Evaluation of the Performance of Various Diagnostic Modalities Available for the Detection of Scrub Typhus in Acute Undifferentiated Febrile Illness (AUFI) Cases at a Teaching Hospital in North Chhattisgarh, India.

Introduction: Due to the lack of adequate data on the effectiveness of diagnostic methods and the ambiguous clinical symptoms that overlap with other febrile illnesses, diagnosing scrub typhus is difficult. This study aims to compare the accuracy of various investigations required for the diagnosis of scrub typhus like immunoglobulin G/immunoglobulin M (IgG/IgM) rapid test, IgM enzyme-linked immunosorbent assay (ELISA), and real-time polymerase chain reaction (RT-PCR) from a patient's serum.

Methods: This is a prospective study that includes all clinically suspected patients who visited the Outpatient Department (OPD) of Medicine and were admitted to the Medicine wards and Intensive Care Units of Rajmata Shrimati Devendra Kumari Singhdeo Government Medical College, Ambikapur, Chhattisgarh, India. The patients' samples were tested initially using the IgG/IgM rapid test, further confirmed by ELISA, and then subjected to RT-PCR for final confirmation.

Results: A total of 1,620 cases of acute undifferentiated febrile illness were tested, of which 82 tested positive for scrub typhus IgM rapid test. These 82 cases were further tested for confirmation using IgM ELISA, which showed 110 positive results. Additionally, RT-PCR was applied to all 1,620 samples using the DIAGsure Tropical Fever Panel Kit (3B BlackBio Dx Limited, Bhopal, India), resulting in 98 samples testing positive for scrub typhus. Both the ELISA and the rapid diagnostic test offer high capacity for discrimination, with sensitivity and specificity of 92.40%, 93.18%, and 99.20%, 98.17%, respectively (10.9% of cases came positive in serology which was negative in RT-PCR). It can be due to its nonspecific binding with antibodies of other febrile illnesses such as malaria, enteric fever, pulmonary tuberculosis, leptospirosis, etc. Conclusion: RT-PCR has shown excellent results with a sensitivity of >95% and specificity of >99%. Given its high sensitivity and specificity, along with clinical findings, RT-PCR is highly effective in detecting scrub typhus, especially for diagnosing early stages of the disease in cases of acute febrile illness with a duration of less than seven days. In reference labs, RT-PCR is the primary method for confirmation. This paper offers a thorough assessment of all the diagnostic tests for scrub typhus that are now accessible in a setting with limited resources, such as our north Chhattisgarh region.