Comparative Evaluation of IgM Enzyme-Linked Immunosorbent Assay (ELISA) and Real-Time PCR for the Early Diagnosis of Scrub Typhus in Patients With Febrile Illness.

INTRODUCTION

Scrub typhus, caused by Orientia tsutsugamushi, is a major cause of acute undifferentiated febrile illness (AUFI) in India. Timely diagnosis is challenging due to the non-specific clinical presentation. While IgM enzyme-linked immunosorbent assay (ELISA) is widely used, molecular methods like real-time PCR (RT-PCR) offer the potential for early detection. This study compared the performance of IgM ELISA and RT-PCR in diagnosing scrub typhus in patients with febrile illness.

METHODS

A cross-sectional study was conducted from January to April 2024. Blood samples were collected from 156 patients with febrile illness of less than 14 days. All samples were tested for scrub typhus IgM ELISA. ELISA-positive samples and a random selection of ELISA-negative, clinically suspected samples were subjected to RT-PCR for confirmation.

RESULTS

Of the 156 patients, 46 (29.5%) were positive by IgM ELISA. Among these 46 ELISA-positive cases, 15 (32.6%) were positive by RT-PCR. A stark contrast was observed when analyzed by fever duration. Among the 15 RT-PCR positive cases, 100% had a fever duration of less than seven days. In contrast, only 17 (37.0%) of the 46 IgM ELISA-positive cases presented within the first seven days of fever (p<0.001). The 31 IgM ELISA-positive but RT-PCR-negative cases were predominantly from the later febrile phase (seven to 14 days).

CONCLUSIONS

RT-PCR is a superior tool for the early diagnosis of scrub typhus within the first week of fever, while IgM ELISA becomes more reliable thereafter. A diagnostic approach utilizing RT-PCR in the initial febrile phase and serology in the later phase can significantly improve the accuracy and timeliness of scrub typhus diagnosis.