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

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

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

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

5. Ecological Study Key data in Figure 1.13 (p. 24) Columns in TableColumns in Table Sub-district (neighborhood)Sub-district (neighborhood) Population (denominator)Population (denominator) Cholera deaths 1853 (numerator)Cholera deaths 1853 (numerator) Mortality per 100,000 = numerator / denominator × 100,000Mortality per 100,000 = numerator / denominator × 100,000 Water companies serving neigborhoodWater companies serving neigborhood Example of rate calculationExample of rate calculation Rate St. Saviour = 45 / 19,709 × 100,000 = 227Rate St. Saviour = 45 / 19,709 × 100,000 = 227 Rate Christchurch = 7 / 16,022 × 100,000 = 43Rate Christchurch = 7 / 16,022 × 100,000 = 43 Water sourceWater source St. Saviour – Southwark and Vauxhall Water OnlySt. Saviour – Southwark and Vauxhall Water Only Christchurch – Lambeth and Southwark and Vauxhall Water (both companies serving neighborhood) 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 sourceData by household water source Rate per 10,000Rate per 10,000 Rate Southwark & Vauxhall = 1263 / 40,046 × 10,000 = 315Rate Southwark & Vauxhall = 1263 / 40,046 × 10,000 = 315 Rate Lambeth = 98 / 26107 × 10,000 = 37.5Rate Lambeth = 98 / 26107 × 10,000 = 37.5

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

8. Fig 1.14 (p. 25)

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