that's a fascinating historical case, first time I learned of it. Do we know how exactly Mary spread the disease? Was it unwashed hands or saliva or her breath? How is typhoid transmitted exactly?
She was a cook who did not wash her hands thoroughly after defecating. Salmonella typhi bacteria causes typhoid and is excreted in feces. She transferred it into cold food--e.g. salads, peach ice cream--that she prepared (cooking kills the bacteria). The doctors of the time theorized that the Salmonella typhi had colonized her gallbladder. There were many asymptomatic carriers detected at the time but few if any persisted as cooks or preparing food once they had been warned.
