John Snow and Cholera

Question 1

Population of interest

Answer 1

• # of households receiving ‘mixed’ water supplies (Broad St. pump where different companies water source mix)

Question 2

Exposure of interest

Answer 2

• Water received from Southwork company, known to be the contaminated water

Question 3

Exposed and Unexposed Groups

Answer 3

• Households receiving from Lambeth: unexposed

* Households receiving from Southfork: exposed

Question 4

Outcome of Interest

Answer 4

• Death due to cholera

Question 5

Incidence Rate Calculation

Answer 5

• # of outcomes = # of deaths
• not able to determine # of non-fatal attacks
• size of population is in terms of households at risk

Question 6

Plausibility of Theories

Answer 6

o	Communicability: Highly Likely
o	Mouth and Anus: Highly Likely
o	Rapid reproduction: Speculative
        -not everyone who drinks mixed water from Southwork acquires disease
         -duration varies in pop. size
o	Intestinal manipulation: Highly likely

Question 7

Agree or Disagree with the following statement:
“The pump handle was removed, and
the plague was [halted]” on September 8th.”

Answer 7

DISAGREE:

-decline in incidence rate prior to pump being removed

Question 8

To what extent do you think the cause of the outbreak was finally established?

Answer 8

HIGHLY LIKELY:

• Plausible sources of contamination
• Water contained impurities of possible organic origin
• Most of the cases could be traced back to the pump, cases absent from several institutions in the area that did not use the pump (aka Brewery)