15. The Broad Street cholera epidemic of 1854
During the third cholera pandemic an outbreak of the disease occurred in London. At the time, the medical community broadly agreed that cholera was carried in the air, in particles called miasmata. During the London outbreak, physician John Snow noted a concentration of cases reported in a community in London’s Soho district. Using a dot map, Snow established a circle of cases in an area served by a single water pump, from which the residents extracted their drinking water. The water was drawn from the River Thames. Snow postulated the water was the source of the disease, and lobbied the city to shut down the pump by removing its handle.
As Snow wrote, “The result of the inquiry then was, that there had been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump-well”. Snow’s efforts led to the birth of the science of epidemiology, and created the double-blind experiment, though the latter was a happy accident of his method of research. It was the breakthrough against cholera, up to then one of the world’s most feared illnesses. The proof that cholera was spread by contaminated water rather than “bad air” changed science, medicine, and public health services in cities around the globe, though some more swiftly than others.