2. Defination
It is the study of the distribution and determinants of disease frequency in
human population.
The three closely interrelated components are :
Distribution
Determinants
Frequency
They encompass the epidemiological principles and methods.
3. Epidemiology components
1. Measurement of disease frequency: Means quantification of existence or
diseases occurrence.
2. Distribution of disease: considers questions like who is getting the disease in
the population , where and when is the disease occurring. This compares
different populations, groups or between periods of observation.
3. Determinants of disease: This is to test an epidemiology hypothesis for we
need to know the frequency and distribution. Data is collected and any
association Nissan established.
4. Why study epidemiology
i. To identify the cause of a disease and the risk factors that increases a
person's risk for a disease
ii. To determine the extend of the disease found in the community
iii. To study the natural history of a disease
iv. To evaluate new therapeutic and preventive measures
5. Epidemiology and prevention
Primary's prevent: Actions taken to prevent disease from occurring
Secondary prevention: identify those people who have develops the disease
through screening and early intervention.
Tertiary prevention : rehabilitation of people who have been devastated by
disiseas
6. Dynamic of disease transmission
• Disease does not occur in a vacuum. It arises on interaction of three
dynamics.
I. Host (a person)
II. Agent ( a bacterium)
III. Environment ( contaminated water supply)
• Hence, disease has been classically described as the result of an
epidemiological triad
8. Transmission of diseases
1) Direct or indirect fashion: person to person, direct contact or disease can
be transmitted indirectly through contaminated water supply.
2) Horizontal or vertical: Horizontal is from one person to another, and
vertical is from one hey to another through genetic
9. Clinical and subclinical disease
• The iceberg concept: just as most iceberg is submerged in water, hidden
from view with only its tip visible, so is with disease. That's only clinical
illness is readily apparent.
• Clinical disease is that which is characterized busy signs and symptoms
• Non clinical diseases is:
Preclinical Disease: Disease that is not to yet apparent but it is in stage that it
is going to progress to clinical disease
10. Subclinical Disease: Disease that is not clinically apparent and it is not
destined to become clinically apparent . Diagnosed by serology
Persistent (chronic) disease: A person fails to shake off the infection and it
persists for years at times for life.
11. Carrier status
• In this situation the individual harbor the organisms but is not infected as
measured by serological studies or is not clinically il.
• The person can still infect others
12. Factors that may be associated with increased risk of human diseases
Host characteristics Types of agents and examples Environmental factors
Age Biologic ( bacteria, viruses) Temperatures
Sex Chemical (poison,alcohol, smoke) Humidity
Race Physical (trauma,radiation,fire) Altitudes
Religion Nutritional (lack, excess) Crowding
Customs Housings
Occupation Neighborhood
Genetic profile Water
Marital status Milk
Family background Food
Previous disease Radiation
Immune status Pollution: air, Noise
13. Endemic, epidemic and pandemic
Endemic: habitual presence of a disease within a given geographical area
Epidemic: the occurrence in a community or region of a group of illness of
similar nature clearly in excess of normal expectancy derived from a
common cause.
Pandemic refers to word wide disease
14. Disease outbreaks
• Let assume that a food becomes contaminated with microorganism.
• Common vehicle exposure: when an outbreak results in the group of
people who have eaten the food because all the cases that developed were
persons who were directly exposed to the food. This results to single
exposure .
• When the food is served more than ones then it is multiple exposures
to,people who eat it more than once
15. Determinants of disease outbreaks
i. People in the population who are susceptible and at risk of disease
ii. People who are not susceptible or immune to the disease
16. Herd immunity
• The ability of a large number of people in a population to resist a disease
which they are immune of.
• If a large percentage in the population is immune, then the entire population
is likely to be protected .
• Herd immunity occurs because disease in a population spreads from one
person to another. Thus once the disease reaches a indivinduals in a
population who are immune the disease is less likely to penetrate.
17. Measuring the occurrence of disease
Healthy
Disease onset Symptoms seek care diagnosis treatment out comes
( cure, control, disability, death)
18. History of disease
As seen in the above figure, an individual is health….Has no disease.
At some point, the biologic onset of disease occurs.
The person is often unaware of when the disease began. Later; symptoms
develop and lead the patient to seek medical care.
In certain situations the patient may be admitted or hospitalized for diagnosis
or treatment or both.
In any case, diagnosis is made and treatment initiated. One of several outcomes
can result : cure, control of the disease, disability, or death.
19. Sources of health records
I. Questionnaires or interview from the patient
II. Health insurance
III. Hospital records
IV. Physician records
V. Medical records
