Girolamo Fracastoro may be credited with the development of germ theory, but if you read the Old Testament the Hebrew people seemed to have beaten him to the punch. Leviticus and Numbers are full of cleansing and purifying rituals, that we would recognize today as basic hygiene. It is almost as if God knew how to prevent communicable diseases for His chosen people while they were in exile...what are the odds?
Leviticus 15 is all about how to cleanse different bodily discharges, this is not merely an arbitrary set of rules made to teach obedience. It involved getting rid of any bedding or clothing the sick person or menstruating woman used, and bathing in clean water. This is the pre-antibiotic era form of disease prevention. Leviticus 13-14 deals with leprosy, and how to quarantine, clean, and care for this contagious destructive illness. God understood how germs were spread and gave laws to keep His people well.
God even tells them how to reduce the chance of spreading bloodborne pathogens from tribes that they warred against. Numbers 31:19-24 tells the Israelite soldiers to stay outside the camp after they battle so they can cleanse themselves and their plunder. They are to "purify every garment, every article of skin, all work of goats' hair, and every article of wood."(Num 31:20). And for every article of metal is to be purified with fire.
So next time you wash your hands after you sneeze, thank the Good Lord for hygiene.