Repeat subculture of known positive blood cultures: costly and ineffective in detecting polymicrobial bacteremias.

Reincubation and subsequent subculture at 72 h of previously positive blood cultures failed to demonstrate an increase in detection of polymicrobial bacteremia as has been previously reported. These procedures increased the cost of blood cultures between 140-192% without yielding new organisms. No new information was gained in 94.7% of cultures and, in 11.1% of the cultures, less information was obtained either because the cultures were sterile or because the original organisms could not be reisolated.