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John Snow's Epidemic Insights and Methods

Explore the life and work of John Snow, the pioneering Victorian surgeon and epidemiologist. Discover his groundbreaking theories on disease transmission, exemplified by his waterborne cholera theory and innovative epidemiologic methods. From ecological and cohort studies to case-control analysis, Snow's legacy continues to shape modern epidemiology.

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John Snow's Epidemic Insights and Methods

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  1. John Snow Highlights from pp. 19 – 26 in Gerstman (2003)

  2. Who was John Snow? • Victorian surgeon / anesthesiologist • Realized his obligation went beyond treating individual patients • Quintessential hero of epidemiology • Insightful theory of disease • Impressive methods of studies

  3. Snow’s Waterborne Theory • Based his theory on two facts • Early symptoms restricted to GI tract • Epidemics followed commerce and armies • Theorized cholera agent is: • swallowed • passed from person-to-person • multiplies within the host

  4. Snow’s Epidemiologic Methods • Ecological study = compared rates by region • Cohort study = compared rates by water source • Case-control study = compared water source (exposure) in cases and non-cases

  5. Ecological StudyKey data in Figure 1.13 (p. 24) • Columns in Table • Sub-district (neighborhood) • Population (denominator) • Cholera deaths 1853 (numerator) • Mortality per 100,000 = numerator / denominator × 100,000 • Water companies serving neigborhood • Example of rate calculation • Rate St. Saviour = 45 / 19,709 × 100,000 = 227 • Rate Christchurch = 7 / 16,022 × 100,000 = 43 • Water source • St. Saviour – Southwark and Vauxhall Water Only • Christchurch – Lambeth and Southwark and Vauxhall Water (both companies serving neighborhood)

  6. Cohort Study Key data in Table 1.7 (p. 25) • Data by household water source • Rate per 10,000 • Rate Southwark & Vauxhall = 1263 / 40,046 × 10,000 = 315 • Rate Lambeth = 98 / 26107 × 10,000 = 37.5

  7. Case-Control Study • Collect data on all cases • Determine source of water for cases and non-cases (“controls”) • See text (pp. 23 – 26) for selected interviews • Also see map – Fig. 1.14 (next slide) • Conclusion: Cases more likely to use water from Broad Street Pump

  8. Fig 1.14 (p. 25)

  9. 20th Century Epidemiology(p. 26) • Shift from acute contagious disease to chronic degenerative (noninfectious) disease • E.g.s. • British Doctors Study (Long Term Effects of Smoking) • Framingham Heart Study (Risk Factors for Cardiovascular Disease)

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