title: A Comparative Evaluation of Different Diagnostic Modalities in the Diagnosis of Typhoid Fever Using a Composite Reference Standard: A Tertiary Hospital Based Study in Central India.
abstract: BACKGROUND
  Enteric fever, caused bySalmonella spp.is a major cause of morbidity and mortality worldwide and endemic in many developing countries including India and other South-East Asian countries. Blood culture is regarded as the gold standard for diagnosis. Currently, the standard serological method is tube agglutination with moderate sensitivity and specificity. Dot blot assay detecting IgM and IgG antibodies to a specific 50kD Outer Membrane Protein (OMP) antigen ofSalmonella spp. is a simple, reliable, affordable and rapid test which can help in the early diagnosis of typhoid fever.
  
  
  OBJECTIVE
  To systematically evaluate the different diagnostic modalities against a composite reference standard for the better diagnosis of typhoid fever in clinically suspected cases of typhoid fever.
  
  
  METHODS
  This cross-sectional, prospective analytical study was carried out at a tertiary care hospital attached to Medical College in central India from November 2011 to June 2013. A total of 163 blood samples, collected aseptically from patients clinically diagnosed of enteric fever, were tested using various component tests like blood culture, Tube Widal and Dot Enzyme Immuno Assay (Dot EIA) for IgG and/or IgM. Composite Reference Standard (CRS) was created for defining the confirmed cases of typhoid fever using the component tests, wherein culture positive and in absence of culture positivity any two component test positive patients were taken as confirmed cases. All the component tests were evaluated against the CRS for sensitivity, specificity, PPV and NPV and their significance in relation to the duration of illness using statistical tests of significance.
  
  
  RESULTS
  Blood culture was positive in 16 (9.81%) whereas, Tube Widal, IgM, IgG and IgM+IgG in combination were positive in 88(54%), 58(35.58%), 30 (18.40%) and 75 (46.01%) respectively. Using a two test criteria of CRS framed, a total of 104 patients were considered as confirmed cases. Though specificity of blood culture was 100%, the sensitivity was low with significant detection rate in 1stweek of illness. Tube Widal showed a sensitivity of 65.38% and specificity of 89.83% with significant detection rate in 2ndweek. Dot blot assay for IgM, IgG and Combined IgM and IgG showed a sensitivity of 71.15%, 65.28% and 51.72% respectively whereas, the specificity was 10.16%, 47.45% and 74.57% respectively with significant detection rate in 2ndand 3rdweek of illness.
  
  
  CONCLUSIONS
  It can be concluded that though blood culture is still the gold standard, Dot blot assay found to have high sensitivity and good specificity might be a practical alternative test for the rapid diagnosis of typhoid fever if interpreted with care particularly using a composite reference standard. Further, it is reliable, simple to perform and rapid; results being available in 1 hour when compared to 48 hours for blood culture and 18 hours for Tube Widal test.
authors.affiliation: Assistant Professor, Department of Microbiology, RKDF MCH and RC , Bhopal, India .
authors.forename: Veena
authors.initials: V
authors.lastname: Maheshwari
authors.affiliation: Associate Professor, Department of Microbiology, PCMS and RC , PCMS Campus, Bhopal, India .
authors.forename: Navinchandra Motiram
authors.initials: NM
authors.lastname: Kaore
authors.affiliation: Professor and Head, Department of Microbiology, L.N. Medical College , Bhopal, India .
authors.forename: Vijay Kumar
authors.initials: VK
authors.lastname: Ramnani
authors.affiliation: Student, DEHS , USA .
authors.forename: Sheil
authors.initials: S
authors.lastname: Sarda
keywords: Dot EIA; Salmonella enterica; Widal test