Abstract:

Objective　 To investigate the significance of time to positivity (TTP) for predicting Staphylococcus aureus (SA), coagulase negative Staphylococcus (CoNS) and methicillin-resistant Staphylococcus aureus (MRSA) in blood culture. Methods　 The TTP for predicting SA and CoNS in blood culture from 2008 to 2012 in Beijing University First Hospital were collected. MRSA and methicillin-susceptible Staphylococcus aureus (MSSA) were judged by their susceptibility to oxacillin. Only the first isolate was included in this study for those repetitively isolated from the same patients. TTP between SA and CoNS and TTP between MRSA and MSSA were compared statistically. Receiver operating characteristic (ROC) curve was used to analyze the diagnosis significance of TTP. Results　 A total of 101 isolates of SA (51 isolates of MRSA and 50 isolates of MSSA) and 253 isolates of CoNS were collected. TTP of SA and CoNS were (16.63±7.47) h and (24.61±11.09) h with statistical significance (P<0.05), and TTP of MRSA and MSSA were (18.22±8.15) h and (15.01±6.40) h with statistical significance (P<0.05). ROC curve showed that TTP≤16.90 h was the cut-off point to differentiate SA and CoNS, and the area under the ROC curve (AUC) was 0.758. TTP>12.58 h was the cut-off point to differentiate MRSA and MSSA, and the AUC was 0.630. Conclusions　 The accuracy of TTP for predicting SA and CoNS is moderate, and the accuracy of TTP for predicting MRSA and MSSA is low.

Key words: Time to positivity, Blood culture, Staphylococcus aureus, Coagulase negative Staphylococcus, Methicillin-resistant Staphylococcus aureus