London's deadliest cholera outbreak was traced to a single street pump.
In 1854 cholera killed hundreds in Soho within days. Most experts blamed foul air. The physician John Snow asked a simpler question, where did the dead get their water, and the answer pointed to one pump on Broad Street. His detective work is often called the founding moment of epidemiology.
In mid-nineteenth-century London, the leading explanation for cholera was miasma: disease was thought to rise as a poisonous vapour from rotting matter. Soho certainly smelled bad. The sewers had not reached it, many cellars sat above overflowing cesspools, and waste was being tipped into the Thames. John Snow suspected something else, that cholera spread through something people swallowed, above all contaminated water. He had argued this since 1849, long before germs were understood.
On 31 August 1854 the outbreak exploded around Broad Street. In three days, 127 people nearby died, and by the end about 420 were dead. Helped by a local curate, Henry Whitehead, Snow questioned residents and found that deaths clustered tightly around one public pump. Even the exceptions fitted: some victims lived nearer other pumps but preferred Broad Street's water, while workers at a nearby brewery, who drank their daily beer allowance instead, escaped. He later plotted the deaths on a now famous dot map.
On 7 September Snow put his evidence to the parish authorities, and the pump handle was removed the next day. The popular version says this ended the outbreak. Snow himself was more cautious: cases were already falling, partly because most residents had fled. The well was later found to lie about a metre from a leaking cesspit, into which water used to wash a sick baby's nappies had drained.
Snow's strongest evidence came from a wider comparison. Two water companies served the same streets, one drawing sewage-laden water from the Thames and the other taking cleaner water further upstream. Households supplied by the first had a cholera death rate about 14 times higher, across some 300,000 people who had not chosen their supplier. Officials rejected his theory at the time and even put the handle back. A pub near the site now carries his name.
Source: Wikipedia — 1854 Broad Street cholera outbreak · Text summarised from Wikipedia (CC BY-SA 4.0)
