What is it?

• The study of  distribution and factors contributing to the development of disease in human populations.
• Epidemiology is highly quantitative based on statistics and research methodologies.

Distribution:

• Looking at frequencies and patterns of cases, the making hypotheses.
• Three factors are considered:

- The person: gender, age, sex.
- The Place: where?, why?
- The Time:

Determinates

• The risk factors: looks at how? And why?

Health-Related States

• Historically concentrated on infectious diseases, however now broadening to,
• Chronic disease.
• Environmental factors
• Behavioural factors eg Violence – domestic, family or community.
• Injuries.

Population.

• Focuses on groups of people. Instead of individuals.

Application.

• Used in prevention techniques. In three stages.
• Primary: stopping illness eg washing hands.
• Secondary: stopping transmission.
• Tertiary: minimising the impact on immediate environment.

Epidemiologic Milestones:

1. Lung Cancer link to smoking.
2. Folate & Spina Bifida
3. AIDS Aquired Immune Deficiency Syndrome
4. Legionnaires’ Disease.
5. SIDS Sudden Infant Death Syndrome
6. Chronic Fatigue Syndrome
7. Gulf war syndrome.
8. Alzheimers disease
9. Cellular phone & Power lines.
10.Thalydamide, Asbestosis

Why Teach Epidemiology?

Improves reasoning and research skills, analysing and problem solving.
Develop good health practices

Causation

X  ----------(   Y
Why? Prevention depends on being able to understand the cause.

Criteria for Demonstrating Causation

Relative Risk =  frequency of risk/ frequency of no risk.
Eg. RR = use of cell phone/ no use of cell phone.
Strength of Association
No association = 1.0
Protection   < 1.0
Cause > 1.0

Consistency association must be repeated in different situations to give credibility.

Temporality cause must precede the effect

Plausibility must make biologic sense.

Biologic gradient - must be a dose -response relationship.
Eg        Dose group  /  Response
 None   1 person / 10,000
 Little risk  2/ 10,000
 Some risk  5/ 10,000
 Lot of risk  30/10,000

Type of Scientific Studies
a.) Experimental
Randomise into groups
Apply treatment or exposure to test group
Observe outcome

b.) Observational Studies
Descriptive vs analytical
Attempt to duplicate the above
Subjects elect which group they are in
Researcher only observes

c.) Descriptive Studies
Address who, what, wher, when.
Help identify those groups, locations or times most involved with the problem.
Helps focus on prevention / control.
Help generate hypotheses regarding possible cause

Part 2:
Surveillance
The systematic, ongoing collection, tabulation and analysis of information about the occurrence of illness and or risk factors in a specific population and the dissemination of information to those who need to know.

Purposes.
Identify outbreaks and clusters of cases
Evaluate the effectiveness of interventions eg use of vaccines.
Determine where/how to allocate resources
Generate hypotheses about knowing more about illness and the treatment.
Monitor the trends and patterns in disease occurrence.

Types & Examples of Surveillance

1. Active                        ---------------------               Passive
   Going and collecting data    -----------                    rely on people telling you

2. Biological /sentinal / resistance systems
Using of experimental procedures to gather data eg. Theuse of canaries down the mines to indicate gas leaks.
3. Notifiable Disease Reporting System
Doctors are required to report occureences of certain diseases eg sexually transmitted disease.
4. Hospital infection Surveillance
This data is collected by the hospitals as a refection of there work.
5. Risk factor surveys
Survey that ask people about their activity, then linking there habits to the chances of getting an illness.

When designing an Investigation it is important to define your sample population. Below is a guide to the styles of groups you may wish to use.
 
 
 

	Truly have the condition	Truly do not have the condition
Reported to have the condition	A	B False +ve
Reported not to have the condition	C False -ve	D

 
The goal in defining the groups as below is to minimize the B's & C's

Surveillance Definitions:
Sensitive: should include all cases of interest.
Specific: should only  include cases of interest.
May be stratified - possible/ probable / confirmed./ not ill.

Example Defining Injury.

Group 1
Points:
Change in structure of human body
Requires medical treatment
Result of an event/ not spontaneous.
To become more specific. Categories
Major.
 Reported to the doctor
 Broken bones, major bleeding, effects 10% of the body, risk to life.
 Need for medical treatment.
Moderate.
Reported to nurse
Bruised, strains, sprains,
No risk to life
Minor
Not reported to nurse
No bleeding, no drugs

Group 2: Injury.
Points:
Involves getting hurt, bruised, sprains, strains or wounded.
Causes suffering and pain.
Categories
1. Self inflicted
2. Intentional
3. Non-Intentional
4. Psychological

Part 3

Center for Disease Control & Prevention (CDC) website
http://www.cdc.gov
Set of Lectures on Epimemiology
www.pit. edu/~super1

Outbreak / Epidemic
Unusual or unexpected increase in the number of cases of a particular illness or event in a given population

Type of outbreaks
Point source one particular area. Vs continuing
Mode of transmission (food borne, water borne, vectors etc.)
Setting where the outbreak occurs
Disease the type of illness
Term can be mixed to clearly define the situation.
Eg In creek bed county Malaria …..

Outbreaks recognised by.
Surveillance detected through organised channels.
Community reports some one reporting in
 

Steps of an Outbreak Investigation.
1.  Prepare for field work
2.  Extablish existance of an outbreak
3.  Verify the diagnosis
4.  Define and identify cases
5.  Describe and oriet the data in terms of time, place and person.
6.  Develop hypotheses
7.  Evaluate hypotheses
8.  Refine hypotheses and follow up
9.  Implement control and prevention measures.
10. Communicate findings

Establish existence of an outbreak

Definitions.
Surveillance records
Other data sources
Comparisons with data from other areas
Evaluate possible changes in reporting
Other reasons to investigate outbreak

Define and identify cases
Case definition
Time, Place and Time..

Types of Studies.

1. Cohort Study
Used for well define population.
Uses Relative risk  see above.
2. Case Study Control
Useful when we have a small numberor do not know entire group
Start with group with disease
Select a group without the disease
Obtain information about past exposures.
Use Odds ratio
 
 

	Cases	Controls
Lot
Some
Little
Total

Eg Odds ratio
lot = (lot case * Total controls) / (total cases* lot controls)
Some = (some case * Total controls) / (total cases* some controls)
Little = (Little case * Total controls) / (total cases* little controls)