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J. Clin. Microbiol. doi:10.1128/JCM.02146-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

International quality assurance study for the characterization of Streptococcus pyogenes

^* To whom correspondence should be addressed. Email: shona.neal{at}hpa.org.uk.

	Abstract

Surveillance of group A streptococcal (GAS) infections was undertaken as a major component of the European Commission-funded project on severe GAS disease in Europe (strep-EURO). One aim of strep-EURO was to improve the quality of GAS characterization by standardization of methods. An external quality assurance study (EQA) was therefore carried out to evaluate current global performance.

Eleven strep-EURO and seven other streptococcal reference centers received a panel of 20 coded GAS isolates for typing. Conventional phenotypic typing (based on cell-surface T and M protein antigens and opacity factor (OF) production) and molecular methods (emm gene typing) were used either as single or combined approaches to GAS typing. T typing was performed by 16 centers; 12 centers found one or more of the 20 strains non-typeable (typeability, 89%), and 11 centers reported at least one incorrect result (concordance, 93%). The 10 centers that tested for OF production achieved 96% concordance. Limited availability of antisera resulted in poor typeability values from the four centers that performed phenotypic M typing (41%), three of which also performed anti-OF typing (typeability 63%); however, concordance was high for both M (100%) and anti-OF (94%) typing. In contrast, the 15 centers that performed emm gene sequencing achieved excellent typeability (97%) and concordance (98%), although comparison of performance between centers yielded typeability rates from 65-100% and concordance from 83-100%.

With the rapid expansion and use of molecular genotypic methods to characterize GAS, continuation of EQA is essential in order to achieve international standardization and comparison of type distributions.

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