A 23-year-old man is brought to the emergency department by his family due to a severe sore throat, persistent elevated fevers, pain and difficulty with swallowing, and shortness of breath. His symptoms worsened over the past day. Three days ago, he was seen at an urgent care center for pharyngitis and was prescribed azithromycin. The patient's past medical history is otherwise insignificant. He does not use tobacco, alcohol, or illicit drugs. His temperature is 40 C (104 F), blood pressure is 90/58 mm Hg, pulse is 115/min, and respirations are 24/min. Pulse oximetry shows 94% on room air. Physical examination is notable for a well-built man in moderate distress due to pain. There is mild swelling and erythema of the oropharynx and tonsils without exudate. Dentition is intact and shows good hygiene. The neck is swollen and tender along the left sternocleidomastoid muscle. Lung examination reveals basilar crackles. There are no heart murmurs. Leukocyte count is 17,400/mm³ with 93% neutrophils. A duplex ultrasound shows left internal jugular vein thrombosis. Chest x-ray reveals multiple peripheral lung nodules, some with cavitation. Which of the following is the most likely causative organism?

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Lemierre syndrome (LS) is a severe life-threatening infection that affects young immunocompetent patients and is usually caused by the gram-negative anaerobic bacillus Fusobacterium necrophorum. F necrophorum is part of the normal oral flora. LS usually begins with an oropharyngeal infection, usually tonsillitis, but can also arise as a complication from dental work or mastoiditis. The bacterium invades the lateral pharyngeal space through the lymphatic system and affects the neurovascular structures, causing internal jugular vein thrombosis and infection. The classic presentation is a prolonged (eg, weeklong) duration of sore throat with high fever, rigors, dysphagia, and neck pain and swelling along the sternocleidomastoid muscle. Once the internal jugular vein is infected, septic thromboemboli can seed other organs, particularly the lungs, causing respiratory symptoms and leading to nodules on chest x-ray. LS should be considered in any toxic-appearing patient with respiratory difficulties and significant neck swelling or tenderness in the week following an oropharyngeal infection. Microbiologic diagnosis requires culture from blood or pus. In addition to supportive (eg, airway) management, treatment is with intravenous antibiotics and, possibly, surgery (eg, incision and drainage, vein excision) in patients with no response to antibiotics. (Choice A) Clostridium perfringens is a gram-positive bacillus that commonly causes food poisoning and gas gangrene. (Choice C) Prior to the use of the conjugate vaccine against Haemophilus influenzae serotype b (Hib), the organism was an important cause of epiglottitis, which can present with febrile pharyngitis and progress to respiratory compromise. Hib infection can also lead to bacteremia. However, jugular vein thrombosis and septic pulmonary emboli are much more suggestive of LS due to Fusobacterium. (Choice D) Klebsiella pneumoniae is a gram-negative rod that is a rare cause of community-acquired pneumonia. A classic presentation is pneumonia with thick "currant jelly" sputum in alcoholics or patients with diabetes. (Choice E) Group A Streptococcus pyogenes causes many cases of bacterial pharyngitis. However, tonsillar exudates are classically present and patients are not typically severely toxic-appearing. Educational objective: Lemierre syndrome (LS) is caused by an oropharyngeal infection, usually pharyngitis or tonsillitis, that leads to local invasion of the lateral pharyngeal wall and infection of the neurovascular bundle, especially the internal jugular vein. Thrombosis of this vein allows dissemination of septic emboli to distal sites. Fusobacterium necrophorum is the most frequent bacterial cause of LS.

A 23-Year-Old Man Is Brought to the Emergency Department by His