Causality

Question 1

Historical theories on disease causation

Answer 1

• demons: placation, exorcism, transference

- divine wrath: placation

Question 2

Metaphysical medicine

Answer 2

Disease due to occult forces beyond control, but not necessarily due to a supreme being or demonic forces

• stars, earthquakes, flood, moon, comets
• name of influenza
• allowed for disease to be measured against observable events

Question 3

Natural law

Answer 3

Disease was the result of the derangement of the 4 body humours and the 4 elements

• heat, cold, moisture, dryness
• earth, air, water, fire

Question 4

Contagion

Answer 4

Disease caused by small seeds or animacula

- aka: germ theory

Question 5

How did germ theory gain support?

Answer 5

• vaccination and apparent efficiacy
• basic research on disease pathogenesis (work done by pathologists)
• observations of naturally occurring disease in populations (epidemiology)

Question 6

Edwin Jenner

Answer 6

Developed smallpox vaccine from hand lesions of a milk maid

Question 7

Puerpural fever mortality

Answer 7

Studied by Dr. Ignaz Semmelweiss

• puerpural fever high in hospitals due to poor sanitary conditions
• controlled with aseptic technique, hygiene, antibiotics
• used observational data to explain risk factors for death from puerpural fever

Question 8

Karl Mayrhofer

Answer 8

1865, isolated microorganisms in tissues and secretions of women with puerperal fever, validating Semmelweis’ theory of contagion

Question 9

Jacob Henle

Answer 9

1840, infectious disease was caused and conveyed by invisible forms of life

Question 10

Louis Pasteur

Answer 10

1857, investigations on fermentation

- argued against theory of spontaneous generation

Question 11

Robert Koch

Answer 11

1876, published full life history of anthrax

- mentor was Jacob Henle

Question 12

Henle-Koch Postulates

Answer 12

An organism is causal if:

• it is present in all cases of disease
• it does not occur as a fortuitous or non-pathogenic parasite
• is isolated in pure culture from a case
• organism can be repeatedly passaged, and induces the same disease in other animals

Question 13

Problems with Koch’s postulates

Answer 13

• multiple etiologic factors
• multiple effects of a single cause
• asymptomatic carriers (cholera)
• non agent factors such as age
• immunologic processes as cause of disease
• host-agent, host-environment interactions
• noninfectious causes of disease

Question 14

Surgeon general’s criteria

Answer 14

• consistency
• strength of association
• specificity of outcome, time, place, population
• temporality
• coherence

Question 15

Hills criteria

Answer 15

Surgeon general criteria plus:

• dose response relationship
• plausible biologic mechanism
• experimental evidence to compliment

Question 16

Surgeon and hill criteria acknowledged that ____

Answer 16

Clinically healthy individuals frequently tolerate pathogens well

• accommodated non-infectious factors
• mandated temporal sequence
• dose response relationship adds credibility

Question 17

Required proof of _____

Answer 17

Association (statistical significance) between hypothesized causal factor and the disease

• comparing frequency of disease in different groups
• facilitate identifying factors associated with disease

Question 18

Does a statistically significant association prove causality in itself?

Answer 18

No, must use judgement, biological reasoning