English obstetrician John Snow seems as important as the similarly-named Game of Thrones hero for his role in persuading modern medicine of the germ theory of disease. During the 1854 outbreak of cholera in London, Snow convinced authorities and critics that the disease spread from a contaminated water pump on Broad Street, leading to the now-legendary infographic map above showing the incidences of cholera clustered around the pump.

Snow’s persistence resulted in the removal of the handle from the Broad Street pump and has been credited with ending an epidemic that claimed 500 lives. The Broad Street pump map has become “an enduring feature of the folklore of public health and epidemiology," write the authors of an article published in The Lancet. They also point out that, contrary to popular retellings, the “map did not give rise to the insight” that the pump and its germ-covered handle caused the outbreak. “Rather it tended to confirm theories already held by the various investigators.

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Snow and deadly cholera outbreaks in the crowded European cities of the early 19th century is online at the John Snow Archive and Research Companion.

Germ theory had a long, distinguished history already, and Snow and his contemporaries made sound, evidence-based arguments for it.
Germ theory had a long, distinguished history already, and Snow and his contemporaries made sound, evidence-based arguments for it. - Snow himself published a pamphlet in 1849 called “On the Mode of Communication of Cholera” in which he argued that “cholera is communicated by the evacuations from the alimentary canal.” As he reminded readers of The Edinburgh Medical Journal in an 1856 letter, in that same year, “Dr William Budd published a pamphlet ‘On Malignant Cholera’ in which he expressed views similar to my own.”