Cholera is transmitted in two ways: unhygienic conditions or contaminated shellfish (particularly raw oysters). Marquez is Columbian and the book’s setting is somewhere in the Caribbean, so it may have been the Columbian coast. I suppose we shall learn how this early character helped stop a cholera epidemic there.
Of course, a new character has just been introduced – I had to look back to see if I’d heard of him before and I had not. So I’m not sure what that’s about.