title: In vitro comparison of four rapid antigen tests for group A streptococcus detection.
abstract: OBJECTIVE
  To examine the analytical sensitivity of four rapid antigen tests (RADT) for detection of group A streptococcus (GAS).
  
  
  METHODS
  The sensitivities of four RADT kits to detect clinical and reference strains of GAS at different dilutions were compared. Test results were read by two people, and differences in interpretation were settled by a third reader.
  
  
  RESULTS
  A total of 697 tests were performed. For all kits, detection increased with increasing colony counts of GAS. One kit [ulti med Products, Deutschland, GmbH (UM)] was found to have the highest sensitivity, although there was no significant difference between it and one other kit (Testpack Plus). All kits were only faintly positive or negative at low colony counts.
  
  
  CONCLUSIONS
  The sensitivity of RADT for detecting GAS is related to inoculum size and the faint appearance of a positive test at low colony counts contributes to inter-observer variability. Sore throats with low colony counts have been shown to be clinically relevant.
authors.affiliation: Microbiology, Labtests, 37-41 Carbine Road, Mt Wellington, Auckland 1060, New Zealand. arlo.upton@labtests.co.nz.
authors.forename: Arlo
authors.initials: A
authors.lastname: Upton
authors.forename: Cathy
authors.initials: C
authors.lastname: Lowe
authors.forename: Joanna
authors.initials: J
authors.lastname: Stewart
authors.forename: Susan
authors.initials: S
authors.lastname: Taylor
authors.forename: Diana
authors.initials: D
authors.lastname: Lennon
mesh_terms: D000942:Antigens, Bacterial / Q000302:isolation & purification*; D006801:Humans; D008828:Microbiological Techniques; D010612:Pharyngitis / Q000382:microbiology; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis*; D013297:Streptococcus pyogenes / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D000942:Antigens, Bacterial