1854 Broad Street cholera outbreak and John Snow's investigation

Background. London experienced a series of debilitating cholera outbreaks prior to 1854. At the time, medical professionals debated two competing theories: miasma theory, which attributed cholera to bad air, and germ theory, which suggested waterborne transmission. The 1854 Soho outbreak occurred during the worldwide 1846–1860 cholera pandemic, providing a critical case study for these theories.

Investigation. John Snow, assisted by Reverend Henry Whitehead, interviewed local residents to trace the outbreak's source. Snow identified the public water pump on Broad Street as the focus of infection. Although chemical tests did not conclusively prove danger, the spatial patterns of illness and death persuaded St James parish authorities to remove the pump handle.

Impact. Snow's work is considered foundational to modern epidemiology. His maps showed the highest incidence of cholera in areas where the closest water source was the Broad Street pump. The outbreak caused remaining upper-class families to leave Soho. The Board of Health ultimately attributed the epidemic to miasma, despite Snow's findings.