SARS is caused by a coronavirus called SARS-associated coronavirus (SARS-CoV). SARS-CoV is thought to be transmitted most readily by respiratory droplets produced when a person infected with SARS-CoV coughs or sneezes and the droplets are transmitted through the air and deposited in the mucous membranes of the mouth, nose, or eyes of nearby individuals. The virus can also be transmitted by touching a surface or object contaminated with infectious droplets and then touching the mouth, nose, or eyes. Other modes of transmission are still under investigation. Because SARS was unknown before 2003, no seasonal pattern of transmission has been described. It’s known that other viral respiratory infections recur seasonally, however, which increases the probability of a similar pattern for SARS.

Complications of SARS are related to the associated symptoms. The majority of the patients infected with the SARS virus develop pneumonia. Dehydration may occur related to fever and diarrhea. About 10% to 20% of patients develop severe respiratory symptoms and hypoxemia, necessitating mechanical ventilation. Fatality is estimated to be 13% for patients younger than age 60 and 43% for patients older than age 60.

The patient may report a prodrome of fever of 100.4° F (38° C), often accompanied by chills and rigors. He may also complain of headache, malaise, and myalgias. The incubation period for SARS is typically 2 to 7 days, but has been reported to be as long as 10 days. At the initial onset of symptoms, mild respiratory symptoms are common, and diarrhea has been reported during the febrile prodrome. After about 3 to 7 days, lower respiratory symptoms are assessed and often include a dry, nonproductive cough and dyspnea which may progress to hypoxemia. Mechanical ventilation may be required depending upon the severity of the hypoxemia and respiratory symptoms. The development of pneumonia is common.