of reports of community-acquired necrotising pneumonia in young patients and others without the classic health-care-associated risk factors. Community-onset necrotising pneumonia due to CA-MRSA is now recognised as an emerging clinical entity with distinctive clinical features and substantial morbidity and mortality. A viral prodrome (eg, influenza or influenza-like illness) followed by acute onset of shortness of breath, sepsis, and haemoptysis is the most frequent clinical presentation. The best treatment of this partly toxin-mediated disease has not been clearly defined. Whereas cases of CA-MRSA pneumonia have now been reported from almost every continent, the overall burden of disease of this emerging syndrome remains incompletely described. We report two related cases of community-onset pneumonia due to the MRSA USA300 genotype and review the literature regarding the emergence of CA-MRSA pneumonia.