It’s not even controversial to say that both simple minded Germ theory and terrain theory are false. For an example of the former, see meningitis and for the later the eradication of small pox and virtual eradication of polio. It’s fair to say both play a part. Case in point, in the before times, when it was flu season, a flu would start off in one end of the office, successively spread to surrounding cubicles over the next week (germ theory), jump over me (terrain theory), and continue on to the people after me until it made its rounds around the office (germ theory). I would rarely ever get colds even when surrounded with people with colds (terrain theory), but if my throat got extremely dry and my feet were cold or I was under a lot of stress, I would get sick if I didn’t “fix” it in time (terrain theory). My father was the same way. When I eventually did get sick, I got sicker than anyone else in the office…it was impossible to hide. But I went to work, no-one else would get sick. Why? I told people I was sick and told them to back off, and I wore a scarf, and tried not to touch anything everyone else did (germ theory). Both theories are very compatible and generally agreed upon as long as you don’t go off the deep end on either side.