• Kevin M Sanders, Neill K J Adhikari, Jan O Friedrich, Andrew Day, Xuran Jiang, Daren Heyland, and Canadian Critical Care Trials Group.
• Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada M5T 2S8.
• J Crit Care. 2008 Mar 1;23(1):58-63.

PurposeTo examine the predictive validity of prior cultures at predicting the microorganism isolated at the time of suspicion of ventilator-associated pneumonia (VAP).Materials And MethodsWe performed a retrospective analysis of a randomized controlled trial of different diagnostic and antibiotic strategies. In a subset of patients with pre-enrollment cultures, we examined agreement between cultures 1 to 3 days before suspicion of VAP and enrollment cultures performed on the day of suspicion of VAP and potential antibiotic error rates (estimated using the equation 1 - crude agreement).ResultsTwo hundred eighty-one (39%) of 739 patients had pre-enrollment culture. One hundred thirty (46%) of 281 yielded a pathogenic microorganism. In patients with positive pre-enrollment cultures, crude agreement was 0.63 (95% confidence interval, 0.55-0.71) for organism, 0.84 (0.77-0.89) for Gram class, and 0.61 (0.52-0.69) for species with sensitivity. Potential antibiotic error rates ranged from 16% (11%-33%) to 39% (31%-48%). Better agreement (P = .033) occurred in isolates from patients receiving new antibiotics during the surveillance period (0.78 [0.64-0.87]) compared to those not on antibiotics (0.58 [0.45-0.69]), or on no new antibiotics (0.50 [0.32-0.68]).ConclusionsThere is poor agreement between prior cultures and cultures performed at time of suspicion of VAP. Prior cultures should not be used to narrow the spectrum of empiric antibiotics.

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