EPIDEMIOLOGY
Study the occurrence and distribution of diseases
as well as distribution of determinants of health
state or events in specified population and the
application of this study to control health
problems
Field of science dealing with the relationship of
the various factors which determine the
frequencies and distribution of an infectious
process. A disease or a physiological state in
human community.
Study of the behavior of disease in the
community rather than in individual patients and
includes the study of reservoirs and sources of
human disease.
•Studies the patterns of disease occurrence in
human populations and the factors that influence
this pattern. The term obviously is related to
epidemic (derived form the Greek word” upon the people” meaning leading the people)
C-E. A. Winslow, the great public health leader of
the early 20th century, called epidemiology
“the diagnostic discipline of public health.”
Epidemic
- an increase in the frequency (incidence) of a
disease above the usual and expected rate, which
is called the endemic rate., thus epidemiology
count cases of a disease, and when they detect the
sign of epidemic, they ask who, when and where
questions.
•Who is getting the disease
•Where and when the disease is occurring
•From this information, they can often make
informed guesses as to why it is occurring.
Notifiable disease- surveillance made by the government before many people start dying.
The timely reporting of cases of notifiable disease allows public health authorities to detect an
emerging epidemic at an early stage.
A typical Epidemiologic Investigation- Outbreak of hepatitis and Food poisoning
•The ultimate goal is to use this knowledge to
control and prevent the spread of disease.
John Snow- father of modern epidemiology
- Study about cholera.
Two main areas of investigation
1. Describes the distribution of health status in
terms of age, gender, race, geography, and time.
2. Patterns of disease distribution in terms of causal
factor
•In epidemiology of any disease or event, one
studies the factor which contribute to its causation
and behavior- AGENT, HOST, ENVIRONMENT
•Epidemiology concept maintains that there can be
no single cause of disease
Uses of Epidemiology
1. Study the history of the health population and the rise and fall of diseases and changes in their
character
2. Diagnose the health of the community and the condition of the people.
3. Study the work of health services with a view of improving them
4. Estimate the risk of diseases, accidents, detects and the changes avoiding them
5. Complete the clinical feature of chronic disease and describe their natural history
6. Search for cause of health and disease
Agent is any element, substance or force whether
living or non-living thing; the presence or absence
can initiate or perpetuate a disease process.
Types of Agent
1. This could be living or non-living things, physical or
mechanical in nature such as extremes of
temperature, light electricity.
2. They could be chemicals- endogenous (within the
body) or exogenous (poison)
Characteristics of Agent of disease
1. Inherent characteristics - feature, biological requirement, chemical composition, resistance
2. Characteristic in relation to the environment- refers to the reservoir and source of infection and
modes of transmission.
3. Characteristic directly related to man
a. Infectivity- ability to gain access and adapt to the human host to the extent of finding of finding
lodgement and multiplication
b. Pathogenicity- measures the ability of agent when lodged in the body set up a specific reaction
c. Virulence- refers to the severity of the reaction produce and is usually measured in terms of fatality.
d. Antigenicity- ability to stimulate the host to produce antibody
Modes of Transmission
1.Direct transmission- immediate transfer of infectious agent a receptive
portal of entry
2. Indirect transmission
a. Vehicle borne- contaminated inanimate objects or materials
b. Vector-borne- from other living organism (ex. Insects)
c. Mechanical vector
d. Biological vector
3. Airborne- dissemination of microbial aerosols to a suitable portal of
entry usually the respiratory tract
a. Droplet nuclei- usually small residues which result from evaporation of
fluid from droplets emitted by an infected host
b. Dust
THE HOST FACTOR OF DISEASE
1.Age
2. Sex
3. Race
4. Habits, Customs and religions
5. Exposure to agent
6. Defense mechanism of the host
Humoral defense- these are cells in our body like plasma cells and lymphocytes
that produce antibodies to neutralize harmful effects of the infectious agents
and body fluids in our body that possess substance that have antimicrobial
properties
Cellular defense- there are cells in our body like macrophages and neutrophils
involve in the process of phagocytocis.
THE ENVIRONMENTAL FACTORS
OF DISEASE
Environment- sum total of an organism’s external
surrounding conditions and influences that affect
its life and development
•Physical Environment
•climate- certain disease have seasonal distribution
•Geography and location
•Biologic Environment- living environment of man
consist of plants, animals and fellow human
beings.
Incubation Period
•Time between exposure to infectious agent up to the time of appearance of the earliest signs and
symptoms
1. Clinical incubation period- the time between exposure to a pathogenic organism and the onset of
symptoms of a disease.
2. Biological Incubation Period- The time taken by the parasite to complete its development in the
definite host (from the time of entry of the infective larvae to the presence of microfilariae) is called the
Intrinsic incubation period (Biological incubation).
•ISOLATION
As applied to patient, separation for the period of communicability, of infected persons or animals from
others in such places and under such conditions as to prevent or limit the effect of the direct or indirect
transmission of the infectious agent from those infected to those who are susceptible or who may
spread the disease agent.
1.Strict isolation- this category is designed to prevent transmission of
highly contagious or virulent infectious that may spread by direct
contact or droplet.
2. Contact isolation- for less highly transmissible or serious infections,
for disease or conditions which are spread primarily by close or direct contact.
3. Respiratory isolation- to prevent transmission of infectious diseases
over short distance through the air
4. Tuberculosis isolation (AFB isolation)- for patient with pulmonary
tuberculosis who have a positive sputum smear or chest x-rays which
strongly suggest active tuberculosis
1.Enteric Precautions- for infectious transmitted by direct or indirect contact with feces purulent
material or drainage from an infected body site
2. Drainage/secretion Precautions- to prevent infections transmitted by direct or indirect contact with
purulent material or drainage from an infected body site.
3. Blood/body fluid Precautions- to prevent infections that are transmitted by direct or indirect contact
with infected blood or body fluids.
•QUARANTINE- restriction of the activities of a well or animals who have been exposed to a case of
communicable diseases during its period of communicability to prevent disease transmission during
incubation of infection should occur.
1.Absolute or Complete Quarantine
Limitation of movement of those exposed to a
communicable disease for a period of time not
longer than the longest usual incubation period
of that disease.
1. Modified Quarantine
Selective, partial limitation of freedom of
movements of contacts
1. Pre-pathogenesis
- This is the phase before man is involved. Through the interaction of the agent, the host and
environmental factors, the agent finally reaches man.
- It maybe said that everyone is in the period of pre-pathogenesis of many diseases because agents are
present in the environment where man lives
2. Pathogenesis
- This phases includes the successful invasion and establishment of the agent in the hos
