The incubation period of SARS is usually 2-7 days but may be as long as 10 days.
The first symptom of the illness is generally fever (>38°C), which is often high, and sometimes associated with chills and rigors. It may also be accompanied by other symptoms including headache, malaise, and muscle pain. At the onset of illness, some cases have mild respiratory symptoms. Typically, rash and neurologic or gastrointestinal findings are absent, although a few patients have reported diarrhoea during the early febrile stage.
After 3-7 days, a lower respiratory phase begins with the onset of a dry, non-productive cough or dyspnoea (shortness of breath) that may be accompanied by, or progress to, hypoxemia (low blood oxygen levels). In 10–20% of cases, the respiratory illness is severe enough to require intubation and mechanical ventilation. Chest radiographs may be normal throughout the course of illness, though not for all patients. The white blood cell count is often decreased early in the disease, and many people have low platelet counts at the peak of the disease.
Source: World Heath Organisation