title: Accuracy of rapid strep testing in patients who have had recent streptococcal pharyngitis.
abstract: BACKGROUND
  Some clinicians have questioned the accuracy of rapid diagnosis of group A streptococcal pharyngitis by commercial immunochemical antigen test kits in the setting of recent streptococcal pharyngitis, believing that the false-positive rate was increased because of presumed antigen persistence.
  
  
  METHODS
  We studied 443 patients--211 cases--who had clinical pharyngitis diagnosed as group A beta-hemolytic streptococcus infection in the past 28 days and compared them with 232 control patients who had symptoms of pharyngitis but no recent diagnosis of streptococcal pharyngitis. Our aim was narrowly focused to compare the rapid strep test with the culture method we used in our clinical practice.
  
  
  RESULTS
  We found that the rapid strep test in this setting showed no difference in specificity (0.96 vs 0.98); hence, the assertion that rapid antigen testing had higher false-positive rates in those with recent infection was not confirmed. We also found that in patients who had recent streptococcal pharyngitis, the rapid strep test appears to be more reliable (0.91 vs 0.70, P < .001) than in those patients who had not had recent streptococcal pharyngitis.
  
  
  CONCLUSIONS
  The findings of this study indicate that the rapid strep test is both sensitive and specific in the setting of recent group A beta-hemolytic streptococcal pharyngitis, and its use might allow earlier treatment in this subgroup of patients.
authors.affiliation: Department of Family Medicine, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Sheeler
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Houston
authors.forename: Sharon
authors.initials: S
authors.lastname: Radke
authors.forename: Jane C
authors.initials: JC
authors.lastname: Dale
authors.forename: Steven C
authors.initials: SC
authors.lastname: Adamson
mesh_terms: D000942:Antigens, Bacterial / Q000032:analysis; D005189:False Positive Reactions; D006801:Humans; D010612:Pharyngitis / Q000175:diagnosis* / Q000382:microbiology; D011446:Prospective Studies; D011933:Reagent Kits, Diagnostic / Q000592:standards*; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013297:Streptococcus pyogenes / Q000276:immunology / Q000302:isolation & purification*; D014481:United States
chemical_list: D000942:Antigens, Bacterial; D011933:Reagent Kits, Diagnostic