By the 1850s, "Sanitationists" such as Florence Nightingale had correlated cholera and many other diseases with dirty water and dirty people, but they were unaware of the specific means of transmission of various diseases. They knew that alcoholic beverages were usually safer than water, but they didn't know that a tot of gin in a gallon of water would make it safe to drink. They knew that boiling clothes and sheets would kill vermin and reduce disease, but they didn't know that boiling also kills germs in water or on surfaces.
The failure of medical science of the time to make that connection would cost the Lincoln family a son a few years later.