β LACTA testing may not improve treatment decisions made with MALDI-TOF MS-informed antimicrobial stewardship advice for patients with Gram-negative bacteraemia: a prospective comparative study.

PURPOSE: The aim of this study was to assess if use of the β LACTA test (BLT) for extended-spectrum beta-lactamase (ESBL) detection and/or early bacterial identification by mass spectrometry (MALDI-TOF MS) improves therapeutic decision-making when combined with advice from the antimicrobial stewardship team (AMST) for the management of Gram-negative bacillary (GNB) bacteraemia.

METHODS: Prospective observational theoretical study that included patients with GNB bacteraemia during a 6-month period. We compared, against the antimicrobial choice of the local AMST as informed of the Gram-stain result, a hypothetical choice, i.e. one AMST would have made had it been informed of the MALDI-TOF MS results only (option H) with the actual choice AMST made after being informed of the combined MALDI-TOF MS and BLT results (option A).Results/Key findings. A total of 131 episodes of GNB bacteraemia were included. Options H and A led to virtually the same rate of efficient antimicrobial therapy (in 120/131 and 123/131 episodes, respectively, P=0.63). Compared to the gold standard, options H and A did not lead to a significant reduction of carbapenem prescription (9/131, 6/131 and 12/131, P=0.57 and P=0.65, respectively).

CONCLUSIONS: Under our test conditions, BLT, when used in conjunction with MALDI-TOF MS and AMST advice, did not allow a significant optimization of the antimicrobial prescription made on the basis AMST advice only. However, the impact of BLT should be evaluated in a population with high prevalence of ESBL-producing Enterobacteriaceae and/or when treatment choices are not made by infectious disease specialists.