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Over 18 h to positivity in the BacT/ALERT system with clustered Gram-positive cocci is highly predictive of coagulase-negative staphylococci
  1. Ricardo A Zimerman,
  2. Denise P Machado,
  3. Caroline C Constante,
  4. Afonso L Barth,
  5. Luciano Z Goldani
  1. Section of Infectious Diseases and Microbiology Unit, Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
  1. Correspondence to:
 Dr L Z Goldani
 Serviço de Infectologia, Hospital de Clínicas de Porto Alegre, Ramiro Barcelos 2350, 900035-003, Porto Alegre, RS, Brazil; lgoldani{at}

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Coagulase-negative staphylococci (CoNS) are the most common bacteria isolated from blood cultures, but a great proportion of them are most likely contaminants.1,2 On the other hand, one single positive blood culture for Staphylococcus aureus is usually sufficient to diagnose bacteraemia. Therefore, a rapid method of differentiating CoNS from S aureus would assist in the clinical decision on starting antimicrobial treatment in a timely manner. As many laboratories routinely process blood culture bottles in automated systems that record time to positivity (TTP) and this information is readily available along with the Gram-smear results, we assessed the predictive value of TTP for the exclusion of S aureus in the setting of a positive result for clustered Gram-positive cocci.1,3,4


For this purpose, we retrospectively analysed all blood cultures collected from patients between January 2005 and February 2006 in a large university teaching hospital. In our hospital, we routinely collected two blood cultures for every patient, each one consisting of a single BacT/ALERT FA aerobic bottle. The sets …

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  • Published Online First 13 February 2007

  • Competing interests: None declared.