Zero tolerance for healthcare-associated MRSA bacteraemia: is it realistic?
BACKGROUND
The term 'zero tolerance' has recently been applied to healthcare-associated infections, implying that such events are always preventable. This may not be the case for healthcare-associated infections such as methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia.


METHODS
We combined information from an epidemiological investigation and bacterial whole-genome sequencing to evaluate a cluster of five MRSA bacteraemia episodes in four patients in a specialist hepatology unit.


RESULTS
The five MRSA bacteraemia isolates were highly related by multilocus sequence type (ST) (four isolates were ST22 and one isolate was a single-locus variant, ST2046). Whole-genome sequencing demonstrated unequivocally that the bacteraemia cases were unrelated. Placing the MRSA bacteraemia isolates within a local and global phylogenetic tree of MRSA ST22 genomes demonstrated that the five bacteraemia isolates were highly diverse. This was consistent with the acquisition and importation of MRSA from the wider referral network. Analysis of MRSA carriage and disease in patients within the hepatology service demonstrated a higher risk of both initial MRSA acquisition compared with the nephrology service and a higher risk of progression from MRSA carriage to bacteraemia, compared with patients in nephrology or geriatric services. A root cause analysis failed to reveal any mechanism by which three of five MRSA bacteraemia episodes could have been prevented.


CONCLUSIONS
This study illustrates the complex nature of MRSA carriage and bacteraemia in patients in a specialized hepatology unit. Despite numerous ongoing interventions to prevent MRSA bacteraemia in healthcare settings, these are unlikely to result in a zero incidence in referral centres that treat highly complex patients.
Department of Medicine, University of Cambridge, Cambridge, UK Department of Microbiology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK Public Health England, Clinical Microbiology and Public Health Laboratory, Cambridge, UK et317@medschl.cam.ac.uk.
M Estée
ME
Török
Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK.
Simon R
SR
Harris
Department of Medicine, University of Cambridge, Cambridge, UK Public Health England, Clinical Microbiology and Public Health Laboratory, Cambridge, UK.
Edward J P
EJ
Cartwright
Department of Medicine, University of Cambridge, Cambridge, UK.
Kathy E
KE
Raven
Department of Microbiology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK Public Health England, Clinical Microbiology and Public Health Laboratory, Cambridge, UK.
Nicholas M
NM
Brown
Department of Medicine, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
Michael E D
ME
Allison
Department of Microbiology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
Daniel
D
Greaves
Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK.
Michael A
MA
Quail
Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand.
Direk
D
Limmathurotsakul
Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK.
Matthew T G
MT
Holden
Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK.
Julian
J
Parkhill
Department of Medicine, University of Cambridge, Cambridge, UK Department of Microbiology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK Public Health England, Clinical Microbiology and Public Health Laboratory, Cambridge, UK Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok, Thailand.
Sharon J
SJ
Peacock
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016470:Bacteremia / Q000382:microbiology / Q000401:mortality* / Q000517:prevention & control; D015373:Bacterial Typing Techniques; D001483:Base Sequence; D003428:Cross Infection / Q000382:microbiology / Q000517:prevention & control*; D004269:DNA, Bacterial / Q000235:genetics; D003695:Delivery of Health Care / Q000592:standards*; D004196:Disease Outbreaks; D058625:End Stage Liver Disease / Q000382:microbiology; D006801:Humans; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000382:microbiology / Q000517:prevention & control* / Q000635:transmission*
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial
methicillin-resistant Staphylococcus aureus; outbreak; whole-genome sequencing