The severe acute respiratory syndrome (SARS) is a serious, sometimes fatal, illness caused by a virus called coronavirus. First described in Asia in 2002, SARS was discovered in Chinese patients who had fever and severe breathing problems. In spring 2003, SARS quickly spread among humans with close person-to-person contact. More than 8000 people in Asia, Europe, and North and South America became sick with SARS. Some places, such as Hong Kong, set up emergency clinics to handle the large numbers of patients with the illness. Few studies have fully described what happened during the outbreak and the rapid spread of the infection.