Diagnosing scrub typhus without eschar: a case report using metagenomic next-generation sequencing (mNGS)

Scrub typhus is a disease caused by the bacteria, Orientia tsutsugamushi, which is spread to people through the bites of infected larval mites. Symptoms include eschar at the place of infection, as well as many flu-like symptoms, e.g., fever, headache, chills and skin rash. As eschar is the most typical symptom of scrub typhus, it is often used to diagnose the disease, but if a patient does not display an obvious eschar lesion, diagnosing the disease can prove to be difficult. To help improve the diagnoses of scrub typhus, metagenomic next-generation sequencing (mNGS) has been used as a new approach to identifying pathogens. Here, we report a 51-year-old patient who had unexplained fever for a week and was admitted to hospital with no obvious eschar on her body. Smears and cultures of blood and sputum samples were first performed, but all returned a negative result for scrub typhus. We then conducted a mNGS analysis of blood and sputum samples and were able to identify the pathogenic microbe. Subsequently, a total of 377 reads, as well as 12 unique reads of Orientia tsutsugamushi were detected in the patient's blood and sputum. Quantitative polymerase chain reaction (qPCR) results of blood samples further confirmed our mNGS detection, suggesting that the patient did indeed have scrub typhus. From these results, we determined that mNGS as a diagnostic tool provides a better method of identifying clinical febrile pathogens with atypical characteristics.