Rapid automated disgnosis of bacteremia by impedance detection

Lysis and filtration of blood culture specimens were combined with impedance detection of bacterial growth to facilitate the diagnosis of bacteremia. A blood lysis-filtration technique (Zierdt et al., 1976) was coupled to a simple, inexpensive automated detection system. The practical and technical aspects of the impedance detection system are discussed. This new blood culturing system was compared to a conventional system for 264 aerobic blood cultures. A 30-ml sample of the blood-broth mixture was withdrawn from the conventional aerobic blood culture bottle and processed in parallel. Excluding the isolation of the commonly recognized contaminants, the detection efficiency was 36% greater in the new system. A total of 53 blood cultures from 107 patients were positive by one or both methods. The new system detected 92% of the total number of positive cultures, compared with 56% detected by the routine method. The explanation of the differences is discussed.