Assuming people make the connection between unclean/unchanged water and the infection. People in general didn't have the same kind of understanding of disease back then (or until the 20th century really) and very few people would consider the possibility (The account I read about comes from someone who did). They would just blame it on the gods or something. I mean it's bathwater, surely it's fine. I'm not getting sick. And no one is dying in that other public bath a few blocks over. And he didn't get really sick until a few days later anyway so it can't be the baths. Obviously he angered one of the gods with his unvirtuous behaviour. =P