John Snow and the Broad Street cholera outbreak

Proving a theory

John Snow, an anaesthetist, speculated that cholera was spread by contaminated water, an idea which was not accepted by his peers or local authorities.

The dominant theory at the time was that cholera was spread by pollution or 'bad air'. The previous year had seen outbreaks of cholera in London, Gateshead and Newcastle that killed over 10,000 people.

In 1854, another epidemic hit London, with Southwark and Lambeth the worst affected. Soho only suffered a few cases, until a violent and sudden outbreak emerged on 31 August 1854. 3 days later, 127 people living around Broad Street in Soho died and the death rate continued to grow.

Snow used the outbreak to attempt to prove his theory about the spread of cholera by linking the Soho outbreak to a single source of water. His research led him to a water pump on Broad Street. While the parish's Board of Guardians was sceptical that the pump had been the source of the infection, they agreed to remove the pump handle as an experiment and the spread of cholera was stalled.

Snow's theories were still not accepted, however. The Reverend Henry Whitehead, the local parish vicar, undertook his own report, but his findings confirmed Snow's theory and helped to isolate the cause of the infection. A child had been taken ill with cholera and its nappies had been cleaned in water that was subsequently tipped into a cesspool close to the Broad Street well.

Later developments

German doctor Robert Koch proved that bacteria could cause disease and identified the bacteria that caused cholera. Building on the germ theories of Louis Pasteur, Koch developed new methodology to test whether a particular micro-organism (Bacillus anthracis) was the cause of anthrax.

In 1876, he extracted the bacterium from sheep that had died of anthrax, grew the bacterium and then injected a mouse with it. The mouse developed the disease. Koch's team later identified the bacteria that caused tuberculosis in 1882 and cholera in 1883.

Other researchers adopted his methods and were able to identify the bacteria that caused typhus (1880), tetanus (1884) and the plague (1894).


UCLA, Dept of Epidemiology.
Broad Street pump outbreak.
UCLA; nd.

Science Museum Group.
Robert Koch (1843–1910).
Science Museum Group; nd.