Mary Mallon Is Identified as a Healthy Typhoid Carrier

In the late summer of 1906, an outbreak of typhoid fever struck the summer residence of a New York banker in Oyster Bay, Long Island. Six of the eleven people in the household fell ill, alarming the property owner, who feared the estate would become unrentable. To investigate the source of the infection, he hired George Soper, a sanitary engineer. After ruling out typical environmental sources such as contaminated water and milk supplies, Soper focused on the domestic staff. His attention turned to Mary Mallon, an Irish-born cook who had joined the household shortly before the illness appeared and departed three weeks after the outbreak began.

Mallon, who had emigrated to the United States around 1883, had established a successful career cooking for affluent families across the New York region. Tracing her work history through an employment agency, Soper identified twenty-two cases of typhoid across seven households where she had previously cooked. Knowing from European medical research that people could carry and shed pathogens without exhibiting outward symptoms, Soper hypothesized that Mallon was an asymptomatic carrier of the bacteria causing typhoid fever. When he confronted her in March 1907 to request biological samples, Mallon, convinced of her own robust health, angrily drove him away with a carving fork.