Who conducted a Broad Street, London case study in 1854 to determine that cholera was linked to contaminated water?

• A. Louis Pasteur
• B. John Snow
• C. Ignaz Semmelweis
• D. Florence Nightingale

Answer: (B)

This question tests understanding of early epidemiology and how investigators established disease links by using data and real-world interventions rather than relying on vague ideas about bad air. John Snow’s Broad Street investigation in 1854 is the classic example. He mapped where cholera cases were occurring in London and found a strong cluster around the Broad Street water pump. By tracing water sources for households, he formed a persuasive link between the outbreak and the contaminated water supply, rather than air or “miasma.”

The turning point came when he showed that people who drank from that pump were more affected, and when the pump handle was removed, new cases fell. This concrete intervention—removing the source—provided practical evidence that the disease was spreading via a contaminated water supply. Snow’s approach combined careful observation, data collection, and an actionable public health measure, making it a foundational moment for epidemiology and for understanding how to control outbreaks.

Other figures you might hear about in medical history contributed in different ways: Pasteur’s germ theory work, Semmelweis’s handwashing in hospitals, and Nightingale’s sanitation reforms and statistics in nursing. They’re important, but they’re not the Broad Street cholera investigation.