From a Prince of Wales Hospital Ward Manager:

From a Prince of Wales Hospital Ward Manager: It is more important to use hand sanitizer/wash hands than to wear a mask - no matter what kind of pneumonia, it is contagious by droplets. Because the droplets are heavy, they are not airborne, so chances are low that people will breathe these bacteria directly into the body. But the bacteria from the droplets can stay on the surface of any public object for 24 hours and still be active, including elevator buttons, any handrails, and even the salt/pepper/seasoning racks in restaurants. Studies have shown that an average person touches the face 10 times every hour (fixing glasses, squinting eyes, blowing your nose). Once your hands are contaminated and you touch your eyes/nose/mouth, you will be at risk. This is also why in the early stage of SARS, even though medical staff wore N95 masks they still contracted the disease.

Sanitizing and washing your hands often is more important.