The Broad Street cholera outbreak was a severe outbreak of cholera that occurred near Broad Street in the Soho district of London, England in 1854. This outbreak is best known for the physician John Snow's study of the outbreak and his discovery that contaminated water, not air, spread cholera. This discovery came to influence public health and the construction of improved sanitation facilities beginning in the 19th century. Later, the term "focus of infection" would be used to describe places like the Broad Street pump in which conditions are good for transmission of an infection. In the mid-19th century, the Soho district of London had a serious problem with filth due to the large influx of people and a lack of proper sanitary services: the London sewer system had not reached Soho. Many cellars (basements) had cesspools underneath their floorboards. Since the cesspools were overrunning, the London government decided to dump the waste into the River Thames. That specific action contaminated the water supply, leading to a cholera outbreak. On 31 August 1854, after several other outbreaks had occurred elsewhere in the city, a major outbreak of cholera reached Soho. John Snow, the physician who eventually linked the outbreak to contaminated water, later called it "the most terrible outbreak of cholera which ever occurred in this kingdom."[1]

Over the next three days, 127 people on or near Broad Street died. In the next week, three quarters of the residents had fled the area. By 10 September, 500 people had died and the mortality rate was 12.8 percent in some parts of the city. By the end of the outbreak, 616 people had died.Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution or a noxious form of "bad air". The germ theory was not established at this point (as Louis Pasteur would