The effect of prior antimicrobial therapy for community acquired infections on the aetiology of early and late onset ventilator-associated pneumonia in a level I trauma intensive care unit

Abstract

Background: Ventilator-associated pneumonia (VAP) is the most common hospital acquired infection in patients who require mechanical ventilation. Early VAP is associated with community acquired pathogens whereas late VAP involves hospital flora. Based on this premise, a protocol may be formulated for microbiological surveillance and antimicrobial stewardship within a specific intensive care unit (ICU) to ensure appropriate empiric antimicrobial choice. The bacterial flora in VAP may be affected, however, by antimicrobials prescribed during the ICU stay. Aim: The aim of this study was to determine the effect of prior antimicrobial therapy for community acquired infections on aetiology and the susceptibility of bacterial isolates from the first episode of early or late VAP in a trauma intensive care unit.Methods: Endotracheal aspirates (ETAs) were obtained from patients with suspected early and late VAP. All ETAs were processed and interpreted as per the Clinical and Laboratory Standards Institute (CLSI). Patients were divided into two cohorts: those whose injuries had required antimicrobial therapy for community acquired infections and those who were antimicrobial naïve. The effect of prior antimicrobial therapy on bacterial isolates from the first episode of suspected VAP was compared between the two groups.Results: Of 288 patients admitted to the Trauma ICU between January and December 2014, pneumonia was suspected in 91 (31.6%). Of these, 69 (76%) patients were antimicrobial naïve and 22 (24%) had received prior antimicrobial therapy. Early VAP occurred in 31 (45%) patients in the naïve cohort compared to 3 (12.5%) with prior antimicrobial exposure (p = 0.01). Of the early VAP isolates 25 (81%) in the naïve cohort contained community flora, whereas all isolates in those with prior antimicrobial therapy revealed hospital acquired organisms (p = 0.01). In the antimicrobial naïve cohort with late VAP 27 (71%) patients had community acquired organisms, whereas only 3 (16%) isolates in late VAP in those with prior therapy revealed community acquired flora (p 0.001).Conclusion: Patients who receive prior antimicrobial therapy have a significantly lower incidence of early VAP, but in those who developed either early or late VAP hospital acquired pathogens were more commonly isolated. Knowledge of prior antimicrobial exposure in a patient with early or late VAP will assist in determining the correct empiric antimicrobial choice.