Monkeypox, COVID, and polio: These three very different diseases have been dominating news cycles recently, but they share at least one common characteristic: some people can become infected — and in turn infect others — while showing no symptoms.
In 1883, the famous bacteriologist Friedrich Loeffler (1852–1915) recognized that an individual's asymptomatic carriage of bacteria could lead to diphtheria in others. Now, as then, asymptomatically infected people present a conundrum: How do you fight the spread of a disease when you can't identify some of the people who are spreading it?
"Typhoid Mary" is perhaps the quintessential example of asymptomatic transmission of infections leading to illness and death. At the turn of the 20th century, young Mary Mallon emigrated from Ireland to New York City, where she soon became a cook for wealthy Manhattan families.
George Soper, a sanitary engineer, was hired by a stricken family to investigate. After epidemiologic study, he suspected that Mary was a carrier of Salmonella typhi,the bacterial cause of typhoid fever. He persuaded the NY Department of Health to test her — against her will — for infection. After her stool was found to test positive for Salmonella, Mary was forcibly moved to North Brother Island, where she remained largely isolated from others for the next 2 years.
