Diagnostic and prognostic value of time to positivity in blood cultures. An opinion paper.

Time to positivity (TTP) refers to the duration required for a microbiological culture test to indicate a positive result, marking the onset of detectable bacterial or fungal growth in the sample. Numerous variables, including patient characteristics, infection source, former antimicrobial therapy, blood sample volume, and sample transportation time can influence the value of TTP. Several studies have been conducted on bloodstream infections, whereas studies on the clinical significance of yeast TTP are quite limited in the literature. Furthermore, many studies are retrospective and have a small sample size. In this opinion paper, we have formulated some questions and attempted to provide answers based on the available literature and our perspective. The objective of this opinion paper is to summarise current knowledge based on the literature, aiming to offer a critical perspective, particularly on aspects with weaker evidence, which could guide future studies in this area. We believe that TTP of blood cultures appears to exhibit considerable potential and may prove to be a valuable tool in clinical practice for estimating patient mortality risk and guiding antimicrobial therapy choices. Topics discussed include the diagnostic and prognostic role of TTP in Gram-positive and Gram-negative bacteremias and in candidemias, and the significance of differential time to positivity (DTTP). In summary, our opinion is that, based on the available literature, it is not possible to determine whether TTP provides prognostic information, particularly concerning candidemia. Therefore, clinical decisions cannot be systematically based on this parameter.