title: Nested polymerase chain reaction on blood clots for gene encoding 56 kDa antigen and serology for the diagnosis of scrub typhus.
abstract: OBJECTIVE
  Scrub typhus is a zoonotic illness endemic in the Asia-Pacific region. Early diagnosis and appropriate management contribute significantly to preventing adverse outcomes including mortality. Serology is widely used for diagnosing scrub typhus. Recent reports suggest that polymerase chain reaction (PCR) could be a rapid and reliable alternative. This study assessed the utility of these tests for scrub typhus diagnosis.
  
  
  METHODS
  Nested PCR to detect the 56 kDa antigen gene of O. tsutsugamushi was performed on blood clots from 87 individuals with clinically suspected scrub typhus. Weil-Felix test and scrub typhus IgM ELISA were performed on serum samples from the same patients. As a gold standard reference test was not available, latent class analysis (LCA) was used to assess the performance of the three tests.
  
  
  RESULTS
  The LCA analysis showed the sensitivity of Weil-Felix test, IgM ELISA and PCR to be 59%, 100% and 58% respectively. The specificity of ELISA was only 73%, whereas those of the Weil-Felix test and PCR were 94% and 100% respectively.
  
  
  CONCLUSIONS
  Nested PCR using blood clots while specific, lacked sensitivity as compared to IgM ELISA. In resource-poor settings Weil-Felix test still remains valuable despite its moderate sensitivity.
authors.affiliation: Department of Microbiology, Christian Medical College, Vellore, India. prakjaj@yahoo.com
authors.forename: J A J
authors.initials: JA
authors.lastname: Prakash
authors.forename: M L
authors.initials: ML
authors.lastname: Kavitha
authors.forename: E
authors.initials: E
authors.lastname: Mathai
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001431:Bacteriological Techniques / Q000379:methods*; D001769:Blood / Q000382:microbiology*; D001777:Blood Coagulation; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006801:Humans; D012285:Orientia tsutsugamushi / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012612:Scrub Typhus / Q000175:diagnosis*; D012680:Sensitivity and Specificity
chemical_list: D000942:Antigens, Bacterial