Impact of Direct Antimicrobial Susceptibility Testing on Respiratory Sample of Intensive Care Patient With Suspected VAP

Plain-language summary

Inappropriate antibiotic therapy in ventilator-associated pneumonia (VAP) is associated with increased mortality. The international guidelines recommend using broad spectrum antimicrobials especially in patients who received previous antimicrobials, with risk factors of muti-drug resistant (MDR) VAP or after 5 days of mechanical ventilation. Using broad-spectrum antibiotics for 48h until the results of conventional cultures and antimicrobial susceptibility testing (AST) are available, may promote the emergence of drug-resistant bacteria. Exposure to imipenem, as short as 1 to 3 days, is associated with a 5-fold increase in the risk of imipenem resistance in the gut microbiota of ICU patients (Armand-Lefevre AAC 2013). Performing AST directly on clinical respiratory samples would hasten the process by at least 24h. The diagnostic performance of a rapid method combining mass spectrometry and direct AST \[DAST\] are previously analyzed, and compared it with the conventional method (mass spectrometry with conventional AST \[CAST\]) and its potential impact was assessed on antimicrobial use in 85 patients (Le DORZE M et al - Clin. Microbiol. Infect. 2015). The results produced by the dast were useable in 85,9% of the cases and the sensitivity and negative predictive values of DAST were 100% for all antibiotics tested, except gentamicin (97.1% \[95%CI = 93.3-101\] and 97.4% \[93.7-101\], respectively) and amikacin (88.9% \[81.7-96.1\] and 96.4% \[92.1-100.7\], respectively), compared with CAST. Specificity and positive predictive values ranged from 82.9 (74.2-91.5) to 100%, and from 86.4 (78.5-94.2) to 100%, respectively. If results had been reported to the clinicians, that DAST would have saved carbapenem prescription in 17 cases (22%) and would have allowed immediate narrow spectrum antimicrobials in 35/85 (41.2%) cases. But, the benefit of DAST was based on a simulation and should be now tested in a randomized fashion. This project is a prospective multicenter study. The hypothesis is that, DAST compared to CAST, would increase the number of adequate antimicrobial therapy within 24 hours in case of late VAP (\> 5 days under mechanical ventilation) with Gram negative bacilli (GNB) in IC patients while sparing carbapenems (imipenem and meropenem). The primary objective is to determine the impact of a strategy using DAST on the rate of day1 adequate therapy without carbapenems in case of late VAP due to GNB.

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