title: An evaluation of a novel dual treponemal/nontreponemal point-of-care test for syphilis as a tool to distinguish active from past treated infection.
abstract: BACKGROUND
  Most syphilis point-of-care (POC) tests detect treponemal antibodies, which persist after successful treatment. Subsequent POC tests are positive, despite no active infection, and can lead to unnecessary treatment. We evaluated a new POC test, incorporating a nontreponemal component, to distinguish active from past infection.
  
  
  METHODS
  Sera stored at 2 Australian laboratories were tested with DPP Screen and Confirm Assay. Treponemal and nontreponemal test lines were compared to corresponding conventional treponemal and nontreponemal reference test results: immunoassays and rapid plasma reagin (RPR), respectively, with RPR quantification by endpoint titration. POC test outcome concordance with conventional test results was assessed according to serological and clinical categories.
  
  
  RESULTS
  Among 1005 serum samples tested, DPP treponemal line sensitivity was 89.8% (95% confidence interval [CI], 87.3%-91.9%) and specificity was 99.3% (95% CI, 97.0%-99.9%). DPP nontreponemal line sensitivity was 94.2% (95% CI, 91.8%-96.0%) and specificity was 62.2% (95% CI, 57.5%-66.6%). DPP test outcome (pair of test lines) was concordant with both reference test results for 94.3% of 404 high-titer infections, 90.1% of 121 low-titer infections, 27.5% of 211 past/treated infections, and 78.1% of 242 infections classified as not syphilis. Among 211 past/treated infections, 49.8% were incorrectly identified as active infection and a further 22.8% as not syphilis.
  
  
  CONCLUSIONS
  DPP test use would result in identification of >93% of active syphilis infections, whereas just over half of past infections would be diagnosed as past or not syphilis, avoiding unnecessary treatment compared with other POC tests. This may be at the expense of missing some active infections; thus, its potential benefits will depend on the prevalence of past vs active infection in a population.
authors: Kirby Institute, University of New South Wales, Sydney.
authors: Louise M
authors: LM
authors: Causer
authors: Kirby Institute, University of New South Wales, Sydney.
authors: John M
authors: JM
authors: Kaldor
authors: Kirby Institute, University of New South Wales, Sydney.
authors: Damian P
authors: DP
authors: Conway
authors: Victorian Infectious Diseases Reference Laboratory, Melbourne.
authors: David E
authors: DE
authors: Leslie
authors: Melbourne Sexual Health Centre, Carlton.
authors: Ian
authors: I
authors: Denham
authors: Victorian Infectious Diseases Reference Laboratory, Melbourne.
authors: Theo
authors: T
authors: Karapanagiotidis
authors: Burnet Institute, Melbourne.
authors: Claire
authors: C
authors: Ryan
authors: Kirby Institute, University of New South Wales, Sydney.
authors: Handan
authors: H
authors: Wand
authors: Burnet Institute, Melbourne.
authors: David A
authors: DA
authors: Anderson
authors: SEALS Laboratory, Prince of Wales Hospital, Randwick.
authors: Peter W
authors: PW
authors: Robertson
authors: Sydney Sexual Health Centre.
authors: Anna M
authors: AM
authors: McNulty
authors: Kirby Institute, University of New South Wales, Sydney.
authors: Basil
authors: B
authors: Donovan
authors: Central Clinical School, Monash University, Melbourne, Australia.
authors: Christopher K
authors: CK
authors: Fairley
authors: Kirby Institute, University of New South Wales, Sydney.
authors: Rebecca J
authors: RJ
authors: Guy
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000907:Antibodies, Bacterial / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D000067716:Point-of-Care Testing; D015995:Prevalence; D012680:Sensitivity and Specificity; D013587:Syphilis / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology; D013588:Syphilis Serodiagnosis / Q000379:methods*; D014210:Treponema pallidum / Q000276:immunology*; D055815:Young Adult
chemical_list: D000907:Antibodies, Bacterial
keywords: diagnosis; point-of-care test; syphilis