Vaccines get all the glory, but most plumbers will tell you that it was water infrastructure – sewage systems and clean water – that eradicated disease, and they’re right.
Disease Before Plumbing
After the fall of the Roman Empire, Europeans despised all things Roman, including bathing. There was a widespread belief that getting wet caused illness. This contempt and fear of bathing persisted through the Dark Ages.
Some Europeans defied local customs by bathing, but this was usually done over great protest. When Queen Elizabeth bathed, her servants panicked, fearing she would become ill and die.
This resistance to bathing was brought across the Atlantic to America, influencing habits all the way into the 1800s. In 1835, Philadelphia almost passed an ordinance forbidding wintertime bathing. Ten years later, Boston did outlaw bathing, except by medical directive. (Though this law was not widely enforced, it does illustrate the American resistance to bathing as late as the mid 1800s.)
How Plumbing Eradicated Disease
Before plumbing was widely used, indoor facilities consisted of a washstand and a washbowl, a pitcher, and a chamber pot or commode. Human waste was thrown into the street or anywhere convenient.
This total lack of sanitation in urban areas filled with rats and other vermin provided the perfect environment to spread disease. The Black Plague alone killed 75 million – 200 million people – including 1/3 of Europe’s population. Though this disease is not entirely eradicated, human infection has become a rare occurrence. The last plague epidemic in America was in the early 1900’s.