Severe community-onset pneumonia in healthy adults caused by methicillin-resistant Staphylococcus aureus carrying the Panton-Valentine leukocidin genes

Background. Recent worldwide reports of community- onset skin abscesses, outbreaks of furunculosis, and severe pneumonia associated with methicillin- resistant Staphylococcus aureus ( MRSA) carrying Panton- Valentine leukocidin ( PVL) genes and the staphylococcal cassette chromosome mec ( SCCmec) type IV indicate that MRSA infections are evolving into a community- related problem. The majority of cases reported to date involve skin and soft- tissue infections, with severe pneumonia representing a relatively rare phenomenon. During a 2- month period in the winter of 2003 - 2004, four healthy adults presented to 1 of 2 Baltimore hospitals with severe necrotizing MRSA pneumonia in the absence of typical risk factors for MRSA infection. Methods. Patients' MRSA isolates were characterized by strain typing with use of pulsed- field gel electrophoresis and SCCmec typing with use of a multiplex polymerase chain reaction ( PCR) assay and detection of PVL genes by PCR. Results. All 4 patients' MRSA isolates carried the PVL genes and the SCCmec type IV element and belonged to the USA300 pulsed- field type. These 3 findings are among the typical characteristics of community- onset MRSA strains. In addition, 2 of our patients had concomitant influenza A diagnosed, which likely contributed to the severity of their presentation. Conclusions. To our knowledge, these patients represent the first reported North American adults with severe community- onset MRSA pneumonia caused by strains carrying the PVL genes.