Typoid is a disease that inflames the intenstines. It is spread through contact with the infection, so can be carried in water, or passed on through contact with an infected person.
Poor water supplies in the 19th century meant that the disease could spread easily around cities. It was a disease that claimed many lives, including the lives of several wealthy people: Pronce Albert, Queen Victoria’s husband, for example.
There are known cases of apparently healthy humans carrying the disease and passing it on through their contact with people, water or food. One of the best known Typhoid carriers was mary mallon, and irish migrant to America who became known as Typhoid Mary. Her story can be read on the wikipedia website by following this link.