Exactly how many people were infected or killed by her is not known. She refused to cooperate with health authorities, withheld information about her past, and used different pseudonyms when she changed cities. Three deaths have been definitively attributed to her, with estimates running as high as 50.[5]
Mallon was the first asymptomatic typhoid carrier to be identified by medical science, and there was no policy providing guidelines for handling the situation. Some difficulties surrounding her case stemmed from Mallon's vehement denial of her possible role, as she refused to acknowledge any connection between her working as a cook and the typhoid cases. Mallon maintained that she was perfectly healthy, had never had typhoid fever, and could not be the source. Public-health authorities determined that permanent quarantine was the only way to prevent Mallon from causing significant future typhoid outbreaks.[citation needed]
Other healthy typhoid carriers identified in the first quarter of the 20th century include Tony Labella, an Italian immigrant, presumed to have caused over 100 cases (with five deaths); an Adirondack guide dubbed "Typhoid John", presumed to have infected 36 people (with two deaths); and Alphonse Cotils, a restaurateur and bakery owner.[citation needed]
Today, "Typhoid Mary" is a colloquial term for anyone who, knowingly or not, spreads something undesirable.[12]
In August 2013, researchers at the Stanford University School of Medicine announced they were making breakthroughs in understanding the exact science behind asymptomatic carriers such as Mallon. The bacteria that causes typhoid may hide in macrophages, a type of immune cell.[13][14]
Individuals can develop typhoid fever after ingesting food or water contaminated during handling by a human carrier. The human carrier may be a healthy person who has survived a previous episode of typhoid fever yet who continues to shed the associated bacteria, Salmonella typhi, in feces and urine. Washing hands with soap before touching or preparing food, washing dishes and utensils with soap and water, and only eating cooked food are all ways to reduce the risk of typhoid infection.[15]
