Polymerase chain reaction for Streptococcus pyogenes used to evaluate an optical immunoassay for the detection of group A streptococci in children with pharyngitis.
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.
Kaltwasser
G
G
Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis, MO, USA.
Diego
J
J
Welby-Sellenriek
P L
PL
Ferrett
R
R
Caparon
M
M
Storch
G A
GA
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*
D000942:Antigens, Bacterial