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International Quality Assurance Study for Characterization of Streptococcus pyogenes

Shona Neal,^1* Bernard Beall,² Kim Ekelund,³ Birgitta Henriques-Normark,⁴ Aftab Jasir,⁵ Dwight Johnson,⁶ Edward Kaplan,⁶ Marguerite Lovgren,⁷ Ralf Rene Reinert,^8, Members of the Strep-EURO Study Group and International Streptococcus Reference Laboratories, and Androulla Efstratiou¹

Respiratory and Systemic Infection Laboratory, Health Protection Agency Centre for Infections, 61 Colindale Avenue, London NW9 5HT, United Kingdom,¹ Respiratory Diseases Branch, Centers for Disease Control, Atlanta, Georgia,² Department of Bacteriology, Mycology and Parasitology, Statens Serum Institute, Copenhagen, Denmark,³ Department of Bacteriology, Swedish Institute for Infectious Disease Control, Stockholm, Sweden,⁴ Department of Laboratory Medicine, Lund University, Lund, Sweden,⁵ Department of Pediatrics, University of Minnesota Medical School, Minneapolis, Minnesota,⁶ Provincial Laboratory of Public Health, University of Alberta Hospital, Edmonton, Alberta, Canada,⁷ and Institute for Medical Microbiology, University Clinic Aachen, Aachen, Germany⁸

Received 19 October 2006/ Returned for modification 1 January 2007/ Accepted 21 January 2007

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 nontypeable (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 the performance between centers yielded typeability rates from 65 to 100% and concordance values from 83 to 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.

Published ahead of print on 31 January 2007.

Contributing members of the Strep-EURO Study Group and International Streptococcus Reference Laboratories included H. Goossens (Belgium), G. Tyrrell (Canada), L. Strakova (Czech Republic), M. Staum Kaltoft (Denmark), J. Vuopio-Varkila (Finland), L. Mihaila-Amrouche (France), M. Van der Linden (Germany), L. Zachariadou and J. Papaparaskevas (Greece), L. Valinsky (Israel), R. Creti (Italy), W. Wannet (Netherlands), D. Martin (New Zealand), M. Straut (Romania), C. Schalén, B. Luca, and J. Darenberg (Sweden), A. Tanna (United Kingdom), and V. Sakota (United States).

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