Queen Elizabeth II left the London hospital where she\'d been treated for the symptoms of a stomach infection Monday, following a brief and rare hospitalization for the 86-year-old head of state, AP reported. A smiling Elizabeth walked unassisted out of King Edward VII Hospital Monday afternoon before saying goodbye to staff. She was then driven away in a motorcade. \'The queen has left the King Edward VII\'s Hospital having been admitted briefly as part of the assessment of symptoms of gastroenteritis,\' the palace said in a brief statement issued after her release. Gastroenteritis is an inflammation of the stomach and/or the intestine, generally caused either by food poisoning or the norovirus, a common winter vomiting bug that affects several hundred thousand Britons every year. The queen has canceled engagements for this week due to the illness. It was her first hospitalization in 10 years.