Previous cultures are not clinically useful for guiding empiric antibiotics in suspected ventilator-associated pneumonia: Secondary analysis from a randomized trial☆

Abstract 

Purpose

To examine the predictive validity of prior cultures at predicting the microorganism isolated at the time of suspicion of ventilator-associated pneumonia (VAP).

Materials and Methods

We 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).

Results

Two 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]).

Conclusions

There 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.

Keywords: Previous cultures, Empiric antibiotics, Ventilator-associated pneumonia