LAUSR

Objective: To determine whether prior antimicrobial therapy, divided in recent or current antibiotic treatment, influences the identification rate and/or the type of causative pathogens in patients with suspected episodes of ventilator‐acquired pneumonia. Design: Monocentric retrospective study. Setting: Intensive car unit in a universitary hospital. Patients: 230 episodes of ventilator‐associated pneumonia with a Clinical Pulmonary Infection Score ≥ 6 were retrospectively evaluated. Based on the antimicrobial treatment regimen, we defined 3 groups: the no antimicrobial treatment group (VAP is suspected in patients that has never received antibiotics during the last 90 days), group 2: the current antimicrobial therapy (VAP is suspected under antimicrobial therapy) and group 3: the recent antimicrobial therapy (VAP is suspected whereas an antimicrobial treatment has been used during the last 90 days but discontinued for >24 h). Intervention: Bacteriologic analysis using a protected distal sampling with microscopic examination, culture and microbial identification using MALDI‐TOF. Measurements and main results: Suspected episodes of VAP were sorted as follow: 70 suspected episodes in the no antimicrobial therapy group, 106 suspected episodes in the current antimicrobial therapy group and 54 suspected episodes in the recent antimicrobial therapy group. The rate of positive culture was significantly lower in the current antimicrobial treatment group (group 2) when compared to the recent (group 3) and to the no antimicrobial treatment groups (group 1) (42%, 68% and 86%, respectively). When compared to the recent antibiotherapy group, we observed that current antibiotherapy was significantly associated with a higher rate of MDR positive culture, mainly due to higher rate of MDR Pseudomonas aeruginosa. Conclusion: In patients with a high probability of VAP, current but not recent antibiotic use is associated with a lower rate of positive culture with a higher proportion of MDR pathogens, mostly MDR Pseudomonas aeruginosa. Highlights:Proportion of multidrug‐resistant pathogens depends on the timing of prior antimicrobial treatmentCurrent but not recent antibiotic use is associated with a lower rate of positive culture with a higher proportion of MDR pathogens, mostly MDR Pseudomonas aeruginosa.Further studies should investigate the usefulness of periodic assessment of lung microbiota.