On examination, the patient had a fever of 40.3°C. She was pale, but the examination was otherwise normal. There was no skin rash or lymphadenopathy. The hemoglobin level was 9.6 g/dL (mean corpuscular volume, 94.9 fL; mean corpuscular hemoglobin, 32.7 pg), and erythrocyte sedimentation rate was 130 mm/h. The peripheral blood picture was unremarkable. The serum lactate dehydrogenase level was elevated (1,315 U/L). Otherwise, renal and liver function test results were normal. Hospital admission chest radiograph and CT findings of the thorax, abdomen, and pelvis were normal. Antinuclear antibodies, rheumatoid factor, and anti-neutrophil cytoplasmic antibody were negative. No abnormal serum or urine monoclonal Ig was detected. Repeat cultures of blood, sputum, urine, and stool were negative. Malaria, typhoid, typhus, syphilis, brucellosis, leptospirosis, melioidosis, infections due to Mycoplasma, Chlamydia, Legionella, Rickettsia, HIV, hepatitis B virus, hepatitis C virus, and severe acute respiratory syndrome-coronavirus were excluded by appropriate tests. Transesophageal echocardiography did not show any vegetation on the heart valves. A Mantoux test showed a 10-mm induration. Bone marrow aspiration and trephine biopsy were done twice and revealed normal hematopoiesis, with no abnormal infiltrates.