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

Methods

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 …