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Clin Infect Dis. 2014 Sep 1;59(5):643-50. doi: 10.1093/cid/ciu400. Epub 2014 May 27.

Reflexive culture in adolescents and adults with group a streptococcal pharyngitis.

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  • 1Department of Laboratory Medicine.
  • 2Department of Laboratory Medicine Department of Microbiology Department of Medicine, University of Washington, Seattle.



Guidelines currently provide conflicting recommendations regarding the diagnosis of group A streptococcal (GAS) pharyngitis in adults. Clinical guidelines state that negative rapid antigen detection tests (RADTs) do not require confirmation by a backup method in adults, whereas laboratory-based guidelines mandate confirmation of a negative RADT in patients of all ages. The objective of this study was to assess the utility of reflexive culture following a negative RADT in adolescents and adults with suspected GAS pharyngitis.


A retrospective analysis of 726 patients, aged ≥13 years, with negative RADTs and positive GAS throat cultures, was performed between 1 January 2000 and 31 December 2011 at 2 academic medical centers in Seattle, Washington. Complication rates, treatment, modified Centor score, and bacterial burden in patients with negative RADTs and positive GAS throat cultures were assessed.


Modified Centor scores ≥2 were observed in 55% of patients with a negative RADT and positive GAS culture. Of these, 77% of patients had a moderate or heavy bacterial burden (≥2+). RADTs failed to detect some patients who presented with serious complications of GAS pharyngitis: 29 (4.0%) had peritonsillar abscesses and 2 (0.28%) were diagnosed with acute rheumatic fever. Providers found culture results to be useful for initiating antibiotic therapy or confirming a clinical diagnosis. Antibiotic treatment was prescribed in 68.7% of patients, with culture-directed initiation of therapy documented in 43.5%.


Reflexive GAS culture is clinically useful when RADTs are negative. RADTs fail to detect a substantial number of adult patients with clinically significant pharyngitis who can benefit from treatment.

© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail:


group A streptococcus; pharyngitis; rapid antigen detection test; strep throat

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