A 15-year-old girl is brought to the physician because of a 3-day history of severe pain and swelling in her right stemoclavicular joint. Ten days ago. the patient had a sore throat. She has no history of serious illness and takes no medications. Her temperature is 40°C (104°F). Examination shows erythema, swelling, and tenderness of the right stmnoclavicular joint. Aspiration of the affected joint yields thick, yellow, purulent fluid. A Gram stain of the fluid shows numerous segmented neutrophils and numerous gram-negative diplococci.