I agree with MANmom. It is said to "run in families", which I believe is the term used when we think it's genetic, but it's yet to be proven.
However, can an infection TRIGGER it? Or can an infection speed up the degenerative process enough to hasten the onset of symptoms? Probablty. Stress is also a major factor. Pregnancy. Childbirth. Other trauma.
However, I think it's basically an accident waiting to happen...there's no way to avoid the things that might set it off.
I doubt it, it tends to run in families...my dad had it, two brothers (so far) have it, I had it plus cancer, my sister had same cancer, another sister has nodules that are being watched. All Hashi's cases surfaced in late 40's or 50's.