Data for this Review were identified by searches of PubMed and references from relevant articles. Search terms were “community MRSA Europe” and “community MRSA AND [all European countries]”. The search was limited to publications in English up to Dec 4, 2009.
ReviewMolecular epidemiology of community-associated meticillin-resistant Staphylococcus aureus in Europe
Introduction
Meticillin-resistant Staphylococcus aureus (MRSA) is endemic in many hospitals worldwide.1, 2 Previously, MRSA infections were nearly always associated with hospital or health-care contact, but new strains of MRSA have emerged that cause community infection in patients without previous health-care contact.2, 3
New MRSA clones emerge because of acquisition of meticillin resistance by previously susceptible S aureus strains.1, 4 Clinically significant meticillin resistance is conferred by expression of the mecA gene, which encodes a modified penicillin-binding protein (PBP2a or PBP2′) that has low affinity for β-lactam antibiotics and facilitates cell-wall synthesis in the presence of meticillin and other β-lactams.1 The mecA gene is carried on a mobile genetic element, the staphylococcal cassette chromosome (SCCmec).1 SCCmec probably originated in coagulase-negative staphylococci and integrates site-specifically into the S aureus genome.1, 4 A range of SCCmec types, known as I to VII and their variants, have been described and new types continue to emerge.1
Despite the global scale of the problems caused by health-care-associated MRSA, only a small number of major clones have been identified.1, 2, 4 These clones can be characterised by multilocus sequence typing (MLST) and SCCmec type. The five predominant health-care-associated MLST clonal complexes are listed in the panel.
The rate of meticillin resistance in blood isolates of S aureus (mostly health-care-associated MRSA) in European countries ranges from less than 1% in Norway, Sweden, and Denmark and less than 5% in the Netherlands, to more than 40% in Greece and the UK and more than 50% in Malta.5 The wide range of MRSA prevalence in Europe might be associated with the effectiveness of implementation of national antibiotic prescribing and infection control policies.5, 6, 7 Additionally, the dominance of just a few health-care-associated MRSA clones suggests that some strains have particular abilities to survive and transmit in hospital environments and, once they are established in a health system, are difficult to eradicate. The emergence of endemic health-care-associated MRSA in England since 1990, for example, has mainly been caused by the spread of EMRSA-15 (ST22-IV) and EMRSA-16 (ST36-II).8 However, the reasons why some clones are more successful than others have not been established.
MRSA colonisation can persist for months or years9 and, until recently, MRSA infections presenting in the community were usually caused by health-care-associated MRSA strains acquired directly or indirectly during previous hospital or health-care contact.10, 11 In general, however, health-care-associated MRSA has not spread within the community. True community-acquired or associated MRSA infection, caused by strains distinct from health-care-associated MRSA, was first reported as an outbreak of skin and soft-tissue infection in drug users in Detroit, MI, USA, in the early 1980s.12 Community-associated MRSA infections in patients without previous health-care contact began to emerge in the early 1990s in western Australia13 and in US children,14, 15, 16 and in some European countries17, 18, 19 in the late 1990s. Community-associated MRSA infections have since been seen worldwide, with substantial increases in prevalence in the USA,3 where they were the predominant cause of S aureus skin and soft-tissue infections in patients presenting to emergency departments in 2004.20
We review the molecular epidemiology of community-associated MRSA in Europe to identify priorities for future infection control policies.
Section snippets
Characteristics
Health-care-associated MRSA strains usually cause infection in hospitalised, compromised, elderly patients. Community-associated MRSA strains, in common with meticillin-susceptible S aureus, can affect younger, healthy people and can spread readily in community settings.16, 21 Community subsets that are at high risk of infection include injecting drug users,12, 22, 23 Indigenous people,13, 24 prisoners and those of low socioeconomic status,25, 26, 27, 28, 29 men who have sex with men,30 players
Molecular epidemiology
The most useful molecular methods to differentiate community-associated from health-care-associated MRSA are MLST, SCCmec type, sequencing of the repeat regions of the S aureus protein A (spa) type, PVL status, and pulse-field gel electrophoresis (PFGE) profile.62, 63 These methods can be combined to characterise community-associated MRSA clones internationally. As with health-care-associtated MRSA, successful clones of community-associated MRSA are usually associated with specific geographical
Discussion
Accurate ascertainment of the prevalence of community-associated MRSA in Europe is difficult for several reasons. First, most carriers are not infected and therefore are likely to remain undetected. Second, community-associated MRSA colonisation of other body sites in the absence of nasal colonisation is common, so surveys of rates of nasal colonisation will underestimate true prevalence.42, 43 Third, even when infections are present, patients are often treated in community or outpatient
Conclusion
The main burden of MRSA disease in Europe continues to be health-care associated. However, infections with community-associated MRSA are now emerging. Surveillance data are limited, but community-associated MRSA prevalence is much lower than that reported in the USA. There is an urgent need to clarify the prevalence and epidemiology of community-associated MRSA in Europe and to develop systems for identification and control of these organisms in the community, hospitals, and other health-care
Search strategy and selection criteria
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