Lemierre syndrome is a rare and potentially severe complication of bacterial infections that usually affects previously-healthy adolescents and young adults. It most commonly develops in association with a bacterial throat infection, but it may develop in association with an infection involving the ears, salivary glands (parotitis), sinuses, or teeth; or in association with an Epstein-Barr infection. The bacteria typically responsible for infection in Lemierre syndrome is Fusobacterium necrophorum, although a variety of bacteria can be responsible. In people with Lemierre syndrome, the initial infection spreads into tissues and deep spaces within the neck, leading to the formation of an infected blot clot (septic thrombophlebitis), sometimes made up of pus, in the internal jugular vein (the blood vessel that carries blood away from the brain, face, and neck). The infected clot then circulates in the blood (septicemia), resulting in the infection also spreading to the lungs (most commonly), skeletal system, and/or other parts of the body such as the spleen, liver, kidney, heart, or brain. This can lead to severe complications such as respiratory distress syndrome due to pulmonary emboli (blood clots in the lung), damage to other affected organs, and/or septic shock (in about 7% of cases). Lemierre syndrome may be diagnosed based on signs and symptoms, various blood tests, and imaging studies.