ResearchBlogging.orgBetter Know An Epidemiologist/History of Epidemiology is an ongoing feature where Mr Epidemiology pays tribute to people and studies that have set the stage for his generation of epidemiologists. All of the articles are listed here.

Gaetan Dugas, Air Canada flight attendant and one of the first diagnosed cases of HIV

EDIT 10/01/12: I had indicated (incorrectly) that Typhoid Fever was a viral disease. It is in fact due to a bacterium instead. Thanks to Mike the Mad Biologist for pointing that out!

EDIT 10/01/12: As Brett Keller points out in the comments, Gaetan Dugas was not Patient Zero for HIV. While he contributed to the spread of the virus, he wasn’t the first known case of it, and so the label of Patient Zero is unfairly applied to him.

Patient Zero is a common infectious disease epidemiology term. It refers to the first known case of the disease of interest, and is useful when tracking disease outbreaks. Knowing where the disease starts allows us to track not only the spread of the disease, but also how it spreads – through water, air, person-to-person contact etc.

I heard an absolutely phenomenal podcast through WNYC’s RadioLab podcast about Patient Zero, and that formed the inspiration for this post. I highly recommend listening to it when you have a chance – either through iTunes, on their website. They cover several different “Patient Zero’s,” including Typhoid Mary and Gaetan Dugas (pictured above).

Today, I’ll be talking about Typhoid Mary. To listen exclusively to the Typhoid Mary segment of the RadioLab podcast, click here.

Click the image to go to the RadioLab podcast about Patient Zero.

A historical poster cautioning people against acting like Typhoid Mary (pic goes to Wikipedia article)

Mary Mallon was born September 23rd, 1869, and is of interest to Epidemiologists as she was the first known asymptomatic case of typhoid fever. Typhoid fever is estimated to affect between 16 – 33 million people annually. Fatalities from typhoid drop to less than 1% if treated quickly with oral rehydration therapy. However, when untreated, death occurs in 10% – 30% of those infected (for more information about the disease itself, check out this excellent Infection Landscapes post). The name is derived from the Greek word “typhus” or stupor, as infected individuals suffer from malaise and a high fever. It is spread through the feces of contaminated individuals, generally after those feces come into contact with either food or water. The typhoid bacteria can be destroyed by cooking food thoroughly and boiling water before drinking it. Washing hands and cleaning dishes also prevents transmission of the bacteria.

Now back to Mary Mallon. Mary was born in Ireland, and moved to the US in 1884. She was a cook, and in 1900, she was working for a family in Mamaroneck, NY. Soon after she started there however, the residents developed typhoid fever. She moved to Manhattan in 1901, and worked for a new family. Sure enough, this family developed typhoid fever also. After this, she moved to Oyster Bay, Long Island, infecting a third family.

George Soper, a typhoid researcher, found Mary was the link between the first three families, and approached her to obtain a stool and blood sample. As you can imagine, this conversation didn’t go over well – not only was there no prior evidence for asymptomatic typhoid fever, this isn’t exactly something you can ask someone for after accusing them of making people sick (or at any time really). Adding to this was the anti-Irish and anti-immigrant sentiment of the time, feeding Mary’s view that she was being unfairly persecuted.

Soper published his findings as a case-report in JAMA, charmingly entitled “The work of a chronic typhoid germ distributor.” Mary chased him away multiple times, wielding kitchen utensils as weapons. Soper wrote about his experiences in a 1939 article in the Bulletin of the NY Academy of Medicine.

Dr Sara Baker was sent to Mary Mallon’s house, as it was felt that a female doctor may be more persuasive than a male. After being refused again, Dr Baker went to Mary’s workplace with police officers, and had her arrested. Mary was tested, deemed to be a carrier, and placed in isolation on North Brother Island.

Part of the New York American article of June 20, 1909, which first identified Mary Mallon as "Typhoid Mary." Photo Credit: New York County Clerk Archives via Planck's Constant (click pic to go to their site)

Mary was kept in isolation from 1907 to 1910. However, in 1910 the New York State Commissioner of Health decided that disease carriers should no longer be kept in isolation, and so Mary was allowed to return to work, provided that she did not work as a cook. She left, and started working as a laundress, washing clothes. However, this paid less, so she adopted the name Mary Brown, and returned to life as a cook. She got a job working at New York’s Sloane Hospital for women, and is suspected to have infected a further 25 people with typhoid fever before being caught by the health authorities again in 1915. She was sent back to isolation, and lived out the rest of her days there. She passed away on November 11th, 1938 from pneumonia.

But wait. Something doesn’t sit right here.

The bacteria can be destroyed by washing hands, using clean utensils, and above all, by cooking food thoroughly. So how did Mary Mallon transmit the disease? Assuming she kept her hands clean, cooked food thoroughly and cleaned plates, she shouldn’t have passed it on right?

For the answer, you’ll have to listen to RadioLab’s podcast. And trust me, it’s worth it.

Special thanks for Kim F and Jessica S for helping me prepare this article!


SOPER, G. (1907). THE WORK OF A CHRONIC TYPHOID GERM DISTRIBUTOR. JAMA: The Journal of the American Medical Association, XLVIII (24), 2019-2022 DOI: 10.1001/jama.1907.25220500025002d

Soper GA (1939). The Curious Career of Typhoid Mary. Bulletin of the New York Academy of Medicine, 15 (10), 698-712 PMID: 19312127