title: Comparative performance of the probable case definitions of dengue by WHO (2009) and the WHO-SEAR expert group (2011).
abstract: BACKGROUND
  The primary objective of this study was to find the performance of the 2009 probable case definition of dengue and compare it with the definition given by the WHO-SEAR expert group in 2011.
  
  
  METHODS
  A cross-sectional study was conducted in Thiruvananthapuram district of Kerala, which is hyperendemic for dengue. A consecutive series of 851 participants defined by the selection criteria were recruited from the primary, secondary, and tertiary health care settings. Sensitivity, specificity, predictive values, and likelihood ratios of the clinical case definitions were calculated using reverse transcriptase-polymerized chain reaction (RT-PCR) as gold standard in case of fever less than or equal to 5 days and serology (IgM positivity) for fever >5 days. Diagnostic odds ratio (DOR) was also calculated as a single indicator of performance of the case definition.
  
  
  RESULTS
  The 2009 World Health Organization (WHO) case definition had a sensitivity of 76·4% (69·6-82·1) and negative predictive value of 87·5%. The 2011 WHO-SEAR expert group case definition had a higher sensitivity of 87·9% (82·2-91·9) but lower negative predictive value of 86·6%. The three independent criteria which were significantly associated with dengue were thrombocytopenia less than 150,000 (OR 2·80), leukopenia (OR 2·28), and absence of backache (OR 2·68). The performance of 2009 case definition was better (DOR 2·4) than the 2011 WHO-SEAR expert group case definition. This was further enhanced when thrombocytopenia was specified as platelet count less than 150,000 (DOR2·7). When 'no backahe' was added as an additional criteria, the performance of both definitions improved.
  
  
  CONCLUSIONS
  The 2009 WHO case definition has better discriminatory power than the 2011 WHO-SEAR expert group case definition. The performance of 2009 WHO case definition is enhanced by specifying thrombocytopenia as platelet count less than 150,000. The inclusion of 'no backache' further improves the discriminatory power. This may be more useful in primary care settings, to rule out dengue.
authors.forename: Zinia T
authors.initials: ZT
authors.lastname: Nujum
authors.forename: Achu
authors.initials: A
authors.lastname: Thomas
authors.forename: K
authors.initials: K
authors.lastname: Vijayakumar
authors.forename: Radhakrishnan R
authors.initials: RR
authors.lastname: Nair
authors.forename: M Radhakrishna
authors.initials: MR
authors.lastname: Pillai
authors.forename: P S
authors.initials: PS
authors.lastname: Indu
authors.forename: Syam
authors.initials: S
authors.lastname: Sundar
authors.forename: Soumya
authors.initials: S
authors.lastname: Gopakumar
authors.forename: Devi
authors.initials: D
authors.lastname: Mohan
authors.forename: T K
authors.initials: TK
authors.lastname: Sudheeshkumar
mesh_terms: D015331:Cohort Studies; D021821:Communicable Diseases, Emerging; D003430:Cross-Sectional Studies; D003715:Dengue / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control; D005260:Female; D005334:Fever / Q000175:diagnosis* / Q000453:epidemiology; D017408:Guidelines as Topic; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D016017:Odds Ratio; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D009626:Terminology as Topic; D013921:Thrombocytopenia / Q000175:diagnosis* / Q000453:epidemiology; D014944:World Health Organization
keywords: Case definition,; Dengue,; Diagnostic odds ratio; SEAR,; WHO,