The story of the real Typhoid Mary - In the early 1900s, germ theory was a relatively new concept, and many – including doctors – were unaware of how diseases spread. At the time, bacterial diseases like typhoid and dysentery could still wipe out an entire family. Mary Mallon was an Irish immigrant who worked as a cook for affluent New York families. In her wake, she unknowingly left an outburst of typhoid fever, earning her the epithet "Typhoid Mary." By that time, doctors knew the disease was most commonly spread through excrement, and they were able to trace outbreaks by locating the start of an epidemic and following its spread.