Mixed flora: indication for therapy or early warning sign?

ABSTRACT

"Mixed flora" is a commonly returned result yielding not in either indication for therapy or identification of potential causative organisms. We sought to determine whether mixed flora (MF) was in fact a harbinger of impending pneumonia or a benign result that could be therapeutically ignored. Bronchoalveolar lavage (BAL) results of injured adults undergoing mechanical ventilation in a trauma intensive care unit were stratified by identified organisms and by colony counts. The incidence of mixed flora as a component of the specimen report was compared for diagnostic (greater than 10(5) colony forming units/mL) versus nondiagnostic results using chi2 accepting P < 0.05 as significant. Nondiagnostic specimens were then stratified as MF only or MF and other identified pathogenic organisms. This group was further evaluated to determine the use of antibiotic therapy and development of pneumonia. Finally, patients with nondiagnostic reports and subsequent BAL were analyzed to determine specific species if subsequent BAL were required or if later pneumonia occurred. During 2007, 159 BALs were performed on injured patients of which 93 were diagnostic for pneumonia, whereas 66 were nondiagnostic. Of the diagnostic specimens, 15 (16%) included mixed flora. Of the 66 nondiagnostic specimens, 39 (59%) contained mixed flora. Nine (60%) of the 15 with diagnostic mixed flora were started on antibiotic therapy for an average of 6.2 days. The remaining 39 (82%) patients with mixed flora received no antibiotic therapy and never developed pneumonia. These data demonstrate that in the absence of diagnostic threshold of an identifiable pathogenic organism, therapy for pneumonia should not be instituted or continued.