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

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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.

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