When I was a 19 year old student, my landlady came back from rural northern pakistan with "cold". Of the three students in the house, the girl who had travelled across asia was ill in bed for 3 days, the other had asthma and ended up in hospital after a fortnight of illness and missed the rest of term. I moved out straight after the landlady came back. After a week in the new house I became ill. The new house mate just thought I was quiet. I was lying my room with a fever that bad I was hallcenating demons coming out of the walls. I choked a few times, losing conscieceness once. I knew at the time what I had could kill, so I quarentined myself. Luckly my new housemate was abit aspergic, and would only drink and eat from his cups and plates, wiped the door handles with bleach, and had very habitual way of doing things. He never got ill.
I got ill because my immunue system wasn't educated to deal with it, I survived because of luck. Considering it had a 10 day incubation period the rest of the population was lucky too.
What doesn't kill you makes you stronger.