The Pump Handle That Founded Epidemiology

In late August 1854, an outbreak of cholera ripped through the Soho district of London. By September 10, more than 500 people in a few streets around Broad Street were dead. The dominant medical theory at the time was miasma — bad air rising from rotting matter — and that was what most physicians and the Board of Health were investigating.

John Snow, a 41-year-old London anaesthetist who had attended Queen Victoria for chloroform during childbirth, had argued for years that cholera was waterborne. He went to Soho with a notebook. Working from the register of deaths, and helped by a local curate named Henry Whitehead who knew the neighbourhood, Snow plotted each cholera death on a street map. Almost every dot clustered around one fixture: a public water pump at the corner of Broad Street and Cambridge Street.

Two anomalies tightened the case. The Lion Brewery on Broad Street, a few doors from the pump, had 70 employees and not a single cholera death — the men drank beer in lieu of pump water, and the brewing process had boiled it. A poorhouse with its own well, surrounded by deaths, was almost untouched. Snow brought his data to the local Board of Guardians on September 7. The next day they removed the pump's handle.

The outbreak was already easing — much of Soho had fled — but the map, published in 1855, was the first epidemiological case made by drawing a disease onto geography. The contamination, traced afterwards by Whitehead, came from a cesspit roughly a metre from the well. An infant nearby had died of a cholera-like illness, and the wash water from her soiled napkins had drained into the cesspit, which seeped into the supply.

Snow died in 1858 still in the minority on cholera. Within twenty years his reading of the data was the medical consensus.