title: The tale of two serologic tests to screen for syphilis--treponemal and nontreponemal: does the order matter?
abstract: BACKGROUND
  Standard syphilis screening involves an initial screening with a nontreponemal test and confirmation of positives with a treponemal test. However, some laboratories have reversed the order. There is no detailed quantitative and qualitative evaluation for the order of testing. In this study, we analyzed the health and economic outcomes of the order of testing for the 2 serologic tests used in syphilis screening under pure screening settings.
  
  
  METHODS
  We used a cohort decision analysis to examine the health and economic outcomes of the screening algorithms for low and high prevalence settings. The 2-step algorithms were nontreponemal followed by treponemal (Nontrep-First) and treponemal followed by nontreponemal (Trep-First). We included the 1-step algorithms (treponemal only [Trep-Only] and an on-site nontreponemal only [Nontrep-Only]) for comparison. We estimated overtreatment rates and the number of confirmatory tests required for each algorithm.
  
  
  RESULTS
  For a cohort of 10,000 individuals, our results indicated that the overtreatment rates were substantially higher (more than 3 times) for the 1-step algorithms, although they treated a higher number of cases (over 15%). The 2-step algorithms detected and treated the same number of individuals. Among the 2-step algorithms, the Nontrep-First was more cost-effective in the low prevalence setting ($1400 vs. $1500 per adverse outcome prevented) and more cost-saving ($102,000 vs. $84,000) in the high prevalence setting.
  
  
  CONCLUSIONS
  The difference in cost was largely due to the substantially higher number of confirmatory tests required for the Trep-First algorithm, although the number of cases detected and treated was the same.
authors.affiliation: Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. kowusuedusei@cdc.gov
authors.forename: Kwame
authors.initials: K
authors.lastname: Owusu-Edusei
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Koski
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Ballard
mesh_terms: D000465:Algorithms; D003362:Cost-Benefit Analysis; D006801:Humans; D008403:Mass Screening / Q000379:methods; D010949:Plasma / Q000276:immunology; D015995:Prevalence; D011935:Reagins / Q000097:blood; D012680:Sensitivity and Specificity; D013587:Syphilis / Q000175:diagnosis* / Q000191:economics / Q000453:epidemiology; D013588:Syphilis Serodiagnosis / Q000191:economics / Q000379:methods*; D014210:Treponema pallidum / Q000276:immunology*
chemical_list: D011935:Reagins