Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections

Methicillin-resistant Staphylococcus aureus (MRSA) has long remained the typical exclusively nosocomial pathogen, allowing using betalactam agents as first line presumptive treatment for severe community-associated infections in which MRSA was not taken into account. The situation dramatically changed with the simultaneous emergence of several strains of community-acquired MRSA in Australia, Europe and in North America. Although these clones clearly emerged from independent ancestors, they present almost invariably with two remarkable features, rarely found in other MRSA clones: (i) methicillin-resistance genes are harboured on a small size staphylococcal cassette chromosome (SCCmec type IV); (ii) they are all transfected by a phage carrying Panton-Valentine leukocidin (PVL) genes. Since the early 2000, a specific clonal group, USA300, spread spectacularly all over North America. A great number of publications documented (i) the unprecedented success of its dissemination in many settings; (ii) its virulence, illustrated by the description of invasive diseases not encountered thus far with traditional clones of hospital-associated MRSA (e.g. necrotizing pneumonia in immunocompetent patients). In Europe, where community-acquired MRSA isolates mainly belong to the ST80 clonal group, its incidence has remained low, thus far. However, cautious surveillance and prompt responses are required if we are to avoid the public health scourge created by the emergence of community-associated MRSA in North America. (C) 2010 Elsevier Masson SAS. All rights reserved.