The growth of HIV is responsible for the resurgance of TB, as well as the development of resistant strains. Some of them now kill within a week (thankfully, these cases have been extremely rare, so far).
Things are more complicated than they may seem at first glance. Apparently, the letter informing him that he had the drug-resistent strain of TB didn’t reach him until he had already left for Europe. So on the first flight from the U.S. to Europe, he didn’t yet know. The other flights were foreign airlines in foreign countries, so it depends on their laws, and he would have to be extradited to them. Highly unlikely.
See QtM’s reply, and Inigo’s as well…we’re talking about the book “The Stand” by Stephen King, in which a military created superbug wipes out just about everybody, and then it gets strange after that.