The current Western Medicine theory of disease, germ theory, is that “microorganisms known as pathogens or "germs" can lead to disease” (Wikipedia).
Unani Tibb medicine agrees that microorganisms exist but suggests that it is the imbalance of temperament that provides an altered environment in which these microorganisms are able to exist and proliferate.
A temperament becomes imbalanced when elements of life, such as air quality, stress, food, drink, sleep, rest and activity patterns, and exercise are imbalanced.
So embedded is the germ theory in modern culture that we often discount causative factors outside this theory (or, indeed, understand that it is one of many theories of disease).