title: Polymerase chain reaction for Streptococcus pyogenes used to evaluate an optical immunoassay for the detection of group A streptococci in children with pharyngitis.
abstract: BACKGROUND
  In evaluations of sensitive rapid tests for group A streptococci such as the optical immunoassay (OIA), some samples are positive by the antigen test but negative by culture. A method is needed for resolving these discrepant results.
  
  
  OBJECTIVE
  To develop a PCR-based assay to detect group A streptococci and to use it to establish a reference standard for evaluating an OIA for group A streptococcal antigen.
  
  
  METHODS
  A PCR assay that detects a segment of the MF gene of Streptococcus pyogenes was developed for the detection of group A streptococci in throat swabs. Paired swabs were obtained from 200 children with symptomatic pharyngitis and used to perform OIA, agar culture, broth-enhanced culture and PCR. As a reference standard any patient with group A streptococci detected by either culture or PCR was considered to be truly positive.
  
  
  RESULTS
  In comparison to agar and broth-enhanced culture procedures, OIA had sensitivities of 82 and 80% and specificities of 87 and 89%, respectively. Eight (44%) of 18 samples that were positive by OIA but negative by culture were positive for group A streptococci by PCR. Compared with the reference standard, sensitivities were OIA 76%, agar culture 79%, broth-enhanced culture 86% and PCR 96%. The specificity of OIA was 92%.
  
  
  CONCLUSIONS
  PCR can be used to establish a reference standard for evaluating rapid tests for group A streptococci. With this reference standard OIA was nearly as sensitive as but less specific than agar culture for detection of group A streptococci. Maximum detection requires use of both tests.
authors.affiliation: Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: G
authors.initials: G
authors.lastname: Kaltwasser
authors.forename: J
authors.initials: J
authors.lastname: Diego
authors.forename: P L
authors.initials: PL
authors.lastname: Welby-Sellenriek
authors.forename: R
authors.initials: R
authors.lastname: Ferrett
authors.forename: M
authors.initials: M
authors.lastname: Caparon
authors.forename: G A
authors.initials: GA
authors.lastname: Storch
mesh_terms: D000942:Antigens, Bacterial / Q000032:analysis; D002648:Child; D006801:Humans; D007118:Immunoassay; D010612:Pharyngitis / Q000175:diagnosis*; D016133:Polymerase Chain Reaction; D013290:Streptococcal Infections / Q000175:diagnosis*; D013297:Streptococcus pyogenes / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D000942:Antigens, Bacterial