Fever and acute urticaria in a young male patient

A 23-year-old man presented to our emergency department with a new onset of low-grade fever associated with diffuse itching urticarial rash localized to his trunk and upper limbs. He denied respiratory and gastrointestinal symptoms. Peripheral oxygen saturation was 98% at room ambient. His past medical history was unremarkable, and he was not taking any medications. No history of allergies was reported. He denied traveling abroad, contact with animals, ingesting raw meat or fish, or taking medicine. Laboratory results showed leukopenia with lymphocytopenia and normal C-reactive protein value. Eosinophils were normal. Hepatic and renal tests were all within the normal range. He was vaccinated with 3 doses of Comirnaty vaccine with no adverse reactions. Lung ultrasound showed A pattern without pleural effusion. The patient was discharged with oral steroids (prednisone 25 mg for three days with a progressive reduction in 10 days) and oral antihistamine (bilastine 10 mg daily for 10 days), and acetaminophen 1 gr if fever above 37.5°C, with complete resolution of the rash without sequelae in 10 days.