Snow, John

In 1854, John Snow was a well-regarded London anesthesiologist, tending to Queen Victoria, among others. He was born in 1813 of humble stock, but through education and intellectual perseverance—he obtained his M.D. degree in 1844—was able to rise to a position of scientific prominence. Snow became interested in the emerging field of epidemiology , especially as it applied to cholera, a disease of unknown cause (attributed thirty years later by Dr. Robert Koch to Vibrio cholerae ). Two population-based studies—both occurring in 1854—established Snow's reputation, and focused scientific attention away from the fallacious notion of airborne transmission towards the role of contaminated water in the spread of cholera.

Snow's first study occurred after the government had mandated that water companies along the polluted Thames River should move their inlets upstream where the quality of water was better. One company moved its intake pipes in 1852 but still maintained the same local water distribution system. A second company kept its intakes in place (but finally moved in 1855), providing contaminated water to portions of the same area as the first company. When cholera next arrived in London in 1853 and 1854, Snow was able to compare cholera among households according to water source. The populations were very similar—consumers of the two water companies lived side by side. Using existing mortality data, Snow was able to measure the impact the two companies had on cholera, thereby linking water source and quality to the disease.

His second study took place in 1854 near his home in the Soho region of London. It followed what he described as: "The most terrible outbreak of cholera which ever occurred in this kingdom." With skillful assembling of data, analysis, and use of maps, he identified a single water pump on Broad Street as the likely source, suggesting that the pump water was contaminated with an unseen microbial agent. Water pumps, at that time, were hand-operated pumps with spigots—people pumped their water into buckets to be carried home. There was no "running water," as we know it, in people's homes. Snow recommended to local politicians that the pump handle be removed, which was done during the declining days of the outbreak. For this, he is remembered as a public health hero.

John Snow died in 1858 at age forty-five. During his short life, he became a pioneer in both anesthesiology and epidemiology, and clarified the role of water, rather than air, in cholera transmission.

Ralph R. Frerichs

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