Dec 3, 1992 - monitoring blood culture system thatuses internal, fluorescent-CO2 sensors. .... NR7A media have been described previously (2). Incubation ...
JOURNAL
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Vol. 31, No. 3
CLINICAL MICROBIOLOGY, Mar. 1993, p. 552-557
0095-1137/93/030552-06$02.00/0 Copyright © 1993, American Society for Microbiology
Multicenter Clinical Evaluation of a Continuous Monitoring Blood Culture System Using Fluorescent-Sensor Technology (BACTEC 9240) FREDERICK S. NOLTE,l12* JANIS M. WILLIAMS,' ROBERT C. JERRIS,2'3 JOSEPHINE A. MORELLO,4'5 CINDY D. LEITCH,4 SCOYT MATUSHEK,4 LYNNE D. SCHWABE,6 FRANCIS DORIGAN,7 AND FRANK E. KOCKA7'8 Clinical Microbiology Laboratory, Emory University Hospital, 1 and Department of Pathology and Laboratory Medicine, Emory University School of Medicine,2 Atlanta, Georgia 30322; Clinical Microbiology Laboratory, DeKalb Medical Center, Atlanta, Georgia 30033'; Clinical Microbiology Laboratories, University of Chicago Hospitals, 4 and Departments of Pathology, Medicine, and Molecular Genetics and Cell Biology, University of Chicago Medical Center, 5 Chicago, Illinois 60637; Clinical Microbiology Laboratory, Evanston Hospital, Evanston, Illinois, 602016; Clinical Microbiology Laboratory, Cook County Hospital, Chicago, Illinois 606127; and Department of Pathology, Microbiology and Immunology, Chicago Medical School, North Chicago, Illinois 600648 Received 17 August 1992/Accepted 3 December 1992 The BACTEC 9240 (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) is a new continuousmonitoring blood culture system that uses internal, fluorescent-CO2 sensors. In a multicenter clinical trial, organism yield and times to detection with the prototype BACTEC 9240 system were compared with those of the BACTEC NR 660 system. Equal volumes of blood were inoculated into the bottles included in the study blood culture sets (aerobic and anaerobic 9240 and NR6A and NR7A bottles). A total of 9,391 aerobic and 8,951 anaerobic bottle pairs were inoculated with 9,801 blood specimens. A total of 587 clinically significant positive blood cultures and 415 cases of sepsis were studied. The standard 9240 aerobic bottle detected significantly more Staphylococcus aureus (P < 0.05), coagulase-negative staphylococci (P < 0.01), and total microorganisms (P < 0.001) than the NR6A bottle. The standard 9240 anaerobic bottle detected significantly more coagulase-negative staphylococci (P < 0.001), members of the family Enterobacteriaceae (P < 0.01), and total microorganisms (P < 0.001) than the NR7A bottle. A total of 420 positive cultures were detected in both systems; for 284, the time to detection was equivalent with both systems (within 12 h); for 123, the 9240 system was faster; and for 13, the NR 660 system was faster (P < 0.001). The average times to detection for the 9240 and the NR 660 systems were 20.2 and 27.5 h, respectively. Ninety-nine cultures were positive only in the 9240 system, and 68 cultures were positive only in the NR 660 system (P < 0.02). The 9240 system also detected significantly more episodes of bacteremia (P < 0.001). The false-positive rates for the 9240 and NR 660 systems were 2.2 and 2.3%, respectively. The false-negative rates for the two systems after 5 days of incubation did not differ significantly. The contamination rates for the 9240 and NR 660 systems were 1.9 and 1.5%, respectively (P < 0.05). In conclusion, the prototype 9240 system detected more clinically significant positive blood cultures and did so sooner than the NR 660 system, with the additional advantages of full automation, continuous monitoring, and noninvasive sampling.
The BACTEC 9240 instrument accommodates up to 240 blood culture bottles and serves as an incubator, agitator, and detection system. Each bottle contains a fluorescentCO2 sensor, and the sensors are monitored on a continuous basis (every 10 min). Cultures are recognized as positive by computer algorithms for growth detection based on an increasing rate of change as well as sustained increase in CO2 production rather than by the use of growth index threshold or delta values. Finally, the BACTEC 9240 is completely automated once the bottles have been loaded. We report the results of a multicenter clinical trial of the prototype BACTEC 9240 system in which the new system was compared with the BACTEC NR 660 system. The trial was conducted in five hospital laboratories with bottles inoculated with 2 to 5 ml of blood obtained from adult patients with suspected sepsis. (This work was presented in part at the 92nd Annual Meeting of the American Society for Microbiology, 26-30 May 1992, New Orleans, La. [7].)
Rapid and reliable detection of microorganisms in the blood is among the most important functions of the clinical microbiology laboratory. Several different blood culture systems and approaches are available to laboratories, each with its own relative strengths and limitations. The semiautomated BACTEC radiometric and nonradiometric systems (Becton Dickinson Diagnostic Instrument Systems, Sparks, Md.) are used around the world and have done much to improve the yield, time to detection, and workflow for blood cultures. Recently, several new instruments have been designed to automatically and continuously monitor blood cultures (6, 11). One such system is the BACTEC 9240. Although the BACTEC 9240 is similar to the previous BACTEC systems in that it relies on CO2 production to detect positive cultures, it differs in several important ways. *
Corresponding author. 552
VOL. 31, 1993
CLINICAL EVALUATION OF THE BACTEC 9240
Broth
C02 Sensor Excitation Filter
nEm ission Filter
/
Photo Diode Detector
Light Emitting Diode
FIG. 1. Schematic drawing of BACTEC 9240 blood culture bottle and CO2 detector system.
MATERIALS AND METHODS BACTEC 9240 system overview. A CO2 sensor is bonded to the base of each blood culture bottle and overlaid with 40 ml of a supplemented soybean casein broth (Fig. 1). The sensor is impermeable to ions, medium components, and blood but is freely permeable to CO2. Carbon dioxide produced by microorganisms growing in the medium diffuses into the sensor and dissolves in the water present in the sensor matrix, generating hydrogen ions. Increases in hydrogen ion concentration (decreases in pH) increase the fluorescence output of the sensor, changing the signal transmitted to the optical and electronic components of the instrument. The computer generates growth curves based on plots of fluorescence units versus time, and the data are analyzed automatically according to growth detection algorithms. Positive cultures are identified immediately by an indicator light on the front of the instrument as well as by lights at each bottle station and displayed on the computer monitor. The instrument is an incubator, shaker, and fluorescence detector that will hold a total of 240 culture bottles. The bottles are arranged in six racks, each of which has 40 bottle stations. Each station contains a light-emitting diode and a photo diode detector with appropriate excitation and emission filters (Fig. 1). The racks are rocked and heated at 35 1PC. A test cycle of all racks is completed every 10 min. Blood collection. The skin of the patients was disinfected by accepted methods, and when between 8 and 20 ml of blood had been collected, equal volumes of blood were inoculated into one standard 9240 aerobic (6F), one standard 9240 anaerobic (7F), one NR6A aerobic, and one NR7A anaerobic bottle. When the volume of blood collected was
