Epidemiology Mcb 4276 Ucf

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Top 5 Mortality in 1900

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1. Pneumonia
2. tuberculosis
3. diarrhea & enteritis
4. heart disease
5. chronic nephritis

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3 Temporal patterns

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• Short-term: Brief, unexpected outbreaks
• Cyclic patterns: predictable
• Secular Trends: Long-term changes in Morbidity and Mortality patterns

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Epidemiology

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Distribution and Determinants of disease frequency in pop

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Epidemic

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at a grand scale (in group- increase in # of what is normally expected) – excess of normal expectancy

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Pandemic

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international borders (worldwide epidemic)

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Endemic

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Habitual present of disease in an area or constant presence and normally expected

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Hippocrates

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• 1st epidemiology
• rational vs. supernatural explanation
• Disease not only affects individuals but also pop.
• Differentiated between endemic and epidemic
• Associates between environment and diseases

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Edward Jenner

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smallpox vaccine

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John snow

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cholera --> contaminated water

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Ignas Semmelweis

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childbed fever and washing hand

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Florence Nightingale

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statistic hygienic standards

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Louis Pasteur

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microbes cause disease & vaccination can control disease

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Robert Koch

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Germ Theory of Disease

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2 types of risk factors:

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1. Non-modifiable: characteristic cannot be changed.
Example: sex or age
2. Modifiable: characteristic can be changed.
Example: obesity, diet or lifestyle factors

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Types of preventions:

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1. Primary prevention
2. Secondary prevention
3. Tertiary prevention

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Primary prevention:

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a. Prevent the development of disease
b. Does not have the disease in question (yet).
i. Therefore, you can immunize that person.
c. If disease is environmentally induced: we can prevent that person’s exposure to the environmental factor

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Secondary prevention:

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a. Focus on early detection and fast treatment of disease- the purpose is to cure or slow the progression of disease.
b. Use test to screen:
i. Breast examination
ii. Mammogram
iii. Eye test
iv. Blood test
v. Etc.

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Tertiary prevention:

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a. Therapeutic and rehabilitative when disease is established.
i. Change lifestyle with rehab or hospital program, or medication

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Different stages of Disease (Dz):

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1. Clinical Dz: signs & symptoms
2. Non-Clinical Dz:

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List the types Non-Clinical Dz:

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• Preclinical Dz
• Sub-clinical Dz
• Persistent (chronic) Dz
• Latent Dz

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Preclinical Dz

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disease that is not yet clinically apparent, but destined to progress to clinical disease.

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Sub-clinical Dz

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Not yet clinically apparent and NOT destined to become clinical apparent.

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Persistent (chronic) Dz

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persists for years or lifetime

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Latent Dz

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Person infected w/ Dz but do not show signs and symptoms

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Active immunity

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when the body produces antibodies when you are infected or by vaccine

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Passive immunity

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when you acquire immunity by:
a. Injection of serum
b. Placental transfer
c. Breast feeding

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Acute (Active) Outbreak

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can be deductive or inductive

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deductive

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You go backward to see what cause Dz

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inductive

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You go forward to see what the Dz can cause.

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Steps to define acute outbreak:

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1. Define the epidemic:
a. Define the # of cases (numerator).
b. Define the population at risk (denominator).

2. Examine distribution of cases by: Time, place and time-place interactions.
3. Examine combinations of relevant variables.
4. Develop hypothesis.
5. Test hypothesis.
6. Control measures

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2 type of measure of disease frequency:

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PREVALENCE
INCIDENCE
1. Cumulative Incidence (CI)
2. Incidence rate (IR)

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PREVALENCE

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snapshot of proportion who exist with disease @ point in time.
Interpreted as the probability that person will have a disease at a point in time.

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PREVALENCE (P) =

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P = # of persons existing w/ disease
# of persons in total pop.

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INCIDENCE

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development of disease who are at risk over a period of time.

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2 type of measurement of incidence:

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Cumulative Incidence (CI)
Incidence rate (IR):

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Cumulative Incidence (CI):

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the portion of people who become disease over specific time.
CI is an estimate for the risk (probability) that a person will develop disease in a time frame.

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Cumulative Incidence CI =

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CI = # of new cases developing in specified time / Total population @ risk

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Incidence rate (IR)

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the rate at which new cases of disease occurs in a population at risk for disease.

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Incidence rate (IR)=

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IR = # of new cases developing over study period / Total person-time of observation

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Duration

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Once they get the disease

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Prevalence is proportional to incidence and avg. duration.

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Prevalence (P): P = I x avg. D ***under steady state***

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What does the prevalence Data measures?

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It measures the disease frequency

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To determine if study is valid:

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1. Chance
2. Bias
3. Confounding

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Chance

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a. Result due to random sampling variability
b. To measure the effect of chance is by doing a test of statistical significance.

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Null hypothesis (Ho) =

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NO association

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Case control

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Selection on basis of DISEASE status.

Investigator go back to determine if they had/had not exposure.

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Cohort

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Selection on basis of EXPOSURE status.

Investigator start with exposure status and track over time to see what happens to disease.

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Prospective cohort study

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study in which disease has not yet occurred at initiation of study.

Begin at midpoint and track to FUTURE to see what happens to dz upon exposure

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Retrospective Cohort study

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Dz occurred in the past prior to initiation of study.

Start w/ exposure status and track BACK to examine effect of exposure or non-exposure on dz.

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Intervention Study

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Comparison of an outcome (e.g. morbidity or mortality) between two groups of people deliberately subjected to different dietary or drug regimes.

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CI (exposed)

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# exposed cases/ # exposed

a / (a+b)

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CI (non-exposed)

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# non-exposed cases / # non-exposed

c / (c+d)

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Relative Risk (RR)

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indicate a measure of the strength of the association between an exposure and a disease.

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Risk ratio:

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CIR (cumulative incidence ratio)

CI (exposed)/ CI (non-exposed)

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Rate ratio:

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IRR (incidence rate ratio)

IR (exposed)/ IR (non-exposed)

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Risk Ratio = ?

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Rate ratio

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What is Relative Risk (RR)

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Tells those who are exposed have X times the risk of developing the outcome than the nonexposed

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What defines Relative Risk?

Hint: 4 things

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Ranges from 0 to infinity
Null value = No association:RR= 1
RR>1 = indicates a + association w/ increase risk of disease

RR<1 = indicates INVERSE association w/ decrease risk of disease

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Relative risk formula:

RR = ?

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RR = CI(E)/CI(ne)

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Can relative risk (RR) be calculated with case-control study?

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No, but RR is approximated by odds ratio (OR) = ad/bc

so calculated OR & interpret as relative risk

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ecological model

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Explain disease causation by imbalance of host, agent, & environmental factors
designed for communicable dz

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In ecological model, what factors affect human disease ?

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host characteristics
types of agents
environmental factors

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What are the steps in investigating an active outbreak?

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defining the number of cases
defining the pop. at risk
examining combinations of relevant variables
developing and testing hypotheses

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How do you calculate Relative risk?

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take the
CI (Exposed) / CI (non-exposed)

CI (exposed) = #of expose case/
# of exposed
a/ (a+b)
CI (non-exposed) = c/ (c+d)

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what is the difference between case control and retrospective cohort?

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case control: INVESTIGATOR goes back see when or not exposed

retrospective cohort: start w/ EXPOSED and go back when or not exposed.

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What method can you use to control variables in a study ?

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1.Randomly selecting the subject
2.remove the variable from the study
3.Match subjects in comparison groups by criteria
4.randomly assign subjects to either control or experimental group

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What does the null hypothesis mean?

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It means that the independent variable does not have an effect.

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What is the purpose of a control group?

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allow the researcher to determine the influence of external factors that are not suppose to influence the results of the study.