title: Etiologic predictive value of a rapid immunoassay for the detection of group A Streptococcus antigen from throat swabs in patients presenting with a sore throat.
abstract: BACKGROUND
  Clinical reasoning utilizing certain symptoms and scores has not proven to be a reliable decision-making tool to determine whether or not to suspect a group A Streptococcus (GAS) infection in the patient presenting with a sore throat. Culture as the so-called 'gold standard' is impracticable because it takes 1 to 2 days (and even longer in remote locations) for a result, and thus treatment decisions will be made without the result available. Rapid diagnostic antigen tests have demonstrated sufficient sensitivities and specificities in detecting GAS antigens to identify GAS throat infections.
  
  
  METHODS
  Throat swab samples were collected from patients attending the Mount Isa Hospital emergency department for a sore throat; these samples were compared to swab samples collected from healthy controls who did not have a sore throat. Both groups were aged 3-15 years. All swab samples were analyzed with a point-of-care test (Alere Test Pack +Plus with OBC Strep A). The etiologic predictive value (EPV) of the throat swab was calculated.
  
  
  RESULTS
  The 95% confidence interval for positive EPV was 88-100% and for negative EPV was 97-99%, depending on assumptions made.
  
  
  CONCLUSIONS
  This study demonstrates that the point-of-care test Alere Test Pack +Plus Strep A has a high positive predictive value and is able to rule in GAS infection as long as the proportion of carriers is low. Also the negative predictive value for ruling out GAS as the etiologic agent is very high irrespective of the carrier rate. Hence, this test is always useful to rule out GAS infection.
authors.affiliation: North West Hospital and Health Service, Mount Isa, QLD, Australia; James Cook University, Townsville, QLD, Australia: Mount Isa Centre for Rural and Remote Health, Mount Isa, QLD, Australia; Mount Isa Hospital Emergency Department, Mount Isa, QLD, Australia. Electronic address: ulrich.orda@gmail.com.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Orda
authors.affiliation: Cairns Clinical School, Cairns, QLD, Australia; James Cook University, Townsville, QLD, Australia; Research and Development Unit for Primary Health Care and Dental Care, Southern Älvsborg County, Region Västra Götaland, Sweden; Department of Public Health and Community Medicine, Institute of Medicine, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Ronny
authors.initials: R
authors.lastname: Gunnarsson
authors.affiliation: North West Hospital and Health Service, Mount Isa, QLD, Australia; James Cook University, Townsville, QLD, Australia: Mount Isa Centre for Rural and Remote Health, Mount Isa, QLD, Australia.
authors.forename: Sabine
authors.initials: S
authors.lastname: Orda
authors.affiliation: National Trauma Research Institute, Melbourne, VIC, Australia; Department of Surgery, Monash University, Melbourne, VIC, Australia; Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, VIC, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Fitzgerald
authors.affiliation: Mount Isa Hospital Emergency Department, Mount Isa, QLD, Australia.
authors.forename: Geoff
authors.initials: G
authors.lastname: Rofe
authors.affiliation: James Cook University, Townsville, QLD, Australia: Mount Isa Centre for Rural and Remote Health, Mount Isa, QLD, Australia; Mount Isa Hospital Emergency Department, Mount Isa, QLD, Australia.
authors.forename: Anna
authors.initials: A
authors.lastname: Dargan
mesh_terms: D000293:Adolescent; D000942:Antigens, Bacterial / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007118:Immunoassay; D010612:Pharyngitis / Q000175:diagnosis* / Q000209:etiology; D010614:Pharynx / Q000382:microbiology*; D011237:Predictive Value of Tests; D013290:Streptococcal Infections / Q000175:diagnosis; D013297:Streptococcus pyogenes / Q000302:isolation & purification*
chemical_list: D000942:Antigens, Bacterial
keywords: Antibiotic prescribing; Clinical reasoning; Etiologic predictive value; Group A Streptococci; Pharyngitis; Rapid Antigen Detection Test