On this day in 1869 in County Tyrone, Ireland, a baby girl by the name of Mary was born. Certainly, there’s nothing unusual in that. Very little is known of the formative years of young Mary Mallon, but at the age of 15 she became a part of the Irish diaspora headed for the United States and emigrated to New York. For a time she lived with her aunt and uncle before beginning to earn a living as a cook for well to do New Yorker families.

Mary found it difficult to hold down a job. There’s nothing to suggest that her culinary skills weren’t up to scratch, but it seemed she was quite unlucky in her employers. Between 1900 and 1907 she worked for seven different New York families. The first, in Mamaroneck, was ravaged by Typhoid within two weeks of her employment beginning. The next year, at a job in Manhattan, the family developed fever and diarrhoea; one of her coworkers even died. At her next position, all bar one of the family became severely ill. The same thing happened in Oyster Bay, Long Island, in 1906 with ten of eleven family members becoming seriously ill.

It was around this time that one of the families hired an investigator to try to pin down how it was they caught typhoid. George Soper published his results in the Journal of the American Medical Association in June, 1907. He noted, “It was found that the family changed cooks on August 4. This was about three weeks before the typhoid epidemic broke out. She remained in the family only a short time, leaving about three weeks after the outbreak occurred. The cook was described as an Irish woman about 40 years of age, tall, heavy, single. She seemed to be in perfect health.”

Soper had discovered that an Irish cook who fit the same description was involved in each of the outbreaks, though he couldn’t track her down as she never left a forwarding address. Before long, however, another outbreak of typhoid soon occurred and who else did he find at the centre of it than poor Mary Mallon.

I can’t tell you if Mary had any idea that she had been spreading typhoid wherever she went, but when confronted by Soper she refused to cooperate. He had wanted urine and faecal samples for analysis but instead Mary simply locked herself in the bathroom until he left.

Later that year, though, Mary was arrested after an intervention by the New York City Health Department. Though she had committed no crime, Mary was deprived of her liberty, firstly in hospital and then in jail where the urine and stool samples were finally obtained that proved she was a carrier of typhoid. Unusually, Mary had no symptoms of the disease, she was an asymptomatic carrier, the first ever noted. Given her good health, Mary never accepted that she was infected and refused to give up her career as a cook, though she admitted her hygiene was poor.

Mary was subsequently held in isolation until 1910 at which point she promised that she was “…prepared to change her occupation (that of a cook), and would give assurance by affidavit that she would, upon her release, take such hygienic precautions as would protect those with whom she came in contact, from infection.” She was released shortly after.

During her imprisonment, though, Mary had become notorious. In 1908 she was first described as Typhoid Mary, and then again in 1912 in a textbook on typhoid. The name stuck. More than a century later almost no one has heard of Mary Mallon, but everyone knows Typhoid Mary.

Upon release Mary worked as a laundress, but it didn’t pay as well as being a cook and so she changed her name to Mary Brown and began working as a cook again despite being prohibited from doing so. For three years she spread typhoid wherever she worked leading to multiple outbreaks. Soper suspected that Mary was, again, wreaking her havoc but she never stayed in the same job for long and so he failed to track her down.

Mary was finally caught in 1915 after causing another major outbreak at Sloane Hospital for Women in which two people died. On March 27th of that year she was again confined to isolation in Riverside Hospital, North Brother Island, New York; and that is where she stayed until she died of pneumonia 23 years later.

Mary never accepted that she had been spreading the disease around New York, this made it particularly difficult to pin down the outcomes of her actions. She is thought to be responsible for as many as 50 deaths, though.

The case of Mary Mallon is a curious one indeed. Today, at least in the west, typhoid rarely leads to serious illness as it can be cured by a course of antibiotics. But a century ago the combination of an unwitting public and one woman’s stubborn streak led to dozens of preventable deaths including those of several children. Mary was the first asymptomatic case of typhoid known to science and in that sphere her legacy was profound; but to the general public her name has merely become a byword for someone to avoid.