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What are the critical steps in processing blood cultures? A prospective audit evaluating current practice of reporting blood cultures in a centralised laboratory serving secondary care hospitals
  1. Manjula Meda1,
  2. James Clayton2,
  3. Reela Varghese2,
  4. Jayakeerthi Rangaiah3,
  5. Clive Grundy3,
  6. Farnaz Dashti3,
  7. David Garner1,
  8. Katherine Groves1,
  9. Karen Fitzmaurice1,
  10. E Hutley1
  1. 1Department of Microbiology, Frimley Park Hospital, Frimley, UK
  2. 2Department of Microbiology, Royal Surrey County Hospital, Guildford, UK
  3. 3Department of Microbiology, St. Peter's Hospital, Chertsey, UK
  1. Correspondence to Dr Manjula Meda, Department of Microbiology, Frimley Park Hospital, Frimley GU16 7UJ, UK; manjula.meda{at}fhft.nhs.uk

Abstract

Aims To assess current procedures of processing positive blood cultures against national standards with an aim to evaluate its clinical impact and to determine the utility of currently available rapid identification and susceptibility tests in processing of blood cultures.

Methods Blood cultures from three secondary care hospitals, processed at a centralised laboratory, were prospectively audited. Data regarding processing times, communication with prescribers, changes to patient management and mortality within 30 days of a significant blood culture were collected in a preplanned pro forma for a 4-week period.

Results Of 2206 blood cultures, 211 positive blood cultures flagged positive. Sixty-nine (3.1%) of all cultures were considered to be contaminated. Fifty per cent of blood cultures that flagged positive had a Gram stain reported within 2 hours. Two (0.99%) patients with a significant bacteraemia had escalation of antimicrobial treatment at the point of reporting the Gram stain that was subsequently deemed necessary once sensitivity results were known. Most common intervention was de-escalation of therapy for Gram-positive organisms at the point of availability of pathogen identification (25.6% in Gram positive vs 10% in Gram negative; p=0.012). For Gram-negative organisms, the most common intervention was de-escalation of therapy at the point of availability of sensitivity results (43% in Gram negatives vs 17.9% in Gram positive; p=0.0097). Overall mortality within 30 days of a positive blood culture was 10.9% (23/211). Antibiotic resistance may have contributed to mortality in four of these patients (three Gram negative and one Gram positive).

Conclusion Gram stain result had the least impact on antibiotic treatment interventions (escalation or de-escalation). Tests that improve identification time for Gram-positive pathogens and sensitivity time for Gram-negative pathogens had the greatest impact in making significant changes to antimicrobial treatment.

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Footnotes

  • Handling editor Slade Jensen

  • Contributors EH conceptualised the study. EH, JC and MM were involved in the design of the study. All authors contributed to acquisition, planning, conduct, reporting and critical revision of study. MM analysed and interpreted data and drafted the work. All authors have approved the final draft of the study and fully agree to its contents.

  • Competing interests None.

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

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