Case Presentation: A 75-year-old woman presented to our hospital with general fatigue as her chief complaint. She had experienced fatigue for four days prior to admission and developed a fever three days earlier, prompting her to visit a prior doctor. Initial blood tests revealed leukopenia, and she was prescribed antibiotics and antipyretics. However, as the fever persisted, she revisited the previous doctor, where follow-up tests showed her white blood cell count had dropped further to 1100/μl, and her platelet count had decreased significantly to 134,000/μl. The patient was subsequently referred to the emergency department. On arrival, she had a fever of 102.4 °F, but other vital signs were stable. Physical examination revealed splenomegaly but no palpable superficial lymph nodes, rashes, or visible insect bite marks. Treatment was initiated for febrile neutropenia upon admission, but the fever persisted. By the sixth day of hospitalization, the patient developed altered mental status and disseminated intravascular coagulation. A bone marrow aspiration was performed on day 7 due to ongoing fever, splenomegaly, and progressive thrombocytopenia (42,000/μl), confirming a diagnosis of hemophagocytic syndrome (HPS). Further investigation into the cause of cytopenia revealed severe fever with thrombocytopenia syndrome (SFTS) virus in her serum, throat swabs, and urine, confirming SFTS. Multidisciplinary treatment in the ICU led to improvement in her platelet counts by day 8 and resolution of the fever to a low grade. However, severed hyperactive delirium persisted until day 13, necessitating intravenous sedative management. The patient was eventually transferred to the general ward and discharged on day 38.
Discussion: SFTS, a tick-borne viral infection, has seen rising incidence rates, particularly in Asia. Globalization and climate change have contributed to the expansion of regions where SFTS can occur and the reduction of its seasonal limitation. While diagnosis is typically straightforward in patients with a history of tick bites, especially during farming or outdoor activities, cases like this one—where there is no clear bite history or visible bite marks—present a diagnostic challenge. Although the patient’s initial history and physical findings did not suggest a tick-borne viral infection, SFTS was considered after ruling out other causes of persistent fever and thrombocytopenia. This consideration was further supported by the increasing prevalence of tick-related diseases in the region. Additionally, this case highlights an unusual presentation of prolonged hyperactive delirium associated with severe SFTS, a rare but notable feature. While altered mental status is a recognized complication of SFTS, this case emphasizes the need for clinicians to consider neurological symptoms as part of the disease’s spectrum.
Conclusions: This case illustrates the challenges of diagnosing SFTS in the absence of clear exposure history or visible bite marks. Clinicians in endemic regions should remain vigilant for tick-borne infections in patients presenting with persistent fever, thrombocytopenia, and splenomegaly, even when typical exposure risk factors are not present. The unique presentation of prolonged delirium in this patient highlights the importance of comprehensive management and the need for intensive care and infection control strategies in severe cases.