More than a decade and a half ago, in another life, I was concerned with transmission of viral diseases (from a bioterror not a pubic health perspective). There was a classic study showing folks in a hospital getting sick a few rooms down from an infected patient -- hvac issues with a virus, forget which it was. Since then, most hospitals have curtailed hvac systems that go room to room, I assume nursing homes have too, but they are often privately owned and seem to care more about profits than patients, imo.