Mary Mallon (1870-1938), an Irish-born cook employed in a home in Oyster Bay, Long Island, New York, was suspected of being a typhoid carrier as early as 1904. She ran away from authorities and was not captured until 1907. She spent almost all of the rest of her life confined in Riverside Hospital on North Brother Island, New York City. She herself was immune to typhoid but she transmitted the disease (through her handling of food) to atleast 50 people.
Today, a "Typhoid Mary" is anyone who is suspected of being a carrier of anything unpleasant, harmful or even disastrous; therefore, someone who is to be shunned. Most often the term is used jocularly, as when one pretends to shrink from a person who may have been employed by two companies that went bankrupt.
Facts on File Dictionary of Cultural and Historical Allusions.
