PHPH 101

Class 4: “Evidence-based Public Health I”

• Central Question: “What is “evidence-based” public health?

• Fundamental Concepts:

– Personal/public health decisions should be based on “evidence” that certain intrinsic and extrinsic agents cause disease or influence health, and that these can be controlled to reduce disease or promote health

– The underlying theory of public health is that the distribution of health/disease in populations is not random, and that we can identify the reasons for nonrandomness

• Learning Objectives– To understand what does/does not constitute “evidence”– To understand how “evidence” is used to guide public health policy,

recommendations and action

• “I believe there is a link between vaccination and autism!”a. Strongly agreeb. Somewhat agreec. Somewhat disagreed. Strongly disagree

Clicker Question #1

Prompts for brief class discussion: Why? What’s the basis (evidence +/-) for your answer?

What sort of evidence do you think you need to answer the question?

• What is “evidence”?a. Proofb. Testimonyc. Beliefd. Datae. Facts

Clicker Question #2

Prompts to Think/Pair/Share #1:

Try to provide real-world examples of each possible answer.

Try to come up with a more precise definition

• Further prompts for TPS discussion:– Describe the “scientific method”.

– Does “evidence-based” decision making imply application of the scientific method?

– What do you think the relationship is of:

• Fundamental Concept #1– (Personal/public health decisions should be based on “evidence” that certain

factors (e.g. “agents”, “exposures”, “behaviors”) are positively/negatively (“causally?”) related to health/disease)

• to concept #2?– (The underlying theory of public health is that the distribution of health/disease in

populations is nonrandom)

The Origin of “Evidenced-based Public HealthCholera in 19th Century England

1831-1832: first modern outbreak in Britain 23,000 deaths helped to launch the sanitary reform movement

1848-1849: 250,000 cases and 53,000 deaths prompted Snow (and others) to investigate causes

• From the Greek “Miasma” = “pollution”• Disease is caused by tiny creatures (“miasmata”) that are

spontaneously generated in certain places with “vapors” or “bad air” (“malaria”)

• Decaying biological mass causes miasma (e.g. swamps; polluted rivers; battlefields; mass graves, etc.)

• Natural sources, such as volcanos, also cause miasma• Traditional responses:

– Avoid places with dank, offensive smells– Eliminate or clean-up places with foul odors

MiasmaThe Dominant Theory of Disease Causation in the

19th Century*

*Historical origin circa 400 BC, demise circa 1880 AD

• “I believe that miasma (bad smelling air) causes cholera!”a. Strongly agreeb. Somewhat agreec. Somewhat disagreed. Strongly disagree

Clicker Question #3:

Prompt: Instead of questioning the belief in a putative link between vaccination and autism, people in the mid-19th Century would have been more concerned with the following issue:

Were there any alternative possibilities?

The Competing Concept of Contagion

• Disease is caused by something unknown that spreads from person-to-person through contaminated artifacts, bodily fluids, or other “agents”

• Traditional responses:– Kill or drive off sick people– Burn the houses and belongings of the sick– Run away

Edwin Chadwick(President, General Board of Health, 1832-1848)

• Major champion of sanitary movement

• Strongly argued for government action and public support for building sewers, cleaning refuse from streets, draining swamps– Origin of public health as a government responsibility

• Ardent supporter of the “Miasma Theory”:– “All smell is, if it be intense, immediate acute disease; and

eventually we may say that, by depressing the system and rendering it susceptible to the action of other causes, all smell is disease” (emphasis added)

Prompt to Think/Pair/Share #2:• Chadwick attributed the cholera epidemics to the accumulation

of human/animal/industrial wastes in the city streets that emitted “miasmata” that the nose could readily detect by their noxious smell.

• His solution was to have laws passed requiring the clearing of streets and the building of the first public sewers to carry the “effluent” into the Thames River.

– Was this an “evidence-based” public health action• Why or why not?• Consider the quality of the “evidence”

– Was it “sufficient”– What other “evidence” might be needed

– Do you think it was effective in ending the cholera epidemics?

“Clue” to right answer: getting rid of smelly waste by dumping it into the river did notend the cholera epidemics, but actually may have worsened them.

• Quote from Steven Johnson (author of “The Ghost Map”: “Its not just that the authorities of the day (a.k.a. Chadwick) were wrong about miasma; it’s the tenacious, unquestioning way they went about being wrong”

• Introduce John Snow– Background clues:

• Physician and early anesthesiologist• Understood gases and knew that smelly ones didn’t necessarily

cause disease• Also made repeated note to “authorities” early on that it seemed a

contradiction to miasma theory that with many people sharing the same squalid living conditions and exposed to the same foul air, only some got sick. How could you explain this apparent “randomness” by miasma theory?

John Snow (1813-1858)(my hero, sob…)

Snow’s “Ghost Map”

- Brief explanation of geography, markers and symbols- Prompt for TPS #3: What’s your interpretation of the “evidence” on this map?

Other Pumps (Lambeth and Other)

Broad StreetPump

(Southwark& Vauxahall)

John Snow’s Numerical Analysis

40,046

26,107

256,423

1,263

98

1,422

315

38

56

Southwark & Vauxhall

Lambeth

Other

Water Supply N of Houses Deaths Deaths/10,000Houses

- This table shows data Snow compiled on cholera deaths by water company.

- Prompt for TPS #4: What’s your interpretation of the “evidence” in this table?

Cholera Story Wrap-up

• Removal of the Broad Street pump handle by Snow, thereby stopping the epidemic, is legend (i.e. NOT based on historical “evidence” – he persuaded the public authorities to removed it (grudgingly) and it was removed after the epidemic had already peaked

• It took Snow years to convince the authorities that water was the problem, not smelly air, and to force the water company to change where it drew water from the Thames (which was right next to the outlet from one of Chadwick’s sewers!)

• Snow had help (William Farr, others)• Snow died in 1858; the cholera bacterium was not discovered

until 1884 and “proven” by Koch to cause cholera

• In response to Snow’s analysis, the Board of Health conducted its own study of the neighborhood and collected the following information:

– Quality of ventilation of streets and buildings– Proximity of smelly slaughter-houses, noxious industries, graveyards– Smells in the streets and their sources (gutters, etc.)– Smells emanating from houses and their sources (water closets, cesspools)– Presence of new, closed as opposed to open sewers– Amount of waste (“filth”) in streets, houses and in basements of houses, and

smell– Whether cases of disease predominantly occurred in low versus upper floors of

buildings*– Personal cleanliness of residents (and whether they smell)– Number of deaths in each house and number of survivors*– Sources and quality (murkiness, smell) of water*

Cholera Story Wrap-up

* Data later used by Snow, but discarded by Board of Health

• Steven Johnson, author of “The Ghost Map”:– “The decision to remove the handle was not based

on meteorological charts or social prejudice or watered-down medieval humorology; it was based on a methodological survey of the actual social patterns of the epidemic, confirming predictions put forward by an underlying theory of the disease’s effect on the human body ... But learning to listen to reason takes time …”

Another history lesson (if there’s still time)Luis-Rene Villerme (1782-1863)

Death Rate (per 1,000)

Arrondissement Tax Exempt (%) 1822-1826 From Cholera

Montmartre 7 14.1 11.1Chaussee d'Antin 11 14.9 9.3Roule, Tuileries 11 15.2 12.2St Honore, Louvre 15 16.1 18.5Luxembourg 19 16.4 58.8

Porte St Denis, Temple 21 17.2 16.1Fuabourg St Denis 22 15.6 14.9St Avoie 22 16.9 29.4Monnaie, Invalides 23 20.4 29.4Ile St Louis 31 20.0 45.5St Antoine 32 21.7 27.8Jardin du Roi 38 90.9 28.6

Explain “arrondissement” and Tax exemptPrompt for TPS #5: What might explain the nonrandom pattern of data in this table?

Poverty Disease (Social Disruption)

PovertyDisease (miasma) (Social Disruption)

Villerme’s Interpretation

Chadwick’s Interpretation

Solution:- Redistribute wealth, provide social support and eliminate poverty- Improve health, reduce disease and social disruption

Solution:- Clean up environment, improve health and reduce disease- Reduce poverty and social disruption

Which of the following statements do you agree with:

A. “Poverty causes drug abuse and mental illness”B. “Mental illness causes poverty and drug abuse”

a. Ab. Bc. Neither A or Bd. Don’t know

Clicker Question #4: Prompt = Mental Illness is known to be associatedwith drug abuse and poverty. Clue: This is an actual question that was heatedly debated in the 1970’s

Final TPS (or Homework)

How would you determine which is the “best” answer?What “evidence” do you need to collect?What would you do with your results?Are there any other possible explanations?