Emergence of an Epidemic Clone of Community-Associated Methicillin-Resistant Panton-Valentine Leucocidin-Negative Staphylococcus aureus in Cystic Fibrosis Patient Populations

Abstract

The article by Moroney et al. (3) documents the increased prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains in different patient populations. Most of the CA-MRSA strains characterized by carriage of staphylococcal cassette chromosome mec (SCCmec) type IV were also positive for the Panton-Valentine leucocidin (PVL) gene 1 (2). However, this gene association is not necessarily indicative of CA-MRSA strains. We analyzed the prevalence and molecular epidemiology of MRSA from the airways of cystic fibrosis (CF) patients in an Italian multicenter study. One hundred eighty-one (7.6%) out of 2,362 CF patients attending 9 Italian CF centers were infected with MRSA. A high prevalence (36%) of SCCmec IV (suggestive of CA-MRSA strains) was found (5). Pulsed-field gel electrophoresis analysis showed a single MRSA clone colonizing 31 patients in 6 centers. Twenty-four out of 31 strains (77.4%) revealed SCCmec type IV, mostly associated with CA-MRSA. All the SCCmec type IV MRSA isolates belonging to the epidemic clone were negative for the PVL genes, as reported by other authors (4). The high prevalence of MRSA strains, suggestive of CA-MRSA in a patient population considered at risk for hospital-associated (HA)-MRSA acquisition, is worrisome evidence supporting current opinions that CA-MRSA strains are replacing HA-MRSA strains in health care settings (1, 6). The interesting question of whether the CA-MRSA clone infected the CF patients in the community or whether the patients acquired the clone in the hospital which they attended regularly is unclear and needs to be further studied.