title: Diagnostic accuracy of a loop-mediated isothermal PCR assay for detection of Orientia tsutsugamushi during acute Scrub Typhus infection.
abstract: BACKGROUND
  There is an urgent need to develop rapid and accurate point-of-care (POC) technologies for acute scrub typhus diagnosis in low-resource, primary health care settings to guide clinical therapy.
  
  
  RESULTS
  In this study we present the clinical evaluation of loop-mediated isothermal PCR assay (LAMP) in the context of a prospective fever study, including 161 patients from scrub typhus-endemic Chiang Rai, northern Thailand. A robust reference comparator set comprising following 'scrub typhus infection criteria' (STIC) was used: a) positive cell culture isolate and/or b) an admission IgM titer ≥1∶12,800 using the 'gold standard' indirect immunofluorescence assay (IFA) and/or c) a 4-fold rising IFA IgM titer and/or d) a positive result in at least two out of three PCR assays. Compared to the STIC criteria, all PCR assays (including LAMP) demonstrated high specificity ranging from 96-99%, with sensitivities varying from 40% to 56%, similar to the antibody based rapid test, which had a sensitivity of 47% and a specificity of 95%.
  
  
  CONCLUSIONS
  The diagnostic accuracy of the LAMP assay was similar to realtime and nested conventional PCR assays, but superior to the antibody-based rapid test in the early disease course. The combination of DNA- and antibody-based detection methods increased sensitivity with minimal reduction of specificity, and expanded the timeframe of adequate diagnostic coverage throughout the acute phase of scrub typhus.
authors.affiliation: Mahidol-Oxford Tropical Medicine Programme, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Paris
authors.forename: Stuart D
authors.initials: SD
authors.lastname: Blacksell
authors.forename: Pruksa
authors.initials: P
authors.lastname: Nawtaisong
authors.forename: Kemajittra
authors.initials: K
authors.lastname: Jenjaroen
authors.forename: Achara
authors.initials: A
authors.lastname: Teeraratkul
authors.forename: Wirongrong
authors.initials: W
authors.lastname: Chierakul
authors.forename: Vanaporn
authors.initials: V
authors.lastname: Wuthiekanun
authors.forename: Pacharee
authors.initials: P
authors.lastname: Kantipong
authors.forename: Nicholas P J
authors.initials: NP
authors.lastname: Day
mesh_terms: D000208:Acute Disease; D000328:Adult; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D002522:Chlorocebus aethiops; D004269:DNA, Bacterial / Q000097:blood / Q000737:chemistry; D005260:Female; D005334:Fever / Q000382:microbiology; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008875:Middle Aged; D012285:Orientia tsutsugamushi / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D012612:Scrub Typhus / Q000175:diagnosis / Q000382:microbiology*; D013785:Thailand; D014709:Vero Cells
chemical_list: D000907:Antibodies, Bacterial; D004269:DNA, Bacterial; D007075:Immunoglobulin M