Mary Mallon, also known as "Typhoid Mary"

Typhoid Mary's tragic tale exposed the health impacts of 'super-spreaders'

Tracking down the culprit behind an outbreak of typhoid fever in 1900s New York was a breakthrough in how symptom-free carriers can spread sickness.

An Irish cook named Mary Mallon was the first person identified as being the carrier in a typhoid outbreak. The media dubbed her "Typhoid Mary," and her trial and forced quarantine captured public attention. In this illustration, published around 1909, she is depicted breaking skulls into a skillet.

Chronicle, Alamy

George Soper was not your typical detective. He was a civil engineer by training, but had become something of an expert in sanitation. So when, in 1906, a landlord in Long Island was struggling to trace the source of a typhoid outbreak, Soper was called in. The landlord had rented his Long Island house to a banker’s family and servants that summer. By late August, six of the house’s 11 inhabitants had fallen ill with typhoid fever.

Soper had been previously hired by New York state to investigate disease outbreaks—“I was called an epidemic fighter,” he later wrote—and believed that typhoid could be spread by one person serving as a carrier. In Long Island, he focused his attention on

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