The global population is about 6.5 billion. The approximate number of SARS cases is 5000, mostly in a few specific geograpical areas. That gives you a rough chance of 1 in 1.3 million of actually contracting SARS. The odds will obviously increase if you visit one of the high risk areas or decrease if you're in an area with no reported cases. If you're not headed to Asia, stop worrying.

My $.02

Ed