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Войти в исследования Indian journal of medical microbiology · 2026
Determining an Optical Density (OD) cut-off value of IgM Enzyme-Linked Immunosorbent Assay (ELISA) for the diagnosis of Scrub typhus in the selected states of Northeast India.
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Yumlembam Bishwabati, Devi Khuraijam Ranjana, Bidyarani K, Bidyalakshmi Y, Manojkumar R K, Majumdar Tapan, Christina Soubam
Аннотация
PURPOSE: Scrub typhus, an acute febrile illness caused by the obligate intracellular bacterium Orientia tsutsugamushi, is increasingly reported across Northeast India. IgM enzyme-linked immunosorbent assay (ELISA) remains the most commonly used and cost-effective serological test for diagnosis. However, the performance of IgM ELISA is highly dependent on region-specific optical density (OD) cut-off values to minimise both over-diagnosis due to background seropositivity and missed cases in endemic areas. The present study was undertaken to establish an appropriate OD cut-off for Scrub typhus IgM ELISA in Northeast India using Receiver Operating Characteristic (ROC) curve analysis.
METHODS: This multicentric study, conducted across centers in Manipur and Tripura, collected 300 serum samples over two years (2021-2022). The samples comprised three equal groups of 100 each: healthy volunteers with no recent febrile illness, patients with unrelated febrile illnesses (clinically suspected enteric fever or dengue), and scrub typhus cases. All samples were tested using the Scrub Typhus Detect™ ELISA kit (InBios), and the resulting optical density values were analyzed by ROC curve to determine the optimal diagnostic cut-off.
RESULTS: ROC curve analysis identified two potential OD cut-off values (0.331 and 0.562). The higher cut-off demonstrated improved diagnostic performance, with an area under the ROC curve (AUC) of 0.992, indicating excellent discriminatory ability.
CONCLUSIONS: An OD cut-off value of 0.562 was identified for the InBios Scrub Typhus Detect™ IgM ELISA using a clinical reference standard in samples from Manipur and Tripura in Northeast India. Although the proposed cut-off demonstrated good diagnostic performance, the findings should be interpreted in light of the study limitations. Prospective multicentric validation using independent reference standards is required.
METHODS: This multicentric study, conducted across centers in Manipur and Tripura, collected 300 serum samples over two years (2021-2022). The samples comprised three equal groups of 100 each: healthy volunteers with no recent febrile illness, patients with unrelated febrile illnesses (clinically suspected enteric fever or dengue), and scrub typhus cases. All samples were tested using the Scrub Typhus Detect™ ELISA kit (InBios), and the resulting optical density values were analyzed by ROC curve to determine the optimal diagnostic cut-off.
RESULTS: ROC curve analysis identified two potential OD cut-off values (0.331 and 0.562). The higher cut-off demonstrated improved diagnostic performance, with an area under the ROC curve (AUC) of 0.992, indicating excellent discriminatory ability.
CONCLUSIONS: An OD cut-off value of 0.562 was identified for the InBios Scrub Typhus Detect™ IgM ELISA using a clinical reference standard in samples from Manipur and Tripura in Northeast India. Although the proposed cut-off demonstrated good diagnostic performance, the findings should be interpreted in light of the study limitations. Prospective multicentric validation using independent reference standards is required.