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Epidemiology of population health
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Community health nursing
Lecture (3)
The epidemiology of population
health
Presented to:
Prof. Nawal Soliman
Presentedby:
Fatma Ibrahim Abdel-latif Megahed
2013
Suez CanalUniversity
Faculty of nursing
Community health nursing
Department
Specialtyof master

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Learning Objectives:
At the end of this lecture each student will be able to:-
1. Define epidemiology.
2. List aims of epidemiology.
3. Identify uses of epidemiology.
4. Identify important definitions in epidemiology.
5. Identify the epidemiologic traid.
6. Identify the natural history of disease.
7. Define population health.
8. Identify the characteristics of healthy populations.
9. Discuss factors affecting the health of population.
10. Discuss level of prevention.

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 Introduction:
Epidemiology is the study of health and disease in population. It is a basic toolin public
health and preventive medicine. It is derived from the Greek words. Epi= upon, demos=
people and logus= science. It was originally applied to the study of the epidemics of acute
infectious diseases and was defined as the science of epidemics. Nowadays, it was expanded
to include other health states and phenomena as non-infectious disease such as hypertension,
diabetes, cancer and renal diseases. The goal of public health epidemiology is to help
communities understand more about the experience of health and illness in that population
so that steps can be taken to prevent disease and promote the population health. Healthy
population provides their members with the knowledge and opportunities to make choices
that improve health.
 Definition of the epidemiology:
It is the study of the distribution, dynamics and determinants of health related states and
events in a defined population.
 Distribution includes the description of the disease frequency by place, time and
person.
 Dynamics means the interaction between different factors in transmission of
diseases.
 Determinants are factors that determine the probability of occurrence of disease i.e.
risk factors.
 Aims of population of epidemiology:
1. To describe health status of population.
2. To explain the etiology of disease by identifying factors related to it.
3. To predict the expected number of disease occurrences in population.
4. To control the distribution of disease in population.

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 Uses of epidemiology:
1. Study the etiology of disease and identifying risk factors of a disease.
2. Syndrome identification and describing the natural history of a disease by observing
frequently associated findings in individual patients, e.g., AIDS.
3. Identify the factors or conditions that can be modified to prevent the occurrence or spread
of the disease. Epidemiological studies have been used to test the effectiveness of
vaccination, mass treatment, and health education as measures to prevent spread of the
disease among population.
4. Identifying the health needs of the community e.g. needs to combat poliomyelitis, and
needs for family planning by studying the frequency of diseases and the time.
5. Measure trends (i.e. change of disease pattern by time, whether the disease is propagating
or diminishing).
 Important definitions in epidemiology:
Health: It is a state of complete physical, mental, and social well-being and not merely an
absence of disease or infirmity.
Infection: The entry and development or multiplication of an infectious agent in the body of
man.
Endemic: (En = in, demos = people). It refers to the constant presence of a disease within a
given geographical area or population.
Epidemic: (Epi = upon, Demos = people). It refers to the occurrence of a disease in the
community in excess number of cases more than expected. The “expected number” of cases
to be compared with what is reported in the specified location and during the specified period
of time during the past years.
Outbreak: Is used when the epidemic occurs in small confined area, e.g. school, camp,
hospital, hotel, or prison.
Pandemic: an epidemic affecting more than one country, e.g. H1N1 in 2009.
Zoonosis: an infectious disease transmitted from animals to man, e.g. plague.

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Communicable disease: an illness due to a specific infectious agent or its toxic products,
capable of being directly or indirectly transmitted from man to man.
 The epidemiologic traid:
It is a triangle explaining the interaction between the three elements for the disease occurrence.
For a disease to occur a harmful agent should come into contact with a susceptible host under
specified environment condition.
1. Agent factors: As biological, physical, chemical, nutritive agents ……etc.
2. Host factors (intrinsic): The host factors include: A) biologic traits such as age,
sex, ethnic group, race, and any other genetically determined variable as blood
group. B) Social traits which include occupation, education, marital status, diet,
smoking, drug abuse, and exercise.
3. Environmental factors (extrinsic): The environmental factors include: A)
physical environment (climate, pollution of air or water….etc.). B) Biological
environment (presence of the vector of the disease as mosquitos). C) Social
environment (overcrowding, poverty, dietary habits).
Epidemiological traid
Agent
factors
Host
factors
Environm
ental
factors

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 The natural history of disease:
It refers to the course of disease overtime, unaffected by treatment. Each disease has its own
natural history, which occurs through a sequence of stages:
Stage of susceptibility:
During this stage, the disease has not developed, but the presence of risk factors favor its
occurrence.
Stage of pre-symptomatic disease
During this stage, the disease process has begun, but there are no detectable symptoms.
Recognizable symptoms occur during this stage of disease. This stage is often subdivided
further for better case management and epidemiologic studies.
Stage of disability
Some diseases resolve completely and do not reach this stage. However, there are a
number of conditions that leave a person temporarily disabled.
 Definition of the population health:
* It can be defined as the attainment of the greatest possible biological, psychological and
social well-being of the population as an entity and its individual members. Health is derived
from opportunities and choices provided to the public as well as the population’s response to
those choices (Wilcox & Knapp, 2000).
 The characteristics of healthy populations:
 Foster dialogue among residents to develop a shared vision for the community.
 Promote community leadership that fosters collaboration and partnerships.
 Engage in action based on a shared vision of the community.
 Embrace diversity among residents.
 Asses both needs and assets.
 Link residents to community resources, and
 Foster a sense of responsibility and cohesion among residents (Norris & Pittman, 2000).
Other characteristics of healthy communities include abilities to change and adapt to changing
circumstances and manage conflict effectively.

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 Factors affecting the health of population:
1. Biophysical factors: The human biological factors influencing a population’s health
reflect specific physical attributes of its members. These attributes are; age, genetic
inheritance (gender), race, physiological function and immunity.
2. Psychological factors: The psychological environment influences the health of the
population by increasing or decreasing exposure to stress and affects the ability of the
population to function effectively. These factors include: the future prospects of the
community, significant events in the population’s history& the response to those events,
communication networks existing within the population, evidence of psychological
problems such as suicide & homicide rates and the adequacy of protective services.
3. Physical Environmental factors: Physical environmental factors affecting a
population include: Location, type, climate, physical geography, size, housing, water
supply, and nuisance.
4. Sociocultural factors: Social & cultural factors influence the psychological dimension
and have other effects on health as well. They include information about community
government and leadership, income, occupation, education level, religion, and marital
status.

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5. Behavioral factors: Behavioral factors influence the health status of a population and
its members. These factors include: consumption patterns, and leisure activities.
6. Health system factors: Health care system factors can affect the health of population.
Thus factors include: level of performance, types of health care services, financing of
health care, and community definitions of health & illness.
 The level of prevention:
Prevention strategies are made up of measures that protect people from disease and take the
form of efforts that we use to protect ourselves and others from specific diseases and
conditions and their resulting consequences. There are three levels of prevention: primary,
secondary, and tertiary. Nurses in all settings use all three levels of prevention as a basis for
practice.
1. Primary prevention:
It includes actions taken prior to the onset of disease, which remove the possibility that a
disease will ever occur. It may be accomplished by measures designed to promote general
health and well-being, and quality of life of people or by specific protective measures. The
main components of primary prevention are:
a) Health promotion: It is the process of enabling people to increase control over and to
improve health. It is not directed against any particular disease, but is intended to
strengthen the host through a variety of approaches such as:
 Health education: with the aim of changing the knowledge, attitudes, and practices of
individuals (behavior and lifestyles).
 Environmental modifications: provision of safe water, control of insects, and
improvement of housing.
 Nutritional intervention: child feeding programs, nutrition education.

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b) Specific protection:
 Immunization against infectious diseases.
 Chemo-prophylaxis.
 Protection against occupational hazards.
 Avoiding exposure to specific risk factors e.g. allergens.
2. Secondary prevention: It includes actions at its early stage that delay the progress
of the disease and prevent complications. The specific interventions are :
 Early detection (diagnosis): e.g. screening tests, case finding programs.
 Adequate treatment: It may take the form of mass treatment which is used in the
control of certain diseases, e.g. Bilhariaziasis, Filariasis to interrupt disease
transmission.
Mass treatment may be:
Total Mass treatment selective mass treatment
3. Tertiary prevention: It includes all measures available to reduce or limit
impairments and disabilities, as treatment of complications and rehabilitation.
a) Impairment: is defined as “any loss or abnormality of psychological, physiological
or anatomical structure or function” e.g. loss of foot.
b) Disability: because of an impairment, the affected person may be unable to carry out
certain activities considered normal for his age, sex etc.; loss of foot limiting
walking ability.

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c) Handicap: represents the social impact of disability and the individual is not able to
fulfill his obligations and to play the role expected from him in society e.g.
unemployment.
4. Primordial prevention: Intervention at the most distal point in the chain of
causality. The most distal point are likely to be the political context in which
determinants are operative, followed by aspects of policy (health, social, and
environment), followed by the context of social as well as medical contacts in
communities, followed by individual social and behavioral characteristics (such as
social isolation and health behaviors), followed by physiological states such as related
to perceived stressors.
It occurs when there is focus on a more antecedent primary prevention strategy.
NB.The most effective prevention focuses on the weakest part of the web of interactions
(chain of causality) and not necessary on the most proximal.
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