An Irish immigrant cook, Mallon became the focus of one of the best-known episodes in the history of communicable disease when U.S. health officials identified her as a healthy carrier of the organism causing typhoid fever. Mallon, who refused to acknowledge her role in spreading the disease as a cook, is known to have infected at least 53 people, resulting in three deaths. Unable to stop her from cooking for others, New York City authorities confined her for 26 years on North Brother Island in the East River.

Prior to Mallon, authorities including Robert Koch and Walter Reed had speculated that the disease might be spread by carriers who transmitted typhoid bacteria even though they looked and felt perfectly well. Mallon became the first healthy carrier to be positively identified by U.S. health officials, when she was tracked down by George Soper, an epidemiologist and sanitary engineer from...