Accuracy and reproducibility of the IDS RapID STR system for species identification of streptococci

Abstract

The RapID STR system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) was evaluated in the identification of 266 streptococci. Organisms included 60 beta-hemolytic streptococci, 71 group D strains (48 enterococci and 23 nonenterococci), 26 Streptococcus pneumoniae, and 109 viridans group strains. With concomitant optochin testing, as is currently recommended by the manufacturer for all alpha-hemolytic strains, the RapID STR system correctly identified 100% of beta-hemolytic strains, 87.3% of group D strains (93.7% of enterococci, 73.9% of nonenterococci), 88.5% of S. pneumoniae, and 72.5% of viridans strains. Without the use of optochin, the correct identification of S. pneumoniae and the viridans group was 26.9 and 52.3%, respectively. The RapID STR system incorrectly identified 3.0% of strains, including four group D streptococci, three pneumococci, and one viridans isolate. Reproducibility was excellent, with 95% of strains tested in triplicate yielding identical results on each of the three occasions. The RapID STR system represents a worthwhile advance in streptococcal species identification, especially for group D and viridans strains.