Even if he did not have a life threatening illness or disease, once a person is sick, it would be nice if they stayed home to be sick, instead of sharing it. I've sometimes called in with mild symptoms, rather than taking it to work and sharing it. Taking care of myself while the cold or flu is mild sometimes prevents it from getting severe.
Yes, workplace ‘Typhoid Marys’ are prevalent these days. I know we are supposed to share...but not THIS.