Final answer:
Typhoid Mary was returned to North Brotherly Island because she did not comply with the condition to never work with food again. She continued to work as a cook, leading to new cases and deaths from typhoid fever. Epidemiologists traced 51 cases and three deaths directly to Mary Mallon.
Step-by-step explanation:
Typhoid Mary was ultimately returned to North Brotherly Island because she did not comply with the condition set by the New York health department that she never again work with food. Despite being released from isolation in 1910, Mary Mallon continued to work as a cook, leading to new cases of typhoid fever and deaths. The authorities tracked her down again and returned her to isolation, where she remained until her death in 1938.
Epidemiologists traced 51 cases of typhoid fever and three deaths directly to Mary Mallon, establishing her as the source of the illness. Mallon, who was an asymptomatic carrier of the typhoid bacteria, unknowingly spread the infection to people with whom she was in close contact, mainly through food she prepared.