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August-September 1854Peer-reviewed · 2 sourcesWell documented

John Snow Traces Cholera to the Broad Street Pump

A London physician maps a cholera outbreak house by house, disproves airborne "bad air" as the cause, and founds modern epidemiology

On the timeline · around August-September 1854 · The Birth of Vaccination and EpidemiologyThe Birth of Vaccination and EpidemiologyModern Pandemics and Modern MedicineJohn Snow Traces Cholera to the Broad Street Pump177518001825185018751900

Quick facts

Investigator
John Snow
Location
Broad Street, Soho, London
Date
August 31 to September 7, 1854
Toll
About 500-600 deaths in the immediate outbreak
Method
Case mapping and household interviews tracing deaths to a single water pump

What happened

On August 31, 1854, a cholera outbreak began in the Soho district of London, and within ten days about 600 people had died, with roughly 500 deaths concentrated in the first ten days near Broad Street. John Snow, a London physician, rejected the dominant miasma theory that blamed foul air, and instead mapped every death by household address. The map showed deaths clustering tightly around a single water pump on Broad Street, and Snow's door-to-door interviews found that nearly all the victims had drunk water from that pump, either regularly or occasionally, while workers at a nearby brewery who drank beer instead of pump water were largely unaffected. On September 7, 1854, Snow presented his findings to local officials and persuaded them to remove the pump's handle; new cases in the area dropped sharply afterward, though the outbreak was already waning as residents fled the area.

Why it matters

Snow's map-and-interview method, tracing disease back to a single contaminated source through spatial and case-by-case data rather than theory, is the founding methodology of modern epidemiology, predating any germ-based explanation for cholera by decades. It also directly challenged and helped displace the miasma theory that had dominated medical thinking about disease transmission for centuries.

How we know

Snow published his findings and map in his own work on the mode of cholera's communication; modern epidemiological histories, including peer-reviewed retrospectives in PMC, treat this as the founding case study of the discipline based on Snow's original data and correspondence.

Sources

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John Snow Traces Cholera to the Broad Street Pump · Pandemics Through History · SourcedStory