What causes the bacteria to grow in some people and not other?

My mother was just diagnosed with MAC, having "the cough" for awhile now. After researching the internet all over the world on this bacteria culprit, I am trying to find out why the cilia in the lungs get damaged and allow this bacteria to invade. This bacteria is everywhere (water,soil) mostly. What has happened that people are getting this a lot NOW? Can anyone answer these three questions so that we may link WHY this bacteria may be getting stronger for some, please. There has been a 30% increase of the diagnosis of MAC in the last 20 years. It seems to be a large number of small, petite white woman, getting diagnosed between the ages of 61-17, in the little bit of studies that have done. I want to find the connection! I am also in the medical field, and don't want MAC when I get to 61 years old. (10 years)

Have you ever smoked? how long? when did you quit?
Have you ever been an RN, or worked in the medical field?
Have you ever had whooping cough?
What part of the country were you raised?