Emergence of methicillin-resistant Staphylococcus aureus USA300 genotype as a major cause of late-onset nosocomial pneumonia in intensive care patients in the USA

Abstract

To compare demographic and clinical characteristics, and methicillin-resistant Staphylococcus aureus (MRSA) strain characteristics, in patients with early-onset (EO) and late-onset (LO) MRSA nosocomial pneumonia. This was a retrospective analysis of data from a multicenter observational study of nosocomial pneumonia patients admitted between November 2008 and July 2010. Laboratory analyses performed on MRSA isolates included confirmation of antimicrobial susceptibility and heteroresistance to vancomycin, USA typing, staphylococcal cassette chromosome (SCC) mec typing, and detection of Panton-Valentine leukocidin (PVL) genes. We identified 134 patients; 42 (31%) had EO MRSA pneumonia and 92 (69%) had LO MRSA pneumonia. The patients in the LO group were more likely to have risk factors for multidrug-resistant pathogens (98% vs. 76%, p<0.001). The MRSA USA300 strain was found with equal frequency in the EO and LO groups. Likewise, both groups had similar frequencies of isolates exhibiting PVL and SCCmec type IV. Our findings provide further evidence of the continued migration of community-associated MRSA into the healthcare setting in the USA. MRSA USA300 genotype has emerged as a significant cause of LO nosocomial pneumonia in intensive care units. Appropriate anti-MRSA antimicrobial therapy should be considered for both EO and LO hospital-acquired pneumonia and ventilator-associated pneumonia.