Evaluation of Terminal Subcultures for Blood Cultures Monitored by VITAL System / 대한임상병리학회지

BACKGROUND: Many non-invasive, continuous-monitoring blood culture systems have introduced technology that reduces the time and labor. There is a report that terminal subculture is necessary to decrease false negative. The purpose of this study is to evaluate the terminal subcultures for blood cultures monitored by VITAL system and to determine the clinical significance of positive blood cultures not detected by VITAL system. METHODS: From June to August 1996, a total of 3,988 blood culture bottles were processed by VITAL system and terminal subcultures were performed on consecutive 5 day blood culture. Any culture that was instrument positive but negative upon terminal subculture was considered to be false positive. Any culture that was instrument negative but positive upon terminal subculture was considered to be false negative. And false negative were categorized into minor and major errors. RESULTS: Two-hundred and nineteen (5.5%) out of 3,988 blood culture bottles were signaled as positive by VITAL system. Twenty-four bottles out of 219 were VITAL positive but negative upon terminal subcultures (false positive rate, 0.8%). And seven of the 3,988 terminal subcultures were false negative (0.2%). Four out of seven were major error and three were minor error. The isolates of major error bottles were Staphylococcus spp. and minor error bottles were Escherichia coli and Candida tropicalis. These isolates were clinically significant pathogens, but there were no changes on antimicrobial chemotherapy after reporting the positive blood culture reports. CONCLUSIONS: These results suggest that using VITAL system, terminal subculture of 5 day instrument-negative blood culture bottles is not necessary and the VITAL system provides for the rapid and convenient tool for detecting bacteremia.

Evaluation of VITAL Automated Blood Culture System / 대한임상병리학회지

BACKGROUND: An evaluation was performed to assess the performance of continuously monitoring VITAL automated blood culture system (bio-Merieux, Marcy-l'Etoile, France) and to investigate the value of performing final subcultures at the end of the protocol. METHODS: A retrospective study was conducted over a period of one year (October 1996 to September 1997) with 7,078 blood culture bottles sent to Microbiology Department of Korea Veterans Hospital. Not only VITAL positive bottles but also all the VITAL negative bottles were observed under a microscope after Gram staining and subcultured aerobically and anaerobically at the end of 5-day protocol. All isolates were identified by the conventional method and ATB system. RESULTS: Among total 7,078 bottles, 688 bottles (9.72%) were declared positive by the system, of which 68 (0.96%) proved to be false positive. The final blind subculture permitted the detection of 96 falsely negative bottles (1.38%). The average time to detection was 38h 08, and 20% of 444 samples having microorganisms were detected during the first 12 h, 45% during the first 24 h, 63% within 48 h, and 87% within 120 h. 58 samples (13%), which contained 20 cases of Gram positive cocci and 20 cases of yeasts- especially 65% of C. parapsilosis, were declared negative by the system but gave a positive subculture. Among the positive bottles, 86.3% were detected by the slope algorithm, 10.6% by the delta algorithm, and 3.1% by the threshold algorithm. CONCLUSIONS: I conclude that the VITAL system must be modified to improve the detection of staphylococci and yeasts and a more sensitive computer algorithm may be required so that the terminal subcultures will not be necessary. Each laboratory must decide the value of terminal blind subcultures on the basis of patient population and the microorganisms that are most frequently isolated in their institution.

Comparison of Vital Automated Blood Culture System and Mannual Blood Culture Method / 대한임상미생물학회지

BACKGROUND: Continuous monitoring blood culture systems (CMBCS) reduce the time and false negative rates of bacterial growth compared with the traditional manual blood culture systems which have been used in many hospitals yet. The purpose of this study is to evaluate the terminal subcultures monitored by Vital system compared with the manual system and to determine the guideline of terminal subcultures. METHODS: A retrospective study was conducted over a period of one year (from January to December 1995) with manual blood culture system and and sixteen months (from February 1996 to May 1997) with Vital system. All of the positive and negative blood bottles were done Gram staining and subcultured aerobically and anaerobically with 7-day terminal subculture protocol. All of the isolates were identified with API systems or ATB systems. RESULTS: Among 3,344 cases with the manual system, 305 cases (9.1%) were declared positive and 424 cases (8.8%) out of 4,822 cases with Vital system were positve. The terminal subcultures detected 48 cases (1.44%) in manual system and 9 cases (0.19%) in Vital system according to 7-day protocol. No statistical differences were observed in results among 5 day, 7 day and terminal subcultures. Those of false negative organisms were gram positive cocci (22 cases), Enterobacteriaceae (13 cases), non-fermenters (12 cases) and gram positive rod (1 case) with the manual system and gram positive cocci (4 cases), Entrobacteriaceae (1 case), non-fermenter (1 case) and yeasts (3 cases) with Vital system. CONCLUSIONS: These results suggest that terminal subculture of Vital systemnegative blood culture bottles is not necessary except S. aureus and fungus bacteremia on the basis of clinical situation.