An Algorithm for Rapid and Low-Cost Detection of Carbapenemases Directly from Positive Blood Cultures Using an Immunochromatographic Test

<b>Background/Objectives</b>: Detection of carbapenemases (KPC, OXA-48, VIM, IMP, NDM) from blood cultures (BCs) by standard methods takes 48-72 h and includes BC seeding, susceptibility testing and carbapenemase detection. Automated qPCR panels provide results in 1 h but are very costly. We aim to evaluate a low-cost and rapid immunochromatographic (IC) test directly from positive BCs using the reference method as a comparator. <b>Methods</b>: Ninety-one positive BCs from real-world patients and sixty-four simulated BCs were included. BC broth was treated with SDS and washed before analysis with the K.N.I.V.O. carbapenemase detection IC test. Discordant results were confirmed through the NG Carba-5 IC test and GeneXpert Carba-R qPCR test. <b>Results</b>: The test detected 100% of the 87 carbapenemase-producing BCs tested (sensitivity: 100% [CI95%: 95.8-100%]). However, 13 BCs generated false positive bands for NDM and/or OXA-48 (specificity: 80.8% [CI95%: 69.5-89.4%). The positive and negative predictive values were 87.0% (CI95%: 80.4-91.6%) and 100% (CI95%: 93.5-100%). Analysis of BCs providing false positive results through both confirmatory tests showed that BCs were negative for these carbapenemases. <b>Conclusions</b>: This is the first evaluation of the K.N.I.V.O. IC test directly from positive BCs, with a pragmatic confirmation algorithm using a second IC test or qPCR in case of NDM or OXA-48, that addresses K.N.I.V.O.'s specificity gap. The main limitation of this work is that confirmatory testing was performed only in false positives. The implementation of the K.N.I.V.O. IC test would contribute to early carbapenemase detection in BCs and is an alternative for low-resource hospitals where qPCR panels are not available.