Evaluation of nested PCR and loop mediated isothermal amplification assay (LAMP) targeting 47 kDa gene of Orientia tsutsugamushi for diagnosis of scrub typhus.Indian J Med Microbiol. 2021 Oct-Dec; 39(4):475-478.IJ
Diagnostic testing, in particular early detection, is critical for scrub typhus, as most infected individuals have nonspecific symptoms that are easily confused with dengue and malaria. PCR and LAMP offer an alternative DNA amplification method for detection of Orientia tsutsugamushi. Detection of Orientia tsutsugamushi DNA by targeting the 47-kDa gene using nested PCR and LAMP for diagnosis of scrub typhus.
A cross-sectional study in a tertiary care hospital in central India. The present study was done on a total of 274 patients with fever of five days or more and negative for other causes of fever viz. malaria, dengue and enteric fever. From each patient 5 ml of blood samples was collected in EDTA vial for molecular tests (PCR and LAMP) and in plain vial for serological tests (IgM IFA). The data was entered in Excel sheet and 2 × 2 tables were created to find sensitivity, specificity, positive and negative likelihood ratios, disease prevalence, positive and negative predictive values and accuracy.
PCR showed a sensitivity of 29.73% while the sensitivity of LAMP was 16.22%. The specificity of nested PCR and LAMP was very high, 99.58% and 99.16% respectively. The diagnostic accuracy of nested PCR (90.15%) was found to be marginally better than LAMP (87.96%).
For the treatment of scrub typhus, a gene-based diagnostic test would enable earlier and more accurate detection of the causative agents of the disease than serology in admission samples of patients with acute febrile illness in endemic areas.