Epidemiology, clinical characteristics, diagnosis, and complications of scrub typhus infection in Nepal: a systematic review

Molecular Assay Versus Serology for Diagnosis of Scrub Typhus Among Patients With Acute Febrile Illness: A Retrospective Study

BACKGROUND AND OBJECTIVES

The epidemiology of scrub typhus caused by Orientia tsutsugamushi has been growing in Odisha, India. The most common symptoms include fever, cough, lymphadenopathy, eschar, and rash. In India, enzyme-linked immunosorbent assays (ELISA) and DNA real-time polymerase chain reaction (DNA RT-PCR) are the most commonly used methods to diagnose scrub typhus. We conducted this study to determine the pattern of symptoms and association between the findings of ELISA and DNA RT-PCR.

METHODS

This retrospective study was accomplished at the Kalinga Institute of Medical Sciences (KIMS), Bhubaneswar, OR, IND. We analyzed the data of adult patients admitted with scrub typhus between March 2022 and February 2024, and their blood samples were evaluated with both IgM ELISA and DNA RT-PCR. The IgM antibody levels against Orientia tsutsugamushi were detected by ELISA and expressed as optical density (OD) values. The bacterial load was assessed by RT-PCR and presented as cycle threshold (CT) values. The OD values > 0.5 and CT values < 40 were deemed positive diagnoses for scrub typhus. The symptoms were weighed for their incidence and co-occurrence. We correlated the OD and CT values of the study population. The R software version 4.4.1 (R Foundation for Statistical Computing, Vienna, AUT) was utilized for data analysis.

RESULTS

Of the 231 patients scrutinized, 170 were deemed eligible. Sixty-five (38.2%) participants were female. The median age of the study subjects was 44.5 (24.0-61.8) years. All of them had fever. Other symptoms (in decreasing order of incidence) were as follows: cough (139, 81.8%), lymphadenopathy (29, 17.1%), rash (26, 15.3%), abdomen pain (18, 10.6%), eschar (6, 3.5%), and seizure (2, 1.2%). Maximum co-occurrence was observed between cough, lymphadenopathy, rash, and pain in the abdomen with fever. It held good for both females and males. The study population's median OD and CT values were 2.8 (0.8-3.7) and 41.0 (36.0-42.0), respectively. The OD and CT values were positively correlated (r = 0.78, 95% CI = 0.71-0.83, p < 0.001).

CONCLUSION

The study participants had symptoms like fever, cough, lymphadenopathy, rash, pain in the abdomen, and eschar. Our findings suggest that ELISA and DNA RT-PCR could be used for scrub typhus diagnosis among patients with febrile illness for > 5 and ≤ 5 days, respectively. Both diagnostic methods were found to possess a positive correlation. The findings of ELISA and DNA RT-PCR must be probed further.

Unravelling the Enigma of Scrub Typhus: A Critical Review and Insights Into Epidemiology, Clinical Features, Diagnostic Advances, and Emerging Trends

Scrub typhus (ST) is caused by the bacterium Orientia tsutsugamushi, which exhibits significant antigenic diversity and is prevalent in the Asia-Pacific region. Its clinical presentation is characterized by non-specific symptoms such as headache, myalgia, sweating, and vomiting, along with the abrupt onset of fever and chills. An eschar is often visible in the axilla, groin, or inguinal area and is present in around half of the confirmed cases. The Weil-Felix test is the earliest detection technique, though it is not highly specific. Diagnostic procedures include biopsy, culture, serology, and PCR. The molecularly detectable amount of Orientiae in the bloodstream occasionally reaches levels that are identified during acute illness and vanish after the first round of appropriate antibiotic treatment. This study offers a thorough review of ST, a disease carried by vectors caused by Orientia tsutsugamushi. We emphasize on the significance of monitoring and awareness campaigns, diagnostic problems, and geographical differences. It is essential to use multidisciplinary techniques combining epidemiologists, public health authorities, and doctors. Sustained observation and research are essential for developing successful preventative and control measures. When participating in outdoor activities in areas known for such infections or at particular times of the year when ticks or mites carry the rickettsia infection, people should take great precautions to prevent getting bitten by ticks or mites. Prompt medical evaluation is advised if suspicious symptoms or signs appear, especially in elderly individuals.