On March 27, 1915, "Typhoid Mary" Mallon was the first person in the United States ever to be identified as an asymptomatic carrier of the pathogen. An immigrant from Ireland, she was employed as a cook for wealthy families throughout New York City. As typhoid fever was associated with poverty, a mystery began to develop, because health officials couldn't understand why affluent people were coming down with the disease. It was eventually found that Mary Mallon was the link, as she was the cook for all of the families who had come down with the illness. She was placed into quarantine and released after three years. As a condition of her release, she had to promise that she wouldn't work as a cook anymore, but she continued to do so anyway. After typhoid fever broke out at Sloan Maternity Hospital in New York, Mary was discovered to be the hospital's cook, even though she had been using a different name. She was again sent into isolated into quarantine, but this time for 23 years, where she eventually died. Unfortunately, Mary lived in a time when microbiology was still in a state of relative infancy. Because she had no symptoms, she couldn't understand why people were telling her that she was sick. Without understanding the nature of microscopic organisms, she was also unable to grasp the purpose of hand-washing.