Low back pain with fever

A 70-year-old man presented with lower back pain for 10 days. 15 days before pain onset, he had a low-grade fever, chills, and asthenia, and 4 days before admission, he had constipation, malaise, generalized weakness, anorexia, nausea, and vomiting. On admission, the patient was afebrile and hypotensive, with a heart rate of 105 beats/minute and an oxyhaemoglobin saturation on room air of 95%. Hyponatremia, lymphopenia, elevated C-reactive protein and ferritin were observed in complementary tests. Computed tomography (CT) scan was performed. The patient tested negative by reverse transcription-polymerase chain reaction (RT-PCR) of the nasopharyngeal swab, yet positive for IgG and IgM by ELISA.