Objective: Antibiotic exposure and timing of pneumonia onset influence ventilator-associated pneumonia (VAP) isolates. The first goal of this investigation was to evaluate whether trauma also influences prevalence of microorganisms.
Design: A retrospective, single-center, observational cohort study.
Setting: Multidisciplinary teaching ICU.
Patients: Adult patients requiring mechanical ventilation identified as having VAP.
Interventions: Retrospective evaluation of a prospective manual database.
Measurements and main results: VAP isolates in a multidisciplinary ICU documented by quantitative respiratory cultures and recorded in a 42-month database were compared, based on the presence or absence of trauma. Causative microorganisms were classified in four groups, based on mechanical ventilation duration (> 5 days), and previous antibiotic exposure. One hundred eighty-three patients developed 196 episodes of VAP (98 trauma). Methicillin-sensitive Staphylococcus aureus (MSSA) was more frequent (34.5% vs. 11.5%, p < 0.01) in trauma, whereas methicillin-resistant Staphylococcus aureus (MRSA) was more frequent (2% vs. 11.5%, p < 0.01) in non-trauma. No significant differences were found between trauma and non-trauma patients regarding prevalence of other microorganisms. In trauma patients, MSSA episodes were equally distributed between early- and late-onset VAP (51% vs. 49%), but no MRSA episode occurred in the early-onset group.
Conclusions: Trauma influences the microbiology of pneumonia and it should be considered in the initial antibiotic regimen choice. Our data demonstrate that patients with trauma had a higher prevalence of MSSA, but the overall prevalence was sufficiently high to warrant S. aureus coverage for both groups. On the other hand, since no MRSA was isolated during the first 10 days of mechanical ventilation on trauma patients, MRSA coverage in these patients becomes necessary only 10 days after admission.