Introduction to Epidemiology Flashcards
What is Epidemiology?
The study of the distribution & determinants of health, disease & injury in human populations
Why are some people healthy/sick and others not?
Epidemiology is based on 2 assumptions:
- Human disease does not occur at random
- Human disease has causal & preventive factors that can be identified through systematic investigation
Greek:
“the study of what is upon the people”
Epidemiology describes the
frequency & patterns of morbidity & mortality in terms of person, place, or time.
Goal of epidemiology
To describe or explain the occurrence of health, disease, injury or health-related conditions in a community or group of people.
APPLICATIONS of epidemiology
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…).
Outbreak =Epidemic what dpes that mean
A clear increase in number of “cases” of a disease or health-related condition over normal baseline levels
The pyramid or iceberg of disease
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
3 Types of Epidemiology:
Descriptive
Analytic Epidemiology
Clinical Epidemiology
3 Types of Epidemiology: Descriptive
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?
3 Types of Epidemiology: Analytic Epidemiology
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?
3 Types of Epidemiology: Clinical Epidemiology
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?
Evolution of Epidemiology
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.
“Black Death:” How to explain the devastation caused by this & other diseases?
The early pioneers of epidemiogly: Hippocrates
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).
The early pioneers of epidemiogly: John Graunt (1620-1674):
“Father of Biostatistics”
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.
The early pioneers of epidemiogly: Dr. John Snow(1813 - 1858)
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.”
Spread of cholera through water
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!
Association between sewage-contaminated drinking water and Cholera deaths?
- 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.
1854 – “The Case of the Broad St. Pump”
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.
James Lind (1716-1794) Naval surgeon
How did he contribute to epidemiology?
Divided 12 soldiers suffering from scurvy into 6 pairs, each received a different dietary supplement.
Pair receiving citrus fruit showed improvement.
Edward Jenner (1749-1823) English surgeon
How did he contribute to epidemiology?
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.
Austin Bradford-Hill (1897-1991)
How did he contribute to epidemiology?
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
