989 Orientia tsutsugamushi: an emerging major cause of acute encephalitis syndrome in south Asian children

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<h3>Background</h3> Acute Encephalitis Syndrome (AES) is a major seasonal public health problem in several states of India. The National Vector-borne Disease Control Program (NVBDCP, India) reported &gt;75,000 cases of AES in India during 2014–2020 along with 6,912 deaths due to AES. Burden and mortality of AES cases continues to be high, and definitive etiologies for the illness have yet to be identified. <h3>Objectives</h3> The study was undertaken to identify the specific etiology of AES among children in a tertiary care hospital in India and to determine the contribution of <i>Orientia tsutsugamushi,</i> the agent of scrub typhus, as a cause of AES. <h3>Methods</h3> This hospital-based observational study was conducted over a 18-month period(1st July, 2019 to 31st December, 2020) among children between 1 month to 12 years of age. Cerebro-spinal fluid and/or serum samples were collected from a total of 552 consecutive hospitalized patients of AES and tested for various pathogens by Gram stain, culture and antibody testing by ELISA. <h3>Results</h3> Out of 552 enrolled patients, 251 (45.5%) were positive for at least one pathogen and 3 were co-positive for more than one pathogen. Maximum number of samples were positive for Scrub typhus IgM (24.6%, n=136). 10.5% of AES cases were due to pyogenic meningitis. Positivity for <i>M. tuberculosis</i>, HSV-1, Dengue virus and Mumps virus was found in 2.9%, 2.17%, 1.45% and 1.1% cases respectively. Occasional presence of Japanese encephalitis B virus, Varicella zoster virus, Corynebacterium diphtheriae and Salmonella typhi was also noted. Neuro-imaging and antibody testing were suggestive of acute disseminated encephalomyelitis in 9 (1.6%) and autoimmune encephalitis in 2 patients. The main clinical features of the 136 scrub typhus positive patients were fever(100%), altered sensorium(100%), headache(61.7%), seizures(51.5%), nausea(32.35%), neck rigidity(7.35%), limb weakness(6.6%) and cranial nerve palsy(4.4%). Eschar could be located in only 12.5% patients. Case fatality rate was 2.9%. <h3>Conclusions</h3> Our findings suggest emergence of <i>Orientia tsutsugamushi</i> as a notable causative agent of AES in this South Asian country. Similar results were obtained in several other studies from different parts of the country in recent years. As most of the clinical and laboratory features of scrub typhus are non-specific, clinicians need a high index of suspicion for detecting this neglected but easily treatable disease in cases with AES, at least in endemic areas.