Avoiding illness is easier than later treatment. Washing one's body and teeth has grown nearly universal, as were becoming more aware of disease prevention. What our forefathers and even our grandparents did or didn’t do is very different from what we do now or, at least, what we should do.
A well-mannered person is a healthy person. You should leave everything forbidden by the rules of a good upbringing aside as something that promotes an unhealthy lifestyle.
Dirty hands, fingernails and laundry, and unaired rooms are deficiencies often caused by thoughtlessness or bad habits and can be the source of frequent illness. People who spit on the street, in public transport or in living quarters are not merely ill-mannered, but also facilitate transfer of diseases. People who cough or blow their noses without holding a tissue in front, can easily transfer their runny nose, cough, flu, pneumonia, or even more severe diseases to people nearby. Small children are especially sensitive to such exposure. We can give you hundreds of similar examples.
People who take care of their hygiene daily, who are outdoors as much as possible, and who air their home at least once a week, can be sure of their safety. They can be certain that they are adding years to their lives, that they are more productive, willful and, certainly, more vital.