Duncan went to the hospital, was tuned away, and came back days later. He theoretically could have infected a ton of people if he wanted to.
Agreed - I am really surpised that he didn’t infect people. Although he WAS feeling so lousy that first visit he probably just went back to the apartment and bed. His relatives said he kept to himself, cleaned up after himself in the bathroom, etc.
But - he was probably sick enough that he would not have considered getting on an airplane to plan a wedding.