Incidence and outcome of polymicrobial ventilator-associated pneumonia

Study objective: To determine the epidemiology, and outcome of poly-microbial ventilator-associated pneumonia (VAP). Setting: Two ICUs (18 and 17 beds) in a university hospital. Design and patients: We undertook a 16-month study of 124 patients in whom a first episode of VAP had been diagnosed. Patients in whom there was a suspicion of clinical or radiologic VAP underwent bronchoscopy, and VAP was confirmed by the presence of at least two of the following criteria: greater than or equal to 2% of cells with intracellular bacteria found on direct examination of BAL fluid (BALF); protected-specimen brush sample culture with greater than or equal to 10(3) cfu/mL; or BALF culture with greater than or equal to 10(4) cfu/mL. Results: Monomicrobial infections were diagnosed in 65 patients (52%), and polymicrobial infections were diagnosed in 59 patients (48%). Two different bacteria were isolated in 42 patients (34%), three different bacteria were isolated in 10 patients (8%), and four different bacteria were isolated in 7 patients (6%). Patients' clinical characteristics at ICU admission and on the day of bronchoscopy were similar, particularly the prior duration of mechanical ventilation (MV), the type of ICU admission, disease severity scores, and antibiotic therapy received before VAP was diagnosed. The percentages of nonfermenting, Gram-negative bacilli and methicillin-resistant staphylococci involved in monomicrobial and polymicrobial episodes were similar. Furthermore, no significant difference was detected in outcome parameters, specifically in the mortality rate at 30 days, the ICU mortality rate, the duration of MV, and the rate of infection relapse. Conclusion: In our study population, the epidemiology and outcomes of patients with monomicrobial and poly-microbial VAP did not differ significantly.