Evaluation of Terminal Subcultures for Blood Cultures Monitored by VITAL System

Lee, Jung Soo; Lee, Mi Ae; Chung, Wha Soon

Abstract

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.