Typhoid Mary. The name alone has become a myth, a terrible legend of a woman who carried disease with her wherever she went and killed the people around her, even though she never displayed a single symptom herself. The real Typhoid Mary died 75 years ago, but her cruel nickname has lived on. Today we all too often refer to anyone who brings a virus to our schools or workplaces as a "Typhoid Mary." But the truth about the real Typhoid Mary is much less deadly — and much more tragic — than the legend would have us believe.

Mary Mallon, the woman whose name would later become synonymous with disease, was born in 1869 in Cookstown, Ireland. She emigrated to the United States 15 years later and in her adulthood worked as a cook for several families in and around New York City. That was where her troubles began. Unbeknownst to anyone at the time, Mary was carrying a variation of the Salmonella bacteria. Although she did not display any symptoms, she passed these bacteria on to the people who ate her meals between 1900 and 1906. Dozens of them contracted typhoid fever, a disease that at its various stages causes high fever, delirium, diarrhea, intestinal hemorrhaging, encephalitis (a swelling of the brain) and significant damage to other organs.

Of course, none of these families were initially in contact, so the connection between their illnesses was not known for several years. That changed in 1906 when the family of banker Charles Henry Warren contracted typhoid fever while staying at a summer rental home on Long Island. Fearing that the disease could have come from the water, the owner of the building hired civil engineer and medical investigator George Soper to track down the cause. He discovered the other families who had fallen ill and then came across the common denominator: a heavy-set, 40-ish, unmarried Irish cook who had worked at each household.

Although she had moved on with no forwarding address, Soper quickly tracked Mary down. She did not react well to the accusation that she might have been a carrier. As Soper wrote, "I had my first talk with Mary in the kitchen of this house ... I was as diplomatic as possible, but I had to say I suspected her of making people sick and that I wanted specimens of her urine, feces and blood. It did not take Mary long to react to this suggestion. She seized a carving fork and advanced in my direction. I passed rapidly down the long narrow hall, through the tall iron gate ... and so to the sidewalk. I felt rather lucky to escape."

The New York City Health Department took over, chasing and arresting her in 1907 and placing her in quarantine. During interviews in the hospital she revealed that she rarely washed her hands while cooking. Salmonella is passed on through fecal contamination, and tests showed the bacteria existed in her gall bladder, proving that she was, indeed the carrier. She steadfastly refused to acknowledge her role and was only released in 1910 when she promised she would never work as a cook again.

That didn't last. Mary changed her name and started cooking again. When a typhoid fever epidemic broke out at Sloane Hospital for Women in 1915, investigators linked the illnesses (and two deaths) to Mary. She fled, but was captured, arrested and once again sentenced to quarantine. She lived most of her life in solitude, finally dying in 1938.

'Banished like a leper'

Although she ran from investigators, changed her identify and brandished weapons at her accusers, Mallon was never tried for breaking any laws, and yet she was locked up for decades under New York's public health statutes. She remained belligerent about this point and said she was being persecuted. She had never been sick, so how could she have been making other people sick? As she said during her first quarantine, "I never had typhoid in my life, and have always been healthy. Why should I be banished like a leper and compelled to live in solitary confinement with only a dog for a companion?"

Over the years Mary's legend has grown, linking her to hundreds if not thousands of cases of typhoid fever. The true number may never be known, but it's most likely much lower. Only 51 cases, including three fatalities, have been directly linked to her.

But Mary is still being studied today, albeit indirectly. This summer, microbiologists from Stanford University and the University of California at San Francisco unlocked how Mary could have infected so many people while remaining asymptomatic herself. They found that bacteria rely upon cells that in turn rely upon a particular protein. In tests with mice, they found that the animals with low levels of that protein remained infected with the bacteria without getting sick. The exact mechanisms are yet unknown, but this is one step closer to controlling future salmonella outbreaks. "If we can figure out what that is, it could lead to some great anti-salmonella therapeutics with relatively fewer side effects," lead author Denise Monack from the Stanford University School of Medicine said a press release recently.  

All of this is too late to help Mallon or the people she endangered, but who knows? Perhaps one day it could help prevent the next Typhoid Mary from taking an unintended toll.

For more on Typhoid Mary, you might want to check out the invaluable "Typhoid Mary: Captive to the Public's Health" by Judith Walzer Leavitt or "Typhoid Mary: An Urban Historical" by TV chef and traveler Anthony Bourdain.

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