The Predictive Value of Preliminary Bacterial Colony Counts from Bronchoalveolar Lavage in Critically Ill Trauma Patients

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A common strategy for the diagnosis of ventilator-associated pneumonia (VAP) includes quantitative cultures from bronchoalveolar lavage (BAL). Often, empiric antibiotic therapy is initiated and continued until the final culture report. However, approximately 60 per cent of BAL cultures rule out VAP. Preliminary BAL results, obtained earlier, may identify these patients and allow early discontinuation of empiric antibiotics. This is desirable because unnecessary antibiotic therapy results in increased bacterial resistance, adverse drug events, and increased costs. The purpose of this study was to determine the value of preliminary BAL results for predicting final BAL results. A total of 1579 isolates from 868 BAL cultures over a 3-year period were analyzed. Preliminary and final colony counts for each isolate were categorized as either no growth (NG), insignificant (1-99,999 cfu/mL), or significant (> or = 100,000 cfu/mL). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of preliminary results were calculated based on individual isolates and individual BAL samples. The presence of concurrent antibiotic therapy was collected for all false-negative isolates. On preliminary report, there were 367 isolates with NG, 820 isolates with insignificant growth, and 392 isolates with significant growth. Overall preliminary culture results had a sensitivity of approximately 90 per cent and specificity of >90 per cent for the presence of VAP. Preliminary culture results accurately predicted the presence or absence of VAP in 838 (96.5%) of the BALs performed. Individual isolates and BAL samples with insignificant preliminary growth had greater reliability in predicting the absence of VAP than those with NG. There was no difference in the number of false-negative isolates that were taken while concurrent antibiotic therapy was present between insignificant and NG groups. Preliminary culture results yielding either insignificant or significant growth are highly predictive for final colony counts of similar magnitude. BALs with preliminary results demonstrating no growth are not as reliable. Isolates with significant preliminary growth should be considered clinically important, and antibiotic therapy should be changed, if necessary, to target such organisms. Isolates with insignificant preliminary growth have a low rate of false negatives; therefore, empiric antibiotic therapy specific for such organisms could be discontinued before obtaining final results. Empiric antibiotics should be continued until the final results are available in those patients with NG BALs.