How An Honest Scientist Inadvertently Helped A Municipal Cover-Up

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In Chicago, in 1902, an outbreak of typhoid was killing people and no one knew why. One courageous scientist waded into the middle of the epidemic and figured it out. Or so she thought. Years later, she discovered her efforts had enabled a cover-up of the real problem.


The scientist was Alice Hamilton, a brilliant bacteriologist living and working in Chicago at the turn of the 20th Century. Hamilton was recognized by her peers not only as a gifted scientist (she would later become the first woman appointed to the faculty at Harvard Medical School), but an outspoken advocate for human rights. When an epidemic of typhoid broke out in a poor neighborhood near where she lived, she was a natural choice to identify the source of the outbreak.

When Hamilton toured the neighborhood, she found illegal outhouses behind the tenement houses. The privies were built and maintained by tenants, who couldn’t make do with the tiny, over-loaded, and badly maintained bathrooms in their own buildings. The makeshift latrines were ridden with flies. But so, too, were the tenants’ kitchens. Unlike the rich, the poor had few screens on their windows, so Hamilton figured that it wasn’t a long trip, for a fly, from an outhouse to a kitchen.

Hamilton’s investigation is still held up as an example of how public safety research should be conducted. She took flies from both the privies and kitchens, put them in broth, and cultured the broth. She discovered that flies from the outhouses were carrying typhoid bacteria. So were flies from the kitchens. Hamilton recommended that tenants scrub their kitchens clean, cover their food, and wash their hands religiously. Public health reports proclaimed “The Guilt Of The ‘Typhoid Fly’” had been “Scientifically Established.” The events triggered an increase in public support for laws that required landlords to supply adequate bathrooms for their tenants, and keep them clean and in working order.

The problem was: The flies had not caused the typhoid outbreak.

While the conditions of the tenement housing were certainly deplorable, the problem actually laid beneath the housing. There, a sewer pipe had broken and leaked into a water pipe. Hamilton was not aware of this when she did her experiments. Had this come to light, it would have made the Board of Health look extremely bad, and so, when Hamilton established a link between flies and typhoid, the city opted to point the finger at the landlords and flies.

When she learned the true cause of the typhoid outbreak, Hamilton, to her credit, loudly proclaimed that her most famous experiment had provided the wrong conclusion. But for the rest of her life, she was often introduced as the person who had stopped the typhoid epidemic by stopping the flies.

Image: Thomas Bresson




A fine example of “correlation does not imply causation.”