Nursing College – Mosul UniversityEpidemiology is a lateen, Greek wards Epi
(upon), on demos ( the people ), or
(population) as aggregation , and logy
knowledge, science the knowledge or study
of what happens to people . Epidemiology is
the study of the determinants and
distribution or frequency of health, disease,
and injuries in human populations .
Epidemiology is the science concerned with
the distribution and determinants of disease
or disability in a community .
EPIDEMIOLOGY is the study of the nature,cause, control and determinants of the frequency
and distribution of disease, disability, and death in
Epidemiology: the study of factors influencing the
transmission, distribution, prevention and control of
disease in a defined population
Epidemiology: the study of factors influencing the
occurrence, transmission , distribution, prevention and
control of disease in a defined population
On Airs, Waters, andPlaces
Idea that diseasemight be associated
Hippocrates (460 -375 B.C.)
The roots of epidemiology can be traced toHippocrates , Greek physician who lived from about
460 to 375 BC and who is sometimes referred to as the
first epidemiologist . Hippocrates and other of
Hippocratic school believed that disease not only
affects individuals but is a mass phenomenon . This
was one of the earliest associations of the occurrence
of disease with lifestyle and environmental factors ,
specifically geographic location. Epidemic and
pandemic diseases clearly prompted the development
of epidemiology as a science. In U.K. 1962 at past
epidemiology terms as : "society of London defined
Epidemics as including the disease classified zymotic
In Prussia between 1816 -1875 over 363.000 women died ofpuerperal fever . In the middle of the 19 th century in the
hospitals of Vienna (the major center of the world at that time)
about one of every eight women died of puerperal fever
An important clue in the source of the disease cane from
death of Semmelweis's friend Kolletshta who had died of an
infection as the result of a scalped wound he incurred while
doing an autopsy. The symptoms were the same as those seen
in the women suffering from puerperal fever. Semmelweis
reasoned that the same "poison" that had killed his friend was
probably on the hands of the medical students who did
autopsies and then attended the women in the first section
which had upper infections puerperal than the second section
but that person transmitted the infection by puerperal fever.
Ignas Semmelweis ( 1840 ’s) Pioneered hand washing to
help prevent the spread of
septic infections in mothers
Mary Mallon, a cook responsible for most famous outbreaks ofcarrier -borne disease in medical history
Recognized as carrier during 1904 N.Y. typhoid fever epidemic
When source of disease was traced, Mary had disappeared only
to resurface in 1907 when more cases occurred
Again Mary fled, but authorities led by George Soper , caught her
and had her quarantined on an island
In 1910 the health department released her on condition that she
never accept employment involving the handling of food
Four years later, Soper began looking for Mary again when two
new epidemics broke out; Mary had worked as a cook at both
She was found and returned to North Brother Island, where she
remained the rest of her life until a paralytic stroke in 1932 led to
her slow death, six years later
Typhoid Mary & George Soper
Typhoid MaryFoundation of epidemiology:
The ultimate goals of epidemiology are to determine the scale
and nature of human health problems, identify solutions to
prevent disease, and such as (HIV, HBV) in the health of
entire population .Also offers community health nurses a
specific methodology for assessing the health of aggregates.
Whether the community health nurse's goals are to improve a
population 's nutrition , control the spread of diseases deal
with health problems , protect and promote the health of
battered woman , or reduced the number of automobile crash
injuries and fatalities at specific intersection, epidemiologic
data essential. Epidemiology concerned with the study of
epidemics of infectious disease. In this term that use in past
widely because infectious diseases were responsible for large
proportion of the Morbidity and Mortality in the community.
Purpose of epidemiology:Epidemiology measures rate , persons , placed and time.
These appears the tools of epidemiology such as incubation
periods and epidemic curve during infections by age, sex, race,
vehicles or vectors, possible sources of infection and others
factors. The microorganisms is very important in the study of
epidemiology that main Endemic -Epidemic infections in
community and concerned with:
1 ) The patterns disease occurrence.
2 ) Communicable disease and identify the causes.
3 ) Studies the reservoir and sources.
4 ) Mode of spread of an infection and route of transmission
of disease .
There are two factors that determinethe frequency of epidemiological
infections in the community :
a - Social factors.
b - Environmental factors.
Uses of Epidemiology: Identifying the reservoir and mode of
transmission of disease agent
Identifying the origin of an epidemic
depends of the characteristic and activity of
those affected and unaffected by the
Worldwide travel and distribution of foods
increase the global threat of disease.
Diseases in which symptomatic humans are
the only reservoir are the easiest to control.
Aims of the study of epidemiology: To describe the state of health in a
community or aggregate.
To understand the use of
epidemiological methods in primary,
secondary and tertiary prevention.
To identify epidemiological study
designs for researching health
Some broad aims and goals of epidemiology are to:1. Determine the primary agent or ascertain causative factors.
2. Understand the causation of disease, disorders, or
3. Determine the characteristics of the agent or causative
4. Define the mode of transmission.
5. Define and determine contributing factors.
6. Identify and explain geographic disease patterns.
7. Determine, describe, and report the natural course of
disease, disability, injury, and death.
8. Determine control methods.
9. Determine preventive measures.
10. Aid in the planning and development of health services.
11. Provide administrative and planning data.
Principles of Epidemiology: Observation of the infection and
community that have infection.
Description of the state.
Collection of data.
Construction on important to deal
In epidemiological studies appear more than one factoraggregate for occurrence of any disease:
Multifactorial causes .The pathogenic microorganisms (microbes) that cause infectious
diseases in human with some factors as for: e.g. TB infection to
microorganisms Tb bacilli
Sun - light and darkness .
Complex Multifactorial causes .
Agent of disease - etiologic factors .
A nthrax Campylobacteriosis
Mad Cow Disease
West Nile Virus
Model of Epidemiology:These factors applied on any disease and
some of studies or reference term this
Triangle other definition Triangle
" Biopsychosocialtheory , other model of the
public health model of addiction as
Epidemiologic triad for cause illness state
that contribute to an illness, injury or
wellness state. Intervention may focus on any
of these three to prevent the spread of illness
or to improve health in a population.
3 ) HostTriangle model
Epidemiologic triadEpidemiologists study the causal
agent, the susceptible host, and
environmental factors that contribute
to an illness, injury, or a wellness
state . Intervention may focus on any
of these three to prevent the spread of
illness or to improve health in a
1 : Agents factors :An agent is a factor that causes or
contributes to a health problem
Causative agents can be factors, e.g.
Bacteria that cause tuberculosis ,
Rocks on a mountain road that
contribute to an automobile crash
factors that are lacking , e.g . lack iron
in the body that causes anemia.
The development of disease isdependent on the extent of exposure or
includes six agents' types :
Nutritive elements agents .
Chemical agents .
Physical agents .
Biologic (Infectious agents) .
Psychological agents .
Genetic agents .
2 : Environment Factors:The an environment refers to all the external
factors surrounding the host that might influence
vulnerability or resistance. Conditions including
the biological social and physical environmental
existing at the time of exposure to agent
includes as factors :
Poverty. Overcrowding. Social factors .
Seasonal factors, Climate. Attitude .
Geography. Weather. Animals
Safety of buildings. Water and food supply.
3 : Host factors:The host is a susceptible human or animal that
harbor and nourishes a disease - causing agent .
Many physical, psychological, and lifestyle
factors influence the host's susceptibility and
response to an agent including :
Genetic, age, sex, race, and ethnic group .
Physiologic state .
Prior immunologic (Immunity) .
Inter current or preexisting disease .
Human behavior .
Constitutional factors .
Host Factors:Host : an organism on or in which smaller organisms or
viruses live feed and reproduce. Any susceptible man or
animal exposed to microorganisms. Intermediate (host, host of
animal). Asexual cycle that depends on:
Demographic data : Age, gender, ethnic background, race
marital status, religion, education and economic status.
Level of health : Genetic risk factor, anatomical factors
response to stress, previous disease, nutrition, fitness,
Body defenses : Resistance and immunity, autoimmune system
Lymphatic system. State of immunity such as susceptibility
versus active or passive immunity.
Human behaviors : Diet, exercise, hygiene, substance abuse
occupation, personal and sexual contact use of health,
resource, food handling.
Spread of Disease :Any disease to spread an infectious
agent must have :
A suitable habitat in it normally lives
and multiplies .
A mode of transmission to the next
An appropriate rote to enter the host .
Chain of events in infectious process:Etiological agent
Portal of exit
Mode of transmission
Portal of entry
Fig 1.2 Chain of events in infectious processModes of Transmission
Incubation PeriodThe period of time after an infection is
established but before the first signs or
Different diseases generally have
different incubation times and
Therefore, can derive epidemic curves
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