Causes of Severe Acute Respiratory Syndrome(SARS)
SARS is caused by a member of the coronavirus family of viruses (the same family that can cause the common cold). It is believed the 2003 epidemic started when the virus spread from small mammals in China.

When someone with SARS coughs or sneezes, infected droplets spray into the air. You can catch the SARS virus if you breathe in or touch these particles. The SARS virus may live on hands, tissues, and other surfaces for up to 6 hours in these droplets and up to 3 hours after the droplets have dried.

While the spread of droplets through close contact caused most of the early SARS cases, SARS might also spread by hands and other objects the droplets has touched. Airborne transmission is a real possibility in some cases. Live virus has even been found in the stool of people with SARS, where it has been shown to live for up to 4 days. The virus may be able to live for months or years when the temperature is below freezing.

With other coronaviruses, becoming infected and then getting sick again (reinfection) is common. This may also be the case with SARS.

Symptoms usually occur about 2 to 10 days after coming in contact with the virus. In some cases, SARS started sooner or later after first contact. People with active symptoms of illness are contagious. But it is not known for how long a person may be contagious before or after symptoms appear.