Abstract
In Europe, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have been caused predominantly by isolates belonging to the "European CA-MRSA" clone (sequence type 80, staphylococcal cassette chromosome mec type IV). In this study, the epidemiology of European CA-MRSA was investigated on a nationwide scale, covering the period from 1993 to 2004. Denmark has been a low-prevalence country regarding MRSA since the mid-1970s but has experienced an increase in the number of new MRSA cases in recent years. Our results show that European CA-MRSA contributed to this increase. The isolates primarily caused skin and soft tissue infections (SSTIs) in patients outside hospitals, and transmission between household members was the predominant mode of spread. Although some of the isolates were found in hospitalized patients, nosocomial transmission seemed likely in only one instance, pointing to endogenous infections as an important factor. Compared to the CA-MRSA clone most common in the United States (USA300), the European CA-MRSA clone seems less well adapted to persist in hospital environments. Patients with a recent history of travel or family relation to the Mediterranean or Middle East were highly overrepresented. The epidemiological data indicated that the European CA-MRSA isolates were introduced into Denmark on multiple occasions, paralleled by an increasing level of genetic diversity of the isolates found during the study period. European CA-MRSA has previously been described as a rather uniform clone. However, we found pronounced, diverse pulsed-field gel electrophoresis subtypes, staphylococcal protein A gene (spa) types, and susceptibility patterns.