Severe acute respiratory syndrome (SARS) is an infectious disease caused by a virus called coronavirus. SARS can spread quickly from person to person and cause large outbreaks. Symptoms, including fever, body aches and pains, cough, and trouble breathing, may progress rapidly. Patients with severe pneumonia-like symptoms sometimes need machines to help them breathe. About 10% may die. Much of the information related to symptoms caused by SARS comes from studies of patients who were hospitalized for pneumonia. We do not know whether some patients infected with the SARS coronavirus have only mild or no symptoms.