I was in Hong Kong on a layover during the SARS outbreak and 80% of the population was wearing those mask. I was freaked out, so I called my sister who works at Ft Detrick, Md. She said while it's not a bad idea to wear a mask, the virus (SARS) was spread by physical contact. The most important thing to do is frequent hand washing with soap and water or use of an alcohol-based hand rub.