Midterm Review Flashcards
1 Contrast between PH with medicine
Ph focuses on prevention
– Achievements may be more difficult to recognize
– Less attention and funding
– Less than 5% of U.S. health spending is on public health
- Yet public health programs clearly save lives and medical costs
– U.S. life expectancy ↑ by ~30 years over 20th cent
– Only ~5 of the 30 years can be attributed to medical care
– Public health: nutrition, sanitation, housing, occupational safety, etc.
– What was one of the biggest changes to health/disease over the 20th
century? Cleaner air and water! - Politics:
– $ How much “health” are we willing to fund?
– What are we willing to give up? - Individual liberties, corporate profits, etc.
– Is our emphasis on curing disease rather than preventing it out of
control?
slide 7
What was one of the biggest changes to health/disease over the 20th
century? Cleaner air and water!
- British Cholera Epidemic
1848-1849:
– 616 deaths prompted
Snow (and others) to
investigate causes
– Based on his clinical
experience and review of
epidemiologic
characteristics of cholera,
Snow formulated a theory
of causation and
transmission of the disease
slide 13
John Snow Cholera Epidemic
Snow’s hypothesis
* Observations:
– A gastrointestinal disease, therefore causal agent was likely
ingested
– Diarrhea as most prominent symptom, therefore causal
agent likely left the body by this route
– If cholera excretions contaminated rivers from which
drinking water was taken, then the disease could be widely
disseminated
* Causal Hypothesis:
– Sewage-contaminated drinking water was a causal agent
for the cholera epidemic
slide 14
Layers of Prevention and Intervention
- Primary prevention
– Prevent illness/injury from occurring
– Discourage risk behaviors (e.g., smoking) - Secondary prevention
– Minimize severity or damage after event has occurred
– Screening for early stages - Tertiary prevention
– Further minimize overall disability
– Not always a huge distinction from “secondary”
– Medical treatment and rehabilitation
slide 9
Why is Public Health Controversial?
- Moral and religious opposition
– Sex education
– Provision of contraception
– Clean needle programs
– Safe and legal abortions - Political interference with science and research funding
– E.g., stem cell research, HIV research, climate change - Companies and private businesses are not always motivated to help their customers. They seek to earn profits.
slide 10
Powers and Responsibilities of Government
- U.S Constitution states that the fundamental purpose of the government is “to promote the general welfare”
-Reserve clause: health care is not mentioned in the Constitution so the responsibility for public health belongs to the states
-Interstate commerce provision justifies the activities of the Food and Drug Administration (FDA)
-Power to tax and spend is widely used by federal government to control public health policy (The federal government provides 65% of the funding for Medicaid)
slide 11
A word about global health governance
- World Health Organization (WHO)
– Serves as a clearinghouse for science that informs public health at global and regional levels.
– Can issue policy recommendations, but does not have a “jurisdiction” and therefore cannot enforce rules.
– Coordinates efforts at a global level – especially useful in pandemic response.
– Useful to think of WHO’s role as one of health diplomacy.
slide 12
“Descriptive” epidemiology
- Who, Where, When (and how many)
- Understand the state of population health and how it is changing
– E.g., Are we making progress in CVD, cancer?
– E.g., Are some diseases on the rise (or new)?
– Prompts questions of: WHY? - Interventions (e.g., screening, etc.), treatments, changes to
environment or behavior. - Understand disparities (e.g., by race-ethnicity, age, gender/sex, SES)
slide 15
Endemic vs Epidemic
- Endemic = the usual and expected rate of a
disease in a population - Epidemic = an increase in the frequency of a
disease above the usual and expected rate
slide 16
Analytic epi (How)
- We already know person, place, time because of the descriptive epi so we need to look at relationships to learn HOW epidemics occur:
– Explain why and how a health problem occurs
– Describe association between exposure and outcome
– Test a hypothesis about the cause of disease by studying how exposures relate to the outcome - These studies look at:
– Hosts
– Environments
– Agents
slide 17-18
Epidemiology
The study of the distribution, causes, and effects of health and disease in defined populations
* Distribution
* Causes (and effects)
– Really difficult to prove “causation”
– We are attempting to find/show associations
* E.g., HRT is associated with an increased risk of heart disease
* Correlation does not imply causation
– Also investigating risk factors (might not refer to as a “cause” per se
– Sometimes we say “disease.” Sometimes we say “health outcome.” These terms are often used interchangeably.
slide 19
Investigating Associations:
4 Types of Study Designs in Epi
- Cross-sectional
- Prospective cohort (longitudinal) – observational*
- Case-control – observational*
- Experimental/Interventional**
*Observational studies pose the least risk of harm.
**Experimental studies can potentially cause harm.
slide 20
Prospective Cohort Study
- Start with a defined population (cohort)…
- Some are exposed and some unexposed …
- Follow up and compare on development of disease
- Text examples
– Framingham Heart Study - CVD risk factors (BP, cholesterol, smoking) and heart disease
- But we didn’t know they were risk factors!
- There was no concept of “high” blood pressure (“hypertension”); considered a normal process of aging
– Nurses’ Health Study
* Oral contraceptives and breast cancer
* Regular consumption of alcohol increases risk of breast
cancer by 10% to 40%
slide 21-22
Case-Control Study
- Again, examine relation of an exposure to a disease
- Identify people with the disease (cases) match to people w/o the disease (controls) and …
- Start with two groups: disease (cases) and no disease (controls), and compare their prior exposure status
- Text examples
– EMS and L-tryptophan
– Reye’s syndrome and aspirin use in children - A primary distinction from cohort study is starting with cases rather than a cohort (pre-defined pop)
- Selection of cases
– Sources: hospitals, physician practices, disease registries, etc. (Be mindful of generalizability!) - Case-control study saves time over cohort. WHY?
– What if you’re waiting around for incident cases? - Advantages of over cohort designs
– Inexpensive
– Shorter time
– Requires smaller sample (good when disease rare) - Limitations
– Recall bias
– Difficulties selecting controls
– Cannot estimate disease incidence or prevalence.
WHY?
slide 23-26
Case study diagram
slide 27-37
Experimental/Interventional:
Randomized controlled trials (RCTs)
- Gold standard in research
– Control group
– Randomization - Planned experiment where investigators assign study participants to either an intervention or control group
- Trials are designed to test efficacy of intervention or clinical treatment
- They are often blinded to protect against breaches in ethics
– Blind – the participants don’t know treatment status, researchers know treatment status
– Double blind – neither participants nor researchers know treatment status
slide 38
Measuring Disease
Prevalence vs. Incidence
- Prevalence: # people who currently have a condition
– Often expressed as a proportion
– Implies a population at risk (the denominator)
– Sometimes called frequency
– E.g., 5%, or 50/1000 persons - Incidence: # of new cases/diagnoses
– Usually includes a time dimension – WHY?
– Also incorporates dimensions used/implied in prevalence
(i.e., 3 dimensions)
– E.g., 50/year, 50/1000 persons/year
slide 39
Prevalence
- Number of existing cases of disease in a
population - Can be expressed as a percentage or number of cases per unit size of population
- Indication of extent of health problem; helps us determine need and allocation of resources
Prevalence = Number of all cases (new + old)/Total population
slide 40
Incidence
- Rate of development of disease in a population over a certain time period
- Can help identify emerging diseases, reemerging diseases, or outbreaks
Incidence = Number of new cases/Total population at risk
slide 41
Prevalence vs. Incidence
Can be very different depending on the outcome
- Chronic and incurable (e.g., HIV/AIDS, arthritis, diabetes)
– Prevalence > incidence - Common and short-lived (e.g., STDs)
– Incidence > prevalence - Rapidly fatal (e.g., pancreatic cancer, acute
leukemia, Ebola, Dengue Hemorrhagic Fever)
– Incidence > prevalence
slide 47
