A Case of Japanese Spotted Fever Misdiagnosed as COVID-19 on Admission

COVID-19 is manifested by various symptoms and needs to be distinguished from other diseases. We report the case of a patient with Japanese spotted fever (JSF) who was admitted with a diagnosis of COVID-19. The patient was a 72-year-old woman with high fever whose SARS-CoV-2 rapid antigen test was positive. She also had rashes on her trunk and extremities, including on her palms and soles. We treated her as a COVID-19 patient, viewing her rashes as a complication of COVID-19 or a drug eruption. However, her fever and rashes persisted. Her medical history revealed a history of mowing, which involves a high risk of tick bites, and we discovered an eschar on her left popliteal fossa. We then suspected JSF and treated her with intravenous minocycline and levofloxacin as a severe case. PCR testing of specimens from the eschar was positive for Rickettsia japonica. A confirmatory SARS-CoV-2 PCR test and an anti-nucleocapsid antibody test were negative. We ultimately diagnosed the patient with JSF, not COVID-19. The number of JSF patients in Japan has increased in recent years. Since the clinical presentation of JSF patients and COVID-19 patients is similar, a careful medical history and physical examination are necessary to make the differential diagnosis.