title: Prevalence of Salmonella typhi among patients with febrile illness in rural and peri-urban populations of Vellore district, as determined by nested PCR targeting the flagellin gene.
abstract: OBJECTIVE
  Fever is one of the most common illnesses in all age groups in India. Typhoid fever is a continuing problem in developing countries such as India, which has poor sanitation facilities. The diagnosis of typhoid fever is still made by conventional culture-based isolation and identification. Serologic diagnostic tests, though widely used, have many deficiencies. Our objective was to investigate a molecular nested polymerase chain reaction (nPCR) technique to detect Salmonella typhi among patients with febrile illness in rural and peri-urban communities in Vellore district (Tamil Nadu, India).
  
  
  METHODS
  nPCR targeting the flagellin gene (fliC) was carried out using HotStar Taq DNA polymerase on DNA extracted from the buffy coat fraction of blood samples. Blood culture was done in a completely automated blood culture system, BacT/Alert(R), on prospectively collected blood samples. Relevant clinicopathologic data were obtained.
  
  
  RESULTS
  nPCR was found to have a lower limit of detection of 0.01 colony-forming units per milliliter. The prevalence of typhoid fever as estimated by nPCR was 4.7% in pyrexia of unknown origin (PUO) in the rural/peri-urban communities of Vellore district. The prevalence of S. typhi as estimated by blood culture was 2.0%, which was lower than the nPCR estimation. nPCR had sensitivity and specificity of 100% and 97.3%, respectively. The observed agreement between blood culture and nPCR was 0.973 and the Kappa coefficient was 0.59 (p < 0.0001). The frequency of typhoid fever as detected by nPCR was 4.35% among rural patients and 5.32% among peri-urban individuals.
  
  
  CONCLUSIONS
  nPCR on DNA extracts of buffy-coat samples using HotStar Taq was found to be a valuable and specific technique for diagnosis of typhoid fever.
authors.affiliation: Sri Narayani Hospital & Research Centre, Vellore, Tamil Nadu, India. director@snhrc.org
authors.forename: Balaji
authors.initials: B
authors.lastname: Nandagopal
authors.forename: Sathish
authors.initials: S
authors.lastname: Sankar
authors.forename: Karthikeyan
authors.initials: K
authors.lastname: Lingesan
authors.forename: Kumarasekharan Chandrasekharan
authors.initials: KC
authors.lastname: Appu
authors.forename: Baby
authors.initials: B
authors.lastname: Padmini
authors.forename: Gopalan
authors.initials: G
authors.lastname: Sridharan
authors.forename: Anil Kumar
authors.initials: AK
authors.lastname: Gopinath
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D005408:Flagellin / Q000235:genetics*; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction / Q000379:methods*; D015995:Prevalence; D012424:Rural Population; D012485:Salmonella typhi / Q000235:genetics* / Q000302:isolation & purification; D014435:Typhoid Fever / Q000453:epidemiology* / Q000382:microbiology*; D014505:Urban Population; D055815:Young Adult
chemical_list: D005408:Flagellin