title: Reflexive culture in adolescents and adults with group A streptococcal pharyngitis.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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%.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Laboratory Medicine.
authors.forename: Tanis C
authors.initials: TC
authors.lastname: Dingle
authors.affiliation: Department of Laboratory Medicine.
authors.forename: April N
authors.initials: AN
authors.lastname: Abbott
authors.affiliation: Department of Laboratory Medicine Department of Microbiology Department of Medicine, University of Washington, Seattle.
authors.forename: Ferric C
authors.initials: FC
authors.lastname: Fang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000942:Antigens, Bacterial / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000039:Peritonsillar Abscess / Q000175:diagnosis / Q000382:microbiology; D010612:Pharyngitis / Q000175:diagnosis* / Q000382:microbiology; D012189:Retrospective Studies; D012213:Rheumatic Fever / Q000175:diagnosis / Q000382:microbiology; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000276:immunology / Q000302:isolation & purification*; D014861:Washington
chemical_list: D000942:Antigens, Bacterial
keywords: group A streptococcus; pharyngitis; rapid antigen detection test; strep throat