Introduction to Epidemiology

Question 1

What is Epidemiology?

Answer 1

The study of the distribution & determinants of health, disease & injury in human populations

Question 2

Why are some people healthy/sick and others not?

Question 3

Epidemiology is based on 2 assumptions:

Answer 3

1. Human disease does not occur at random
2. Human disease has causal & preventive factors that can be identified through systematic investigation

Question 4

Greek:

Answer 4

“the study of what is upon the people”

Question 5

Epidemiology describes the

Answer 5

frequency & patterns of morbidity & mortality in terms of person, place, or time.

Question 6

Goal of epidemiology

Answer 6

To describe or explain the occurrence of health, disease, injury or health-related conditions in a community or group of people.

Question 7

APPLICATIONS of epidemiology

Answer 7

Identifying Risk Factors for Disease  Disease Causation

Evaluating treatment efficacy (e.g. randomized controlled trials)

Investigating disease outbreaks

Other uses:
Public health planning & prioritizing, needs assessments, setting objectives, program evaluation; Formulating health policy; Understanding natural history of disease; Estimation of individual risk; Completing the clinical picture of a disease (physicians may have inaccurate view of severity & distribution of Dx, since only some people seek treatment…).

Question 8

Outbreak =Epidemic what dpes that mean

Answer 8

A clear increase in number of “cases” of a disease or health-related condition over normal baseline levels

Question 9

The pyramid or iceberg of disease

Answer 9

tip of the iceberg:
Diseased: diagnosed, controlled and uncontrolled

The bummock is
Undiagnosed or wrongly diagnosed disease
risk factors for disease
free of risk factors

Question 10

3 Types of Epidemiology:

Answer 10

Descriptive
Analytic Epidemiology
Clinical Epidemiology

Question 11

3 Types of Epidemiology: Descriptive

Answer 11

Describes the Frequency & Patterns (distribution) of morbidity & mortality:
Person-Place-Time  Who-Where-When
e.g. populations where a dx does/does not occur, most common geographic locations, frequency over time

How would you describe the distribution of a disease or health-related condition?

Question 12

3 Types of Epidemiology: Analytic Epidemiology

Answer 12

Determinants of disease:

Why/How?  Causes

Testing hypotheses formulated from descriptive studies: The most challenging aspect of epidemiology

What are the factors associated with a disease or health-related condition?
Can we predict (& therefore possibly prevent) disease, injury, & other health conditions?

Question 13

3 Types of Epidemiology: Clinical Epidemiology

Answer 13

Patient oriented  Seeks to aid decision making about diagnosis, prognosis, & treatment of disease.
Deterrents
Goal: To prevent, reduce, or control morbidity & mortality in human populations.

So we’ve 1) Described the distribution, and 2) Identified the determinants… now 3)
 How do we stop it?

Question 14

Evolution of Epidemiology

Answer 14

Started as an attempt to explain disease in a systematic way

Pandemic: 1347-1351, the Plague killed >30% (25M) of the population of Western Europe, & 60M people worldwide.

Question 15

“Black Death:” How to explain the devastation caused by this & other diseases?

Question 16

The early pioneers of epidemiogly: Hippocrates

Answer 16

Hippocrates (460-377 B.C.): One of the first to base his (not always correct) conclusions on observations – rational explanations, individuals & populations, association of environmental/other factors.

Factors causing disease might be sought in:
* Air (hot & cold winds);
* Water (marshy, soft, hard, from rocky soil);
* Places (lacking vegetation, lacking water, too much water, elevation, cold);
* Personal habits (drinking, excess eating, lack of exercise & labour).

Question 17

The early pioneers of epidemiogly: John Graunt (1620-1674):
“Father of Biostatistics”

Answer 17

Published weekly & annual recording of births & deaths (“Bills of Mortality”); Quantified disease patterns; Associated births & deaths with age, sex, other factors.
Higher frequency of births & deaths in M vs. F;
Seasonal fluctuation in deaths;
Patterns in infant mortality rates;
Developed quantitative methods.

Question 18

The early pioneers of epidemiogly: Dr. John Snow(1813 - 1858)

Answer 18

Transmission of Cholera through contaminated water
“For his persistent efforts to determine how cholera was spread and for the statistical mapping methods he initiated, John Snow is widely considered to be the father of [modern] epidemiology.”

Question 19

Spread of cholera through water

Answer 19

1849: Cholera deaths highest in districts served by 2 specific water companies, both getting water from sewage-contaminated Thames River.
1852: 1 company relocated to uncontaminated area.
1853: Another Cholera outbreak  Compare deaths in districts served by each water company: Over 5x higher in districts served by company drawing water from contaminated area!

Question 20

Association between sewage-contaminated drinking water and Cholera deaths?

Answer 20

• Focus on districts served by BOTH water companies

Found that households served by 1 of the companies had substantially higher death rates from cholera than those served by the other
Therefore Snow established that cholera was a water-borne disease.

Question 21

1854 – “The Case of the Broad St. Pump”

Answer 21

13 pumps serving London area of Cholera outbreak.
Snow mapped homes and workplaces of those who died during outbreak, + water-pump sites.

Snow noticed that cases clustered around a pump on Broad St
Carefully eliminated all other possible explanations, & investigated the water sources of those who died
Linked ALL cases to this pump, confirming that cholera was a water-borne disease.
removal of water pump handle = end of outbreak!

Perceived as a major event in the history of public health – regarded as the founding event of the science of epidemiology.

Question 22

James Lind (1716-1794) Naval surgeon
How did he contribute to epidemiology?

Answer 22

Divided 12 soldiers suffering from scurvy into 6 pairs, each received a different dietary supplement.
 Pair receiving citrus fruit showed improvement.

Question 23

Edward Jenner (1749-1823) English surgeon
How did he contribute to epidemiology?

Answer 23

First to immunize against smallpox using cowpox vaccine, after observing that milkmaids infected with cowpox were immune to smallpox.
Successfully inoculated 23 people with cowpox
 paved the way for preventive medicine.

Question 24

Austin Bradford-Hill (1897-1991)
How did he contribute to epidemiology?

Answer 24

1950s studies proved a causal relation between smoking & lung cancer - the results of these studies sped up the growth of epidemiology.
* Developed a check-list to judge the causality of an association

Question 25

“Bradford-Hill Criteria” 1965:

Answer 25

Strength Plausibility
Consistency Coherence
Specificity Experimental Evidence
Temporality Analogy
Biological Gradient

Question 26

Epidemiology in the 20th Century

Answer 26

Framingham Heart Study (1948) – in response to mounting epidemic of CVD in US in 1930s: why had it become the #1 killer by late 1040s? Coined the term “risk factors”.

U.S. National Health Examination Survey (1959) – 140,000 people survey since then!

Canadian Health Measures Survey (2007)

Question 27

Epidemiology in UOR

Answer 27

Interested in exploring physical activity (PA) & sedentary behaviour (SB) in the population?  This is the place to be! 
Healthy + Clinical Populations & Sub-Populations
Across the lifespan: Children, Adults, Older Adults
PA & SB trends in the population
Correlates and determinants of PA & SB
Associations of PA & SB with cardiometabolic, psychosocial, & quality of life outcomes
We use large pre-existing databases (e.g. Statistics Canada) & also collect our own data