SARS is a severe respiratory disease that was first recognized in human beings in 2003. SARS stands for severe acute respiratory syndrome. SARS begins with a high fever followed by such symptoms as a cough and difficulty breathing. Some cases progress to pneumonia and respiratory failure. More than 6 percent of those who developed SARS have died.

The first outbreak of SARS occurred in southeastern China in November 2002. However, scientists initially thought it was a type of influenza, and it was not recognized as a new disease for several months. SARS was recognized only after cases appeared in Hong Kong. By then, the disease had already spread to several countries. Scientists believe that SARS is usually transmitted through close contact with infected patients. Many cases have occurred among health care workers.

Scientists identified the likely cause of SARS as a previously unrecognized variety of coronavirus. In human beings, coronaviruses are among the many viruses that cause common colds. Other types of coronaviruses cause serious or fatal disease in livestock, such as hogs, cattle, and chickens. However, the SARS coronavirus appears unrelated to the varieties of virus that infect livestock or cause colds in human beings. Scientists have found that the SARS virus closely resembles a coronavirus found in civets, catlike mammals often eaten as a delicacy in China. But scientists do not know precisely where or how the SARS virus originated.

Arnold S. Monto, M.D., Professor of Epidemiology, School of Public Health, University of Michigan. -