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Adherence to an established diagnostic threshold for ventilator-associated pneumonia contributes to low false-negative rates in trauma patients

BACKGROUND The diagnosis of ventilator-associated pneumonia (VAP) in our institution has followed an established diagnostic threshold (DT) of equal to or greater than 105 colony-forming units (CFU) per milliliter on bronchoalveolar lavage (BAL) based on our previous study (PS). Because mortality from VAP is related to treatment delay, some have advocated a lower DT. The purpose of the current study (CS) was to evaluate the impact of adherence to this DT for VAP on false-negative (FN) rates and mortality in trauma patients. METHODS Consecutive patients over 9 years with VAP (defined as ≥105 CFU/mL in the BAL effluent) subsequent to the PS were identified. Data regarding each BAL performed and the colony counts of each organism identified were recorded. An FN BAL result was defined as any patient who had less than 105 CFU/mL and developed VAP with the same organism up to 7 days after the previous culture. The CS was then compared with the PS. RESULTS Over 9 years, 1,679 patients underwent 3,202 BALs. Of these, 79% were male, 88% experienced blunt injury, mean age and Injury Severity Score (ISS) were 44 years and 31, respectively. Overall, there were 73 FN BAL results (2.3%) in the CS compared with 3% in the PS (p = 0.092). In those patients with 104 organisms, the FN rate was reduced (7.5% vs. 11%, p = 0.045), and mortality was unchanged (5.4% vs. 8.3%, p = 0.361) in the CS compared with the PS. The use of the threshold equal to or greater than 105 resulted in a cumulative reduction in antibiotic charges of $1.57 million. CONCLUSION Continued adherence to the diagnostic threshold of equal to or greater than 105 for quantitative BAL in trauma patients has maintained a low incidence of FN BALs and reduced patient charges without impacting mortality. The purported benefit of a lower threshold is not supported. In addition, the potential sequelae of increased resistant organisms, antibiotic-related complications, and costs associated with prolonged unnecessary antibiotic exposure are minimized. LEVEL OF EVIDENCE Prognostic study, level III.