A 15-year-old girl was admitted with a high fever and progressive malaise, vomiting, anorexia and abdominal complaints. She previously had a sore throat and unilateral painful swollen lymph nodes in the neck. Laboratory investigation indicated a bacterial infection. Blood cultures were taken. There was infiltrate in the left lung. Pneumonia complicated with sepsis was suspected and ceftriaxone was started. The patient's condition deteriorated. Computed tomography (CT) scan showed progressive infiltrates in both lungs and pleural effusion. Blood culture led to the diagnosis. After changing antibiotics the patient slowly improved. Antibiotics were continued for several weeks.