Infective endocarditis: one in fifty blood cultures were contaminated.

Clinical bottom line (level 4)

  1. At least 2% of positive blood cultures were contaminants.
Wilson et al: Journal of Clinical Microbiology 1975; 2: 94-95
Expires July 2003

The study

Case series with objective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: infectious disease clinic, university hospital, USA

240 patients (aged ?, ?% male) undergoing general medical examination

Excluded if
  • poor oral hygiene
  • clinical laboratory evidence of infection
  • not fasted overnight





    • Outcomes studied:
  • no apparent infection

    • Blood was collected with sterile syringe and needle by members of an experienced venipuncture team; the skin was prepared with povidone-iodine. Cultures were discarded after a total of 14 days of incubation if they were negative macroscopically.

    The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)
    no apparent infection ? 5/240 2.1%
    (0.28% to 2.9%)

    • Staphylococcus epidermis was isolated from four patients and Alcaligenes Faecalis from one- probably skin contaminants.
    • Ratio of number of blood cultures positive to total number of blood culture bottles was 1:2 in all five cases.

    Citation

    1. Wilson WR, et al: Incidence of bacteraemia in adults without infection. Journal of Clinical Microbiology 1975; 2: 94-95
    Search Terms: bacteraemia, blood cultures and contamination
    Contributor: Sumit Dhingra, Carl Heneghan and Chris Ball, July 2000
    Reviewer:

    Clinical Question.
    Patient suspected endocarditis, positive blood culture
    Intervention or Exposure prevalence
    Outcome false positive blood cultures, contaminated blood cultures