Rapid automated diagnosis of bacteremia by impedance detection

Lysis and filtration of blood culture specimens were combined with impedance detection of bacterial growth to facilitate the diganosis of bacteria. A blood lysis filtration technique 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 A 30 ml sample of the blood broth mixture was withdrawn from the conventional aerobic blood culture bottle and processed in parallel.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.