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Infectious diseases
Research
Decline of meticillin-resistant Staphylococcus aureus in Oxfordshire hospitals is strain-specific and preceded infection-control intensification
  1. David H Wyllie1,
  2. A Sarah Walker1,2,
  3. Ruth Miller1,
  4. Catrin Moore3,
  5. Susan R Williamson1,
  6. Iryna Schlackow1,
  7. John M Finney1,
  8. Lily O'Connor1,
  9. Tim E A Peto1,
  10. Derrick W Crook1
  1. 1Oxford Biomedical Research Centre, John Radcliffe Hospital, Oxford, UK
  2. 2MRC Clinical Trials Unit, London, UK
  3. 3Mahidol-Oxford Tropical Medicine Research Unit (MORU), Bangkok, Thailand
  1. Correspondence to Dr David H Wyllie; david.wyllie{at}ndm.ox.ac.uk

Abstract

Background In the past, strains of Staphylococcus aureus have evolved, expanded, made a marked clinical impact and then disappeared over several years. Faced with rising meticillin-resistant S aureus (MRSA) rates, UK government-supported infection control interventions were rolled out in Oxford Radcliffe Hospitals NHS Trust from 2006 onwards.

Methods Using an electronic Database, the authors identified isolation of MRS among 611 434 hospital inpatients admitted to acute hospitals in Oxford, UK, 1 April 1998 to 30 June 2010. Isolation rates were modelled using segmented negative binomial regression for three groups of isolates: from blood cultures, from samples suggesting invasion (eg, cerebrospinal fluid, joint fluid, pus samples) and from surface swabs (eg, from wounds).

Findings MRSA isolation rates rose rapidly from 1998 to the end of 2003 (annual increase from blood cultures 23%, 95% CI 16% to 30%), and then declined. The decline accelerated from mid-2006 onwards (annual decrease post-2006 38% from blood cultures, 95% CI 29% to 45%, p=0.003 vs previous decline). Rates of meticillin-sensitive S aureus changed little by comparison, with no evidence for declines 2006 onward (p=0.40); by 2010, sensitive S aureus was far more common than MRSA (blood cultures: 2.9 vs 0.25; invasive samples 14.7 vs 2.0 per 10 000 bedstays). Interestingly, trends in isolation of erythromycin-sensitive and resistant MRSA differed. Erythromycin-sensitive strains rose significantly faster (eg, from blood cultures p=0.002), and declined significantly more slowly (p=0.002), than erythromycin-resistant strains (global p<0.0001). Bacterial typing suggests this reflects differential spread of two major UK MRSA strains (ST22/36), ST36 having declined markedly 2006–2010, with ST22 becoming the dominant MRSA strain.

Conclusions MRSA isolation rates were falling before recent intensification of infection-control measures. This, together with strain-specific changes in MRSA isolation, strongly suggests that incompletely understood biological factors are responsible for the much recent variation in MRSA isolation. A major, mainly meticillin-sensitive, S aureus burden remains.

  • Microbiology
  • bacteriology
  • microbiology
  • epidemiology
  • genetics
  • infectious diseases
  • health informatics
  • information management
  • information technology
  • worldwide web technology

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

https://doi.org/10.1136/bmjopen-2011-000160

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    Footnotes

    • To cite: Wyllie DH, Walker AS, Miller R, et al. Decline of meticillin-resistant Staphylococcus aureus in Oxfordshire hospitals is strain-specific and preceded infection-control intensification. BMJ Open 2011;1:e000160. doi:10.1136/bmjopen-2011-000160

    • Funding This article presents independent research commissioned by the National Institute for Health Research (NIHR) under its Oxford Biomedical Research Centre Infection Theme, and the Program Development Grants funding scheme (RP-DG-1108-10125). The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.

    • Competing interests None.

    • Ethical approval Ethics approval was provided by the Oxford Research Ethics Committee and by the National Information Governance Board.

    • Contributors DHW and ASW performed the analyses and wrote the paper. DHW is guarantor. SW and IS performed the analyses; CM and RM genotyped the S aureus strains; DHW and JF constructed the Infection in Oxfordshire Research Database; LOC provided details of infection-control interventions; all authors reviewed the manuscript and critically analysed the work.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement No additional data available.