SARS (severe acute respiratory syndrome) is a new respiratory illness that has been reported in Asia, North America, and Europe. SARS appears to spread primarily by close person-to-person contact with symptomatic individuals (e.g., persons with fever or respiratory symptoms). SARS can be spread by touching the skin of other people or objects contaminated with infectious droplets and then touching the eyes, nose, or mouth. Contamination occurs when someone with SARS coughs or sneezes droplets onto themselves, other people, or nearby surfaces. It also is possible that SARS can be spread further through the air by very small particles. This method is called airborne transmission, but investigations to date suggest that this type of transmission is unusual. It also is possible that SARS may be spread by other ways that are currently not known.
Respirators that filter out at least 95% of airborne particles during “worse case” testing using a “most-penetrating” sized particle are given a 95 rating. Those that filter out at least 99% receive a “99” rating. And those that filter at least 99.97% (essentially 100%) receive a “100” rating.
Respirators in this family are rated as N, R, or P for protection against oils. This rating is important in industry because some industrial oils can degrade the filter performance so it doesn’t filter properly.* Respirators are rated “N,” if they are Not resistant to oil, “R” if somewhat Resistant to oil, and “P” if strongly resistant (oil Proof). Thus, there are nine types of disposable particulate respirators:
N-95, N-99, and N-100;
R-95, R-99, and R-100;
P-95, P-99, and P-100.
Both CDC and the World Health Organization (WHO) recommend respirator use for the following workers only:
health care workers entering the room of a patient with SARS
medical transport workers transporting patients with suspected SARS
Respirators are not routinely needed (by staff or visitors) in other parts of hospitals or other health care facilities where there is no direct contact with patients.
Outside the health care and medical transport settings, CDC does not recommend the routine use of respirators. Most people who develop SARS become infected through contact with other people who are ill with SARS, not by breathing contaminated air. If a person does contact the SARS virus, it is most likely to be on a surface such as a door knob. The best protection from SARS in public places, (including workplaces other than health care and medical transport settings) is to wash your hands frequently and avoid touching your eyes or nose.
https://www.cdc.gov/niosh/npptl/topi.../respsars.html