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New strains of meticillin-resistant Staphylococcus aureus (MRSA) may be associated with changes in rates of disease or clinical presentation. Conventional typing techniques may not detect new clonal variants that underlie changes in epidemiology or clinical phenotype.To investigate the role of clonal variants of MRSA in an outbreak of MRSA bacteraemia at a hospital in England.Bacteraemia isolates of the major UK lineages (EMRSA-15 and -16) from before and after the outbreak were analysed by whole-genome sequencing in the context of epidemiological and clinical data. For comparison, EMRSA-15 and -16 isolates from another hospital in England were sequenced. A clonal variant of EMRSA-16 was identified at the outbreak hospital and a molecular signature test designed to distinguish variant isolates among further EMRSA-16 strains.By whole-genome sequencing, EMRSA-16 isolates during the outbreak showed strikingly low genetic diversity (P < 1 × 10(-6), Monte Carlo test), compared with EMRSA-15 and EMRSA-16 isolates from before the outbreak or the comparator hospital, demonstrating the emergence of a clonal variant. The variant was indistinguishable from the ancestral strain by conventional typing. This clonal variant accounted for 64/72 (89%) of EMRSA-16 bacteraemia isolates at the outbreak hospital from 2006.Evolutionary changes in epidemic MRSA strains not detected by conventional typing may be associated with changes in disease epidemiology. Rapid and affordable technologies for whole-genome sequencing are becoming available with the potential to identify and track the emergence of variants of highly clonal organisms.

Original publication

DOI

10.1016/j.jhin.2013.11.007

Type

Journal article

Journal

The journal of hospital infection

Publication Date

02/2014

Volume

86

Pages

83 - 89

Addresses

Nuffield Department of Clinical Medicine, University of Oxford, John Radcliffe Hospital, Oxford, UK; NIHR Oxford Biomedical Research Centre, John Radcliffe Hospital, Oxford, UK.

Keywords

Humans, Bacteremia, Staphylococcal Infections, Cross Infection, Bacterial Typing Techniques, Cluster Analysis, Disease Outbreaks, Genotype, Genome, Bacterial, Hospitals, England, Genetic Variation, Methicillin-Resistant Staphylococcus aureus, High-Throughput Nucleotide Sequencing, United Kingdom