http://www.cbsnews.com/news/noroviru...rough-the-air/
To summarize- researchers measured concentrations of airborne Norovirus in hospitals at 1 meter from a Norovirus patient, at the patient door, and at nursing stations. A majority of those sites had significant concentrations of Norovirus to infect a person. Per the article, it's still unknown whether actual transmission via airborne particles is possible or not. Although researchers hypothesize airborne transmission explains why outbreaks are so hard to contain.
To editorialize- another reason to avoid shelters.