If you think about it it's not really that wired. The MC was in different areas so he could have gotten exposed to a virus that was only in a area that he was in on Dozers route. its been a while since I started Dozers route I don't remember if the MC gets sick from a virus or not but I think you go to the library to help Dozer before this so the MC may have came in contact with a virus around that point.