John Snow and the 1854 Cholera Outbreak

• Cholera is caused by the Vibrio cholerae bacterium infecting the small intestine.
• Watery diarrhea and vomiting are major symptoms, potentially leading to dehydration and death.
• Fecal contamination of drinking water or food is the primary transmission method.
• Infected individuals, even without apparent symptoms, can transmit the disease.

Historical Context of the 1854 Cholera Outbreak

• By the mid-19th century, Soho, London, was unsanitary with animal waste, slaughterhouses, and poor sewage systems
• Overcrowded tenements had cesspools under floorboards, creating a health hazard
• The summer of 1854 saw an explosion of cholera in this environment

Dr. John Snow's Investigation

• Cholera was initially believed to be airborne when it hit England in 1831.
• Dr. John Snow (1813–1858) was an anesthesiologist and epidemiology pioneer.
• Snow proposed cholera spread through contaminated water, which was not widely accepted.
• Cholera outbreaks were common and deadly, with 10,675 deaths in three English cities in 1853.
• Southwark and Lambeth were initially hit hardest in the 1854 London epidemic.
• A severe outbreak began in Soho on August 31, 1854, causing 127 deaths in three days.
• Three-quarters of residents fled, and fatalities reached 500 by September 10th.
• Snow's intervention was crucial in preventing even more deaths.

Scientific Methods in Snow's Research

• Dr. Snow's research aimed to explain the cholera outbreak and prevent future occurrences
• Snow believed cholera spread through sewage-tainted water, like a poison.

Use of Scientific Methods

• Interviews with victims' families helped gather data
• Spot mapping geographically showed the distribution of cases
• The spot map revealed the Broad Street pump as the outbreak's epicenter.
• Water sample analysis showed "cholera bacteria" in the Broad Street pump water
• An experiment involved removing the Broad Street pump handle, slowing the cholera spread.
• An epidemic curve showed the number of cholera deaths declining rapidly.
• Cholera's short incubation period (1-3 days) helped identify the outbreak's source.

Unexplained Inconsistencies

• The death toll at the end of September was 616 people
• Some deaths could not be directly linked to the Broad Street pump.
• A widow in Hampstead died of cholera after receiving water from the Broad Street pump.
• Workers at a brewery who drank beer instead of water had no fatalities.
• 530 inmates of the Poland Street Workhouse close to the pump, but with its own well, only five people contracted cholera
• An army officer contracted cholera after dining at a restaurant using Broad Street well water

Confirmation and Conclusion

• A Board of Health report dismissed Snow's theory initially.
• Reverend Henry Whitehead's investigation supported Snow's findings, disproving divine intervention
• Contaminated diapers washed into a leaking cesspool near the Broad Street well likely caused the outbreak.
• A report published a year later revealed ongoing poor conditions in Soho.

Snow's Contributions

• Proposed a new hypothesis for cholera transmission
• Evaluated his hypothesis by comparing groups from different areas
• Used spot mapping to visualize the concentration of cases
• Showed a correlation between the Broad Street well and contracting cholera
• Advocated for pump handle removal, an intervention which prevented more cases.

An examination of the 1854 Cholera outbreak in London and John Snow's investigation. The waterborne theory of disease transmission emerged from Snow's work. Overcrowding and poor sanitation worsened the spread of cholera.