Cholera seems to have existed in the Ganges delta for a long time, but it only spread to the rest of the world fairly recently, Gregory Cochran notes, and two factors interfered with an effective policy response:
[Scientists] concluded that contagion was never the answer, and accepted miasmas as the cause, a theory which is too stupid to be interesting. Sheesh, they taught the kids in medical school that measles wasn’t catching — while ordinary people knew perfectly well that it was. You know, esoteric, non-intuitive truths have a certain appeal — once initiated, you’re no longer one of the rubes. Of course, the simplest and most common way of producing an esoteric truth is to just make it up.
On the other hand, 19th century liberals (somewhat like modern libertarians, but way less crazy) knew that trade and individual freedom were always good things, by definition, so they also opposed quarantines — worse than wrong, old-fashioned! And more common in southern, Catholic, Europe: enough said! So, between wrong science and classical liberalism, medical reformers spent many years trying to eliminate the reactionary quarantine rules that still existed in Mediterranean ports.
The intellectual tide turned: first heroes like John Snow, and Peter Panum, later titans like Pasteur and Koch. Contagionism made a comeback.