concept of health and illness

1. HEALTH
AND
ILLNESS

2. HEALTH
• Health is a complex concept. It is not static. It is multidimensional concept
related to physical, mental, emotional, social, cultural, spiritual and
environmental aspect. Health is a changing, evolving concept that is basic to
nursing.
• Health is a positive concept emphasizing social and personal resources, as well
as physical capacities.
• Optimum health is the highest level of health possible for an individual; the
balance of physical, emotional, social, spiritual and intellectual health.
• The goal of nursing care is to maintain optimum health of the client.

3. Definition of health
• Health is a state of complete physical, mental and social well-being, and not
merely the absence of disease or infirmity. (WHO, 1947)
• Health is not a condition; it is an adjustment; it is not a state but a process. The
process adapts the individual not only to our physical, but also our social
environments. (President Commission, 1953)
• A state of wellbeing in which the person is able to use purposeful, adaptive
responses and processes, physically, mentally, emotionally, spiritually and
socially, in response to internal and external stimuli (stressors) in order to
maintain relative stability and comfort and to strive for personal objectives and
cultural goals. (Murry and Zenter, 1989)

4. Concept of Illness and disease
• Disease is a medical term meaning that there is pathological change is structure
or function of the body or mind. It is a condition that has specific symptoms and
boundaries.
• Illness is individualized perception or experience where one feels a change in
his or her body functioning and which interferes with his or her ability to work
as usual.
• An illness is the response the person has, to a disease, an abnormal process in
which the persons' level of functioning is altered compared to the previous level.
• Illness is not merely absence of diseased. It is a state in which a persons'
physical, developmental or spiritual functioning is impaired compared with that
persons' previous experience.

5. Concept of Illness and disease
• Illness is feeling bad, having distressing symptoms such as pain, and being
unable to carry on daily activities is known as illness.
• Illness refers not only presence of specific disease but also to individual
perception and behavior in response to the disease as well as impact of that
disease on the psychological environment.
• Therefore, illness can be said as a state in which the person feels unhealthy,
experiences disturbances of or failure in bio-psychosocial adaptation.
• During illness person's ability to carryout minimal physical, psychological, or
socially appropriate/ acceptable behavioral expectation to customary role status
is impaired.

6. Concept of wellness and wellbeing
• Wellness is an active dimensional process of becoming aware of making choices
towards higher level of wellbeing.
• Wellness is a developing awareness that there is no end point but that health and
happiness are possible in each moment here and now (Travis and Ryan, 1988).
• Wellness is an active process of becoming aware of and making choices towards
a more successful existence, (National wellness Institute).
• It is a holistic concept, looking at the whole person, not just their blood pressure,
body fat, exercise behavior or what a person had lunch. It involves all possible
dimensions.

7. Models of health
• Agent-Host Environment Model.
• Health Belief Model
• Health Illness Continuum
• Dunn’s High-level Wellness
• Travis’s Illness Wellness Model

8. Agent-host environment model
• Also called the ecological model
• Originated in the community health work of Leavell and Clark (1965)
• This model describes disease or illness as the result of the dynamic interaction
of factors related to agent, host, and environment.
• Because each of agent-host-environment factors constantly interact with the
others, health is an ever changing state.
• When variables are in balance health is maintained; when variables are not in
balance, disease occurs
• The key points of this model are:
• Predicting illness rather than promoting wellness.
• Identification of risk factors.
• Promoting and maintaining health

9. • .
HOST
AGENT ENVIRONMENT
Agent-host environment model

10. • Biological
• micro-organisms
• Physical
• temperature, radiation, trauma, others
• Chemical
• acids, alkalis, poisons, tobacco, others
• Environmental
• nutrients in diet, allergens, others
Agent

11. • Genetic endowment
• Immunologic status
• Individual characteristics
• Individual behavior
host

12. •Living conditions (housing, crowding, water supply,
refuse, sewage, etc)
•Atmosphere / climate
•Modes of communication: phenomena in the
environment that bring host and agent together, such as:
vector, vehicle, reservoir, etc)
environment

13. Health belief model
• Rosen stock proposed a health belief model intended to predict individual would
or not use preventive measure for early detection of cancer.
• Becker modified this model to include the components as individual perception,
modifying factors and variable likely to affect initiating action.
• This model is based on the premise that for a behavioral change to succeed,
individuals must have the incentive to change, feel threatened by their current
behavior, and feel that a change will be beneficial and be at acceptable cost.
• They must also feel competent to implement that change .
• The purpose of the model is to explain and predict preventive health behavior.

14. Health belief model
• Health beliefs are person's ideas convictions and attitudes about health and
illness. These beliefs are based on factual information or misinformation
common sense or myths.
• Because health beliefs usually influence health behaviour, they positively or
negatively affect a patient's level of health.
• Positive health behaviours are activities related to maintaining, attaining or
regaining good health and preventing illness.
• Common positive health behaviours include immunizations, proper sleep
patterns, adequate exercise and good nutrition.

15. Health belief model
• Implementation of the health behavior depend on an individual's awareness of
home to live a healthy life and the person's ability and willingness to carryout
such behavior in a healthy lifestyle.
• Negative health behavior include activities that are actually or potentially
harmful to health, such as smoking drug and alcohol abuse, poor diet and refuse
to take necessary medications or to care for oneself.
• This model is also based on motivational theory and is also based what people
perceive or believe to be true about themselves in relation to health.
• It addresses relationship between a person's beliefs and actions.

16. Health belief model
Individual perception Modifying factors Likelihood of action
Demographic variables
(Age, sex, race, Ethnicity)
Sociopsychological variables
(Personality, social class, peer
and reference group pressure)
Perceived threat of disease
Cues of action
Mass media campaign
Advice from others
Reminder postcard from physician
Illness of family member or friend
Newspaper or magazine article
Perceived benefits of
preventive action minus
perceived barriers to
preventive action
Likelihood of taking
recommended preventive
health action
Perceived susceptibility
to disease
Perceived seriousness
(severity) to disease

17. Individual perception
• Perceived seriousness:
• It is an individual's judgment as to the severity of the disease.
• Perception of seriousness of illness may affect health for example the concern about the
spread of HIV (Human Immunodeficiency Virus) reflects the general public's perception
of seriousness of this illness.
• The probability that a person will change his/her health behaviors to avoid a consequence
depends on how serious he or she considers the consequence to be.

18. Individual preception
• Perceived susceptibility:
• An individual's assessment of his or her chances of getting the disease.
• It is more effective in prompting people to adopt healthier behavior.
• The greater the perceived risk, the greater the likelihood of engaging in behavior to
decrease the risk.
• If mother died by cervical cancer, the daughters are motivated for early pap smear test.
• People will not change their health behaviors unless they believe that they are at risk
• Perceived threat:
• Perceived susceptibility and perceived seriousness combine to determine the total threat
of illness.
• In one area where the incidence is increasing suddenly, normal people may not feel threat
but, if the individual is a drug abuser, or had blood transfusion just last month after
accident, they may perceive more threat.

19. Modifying factors
• Individual's personal factors that affect whether the new behavior is adopted.
• Demographic variables
• like age, gender, race, ethnicity etc
• An infant cannot perceive the importance of balanced diet, an adolescent may perceive
peer approval is more important than family approval and may participate in hazardous
activities or adopt unhealthy lifestyles.
• Structural variables
• like knowledge about the disease, prior contact with the disease presumed to influence
preventive behavior.

20. Modifying factors
• Socio-psychological variables
• like personality, social class, peer and reference group pressure.
• Social pressure or influence from peers or other reference group may encourage
preventive health behaviors even though an individual's motivation is low.
• Expectation of others may motivate people such as no driving after drinking alcohol
• Cues to action:
• Internal cues (feelings of fatigue, uncomfortable) or external cues (advice from others,
news etc.) which is used to determine action.
• It is strategy to activate "readiness", by providing information, promote awareness
through mass media campaigns, advice from other, articles etc.

21. Likelihood to action
• Those factors that will start on the way to changing behaviors.
• Perceived benefit of action:
• An individual's conclusion as to whether the new behavior is better than what he/she is
already doing.
• For example, refraining from smoking to prevent lung cancer.
• It is difficult to convince people to change a behavior if there isn't something in it for
them.
• A man probably will not stop smoking if he doesn't think that doing so will improve his
life in some way.

22. Likelihood to action
• Perceived barrier to action:
• An individual's opinion as to what will stop him/her from adopting the new behaviors
such as cost, inconvenience, unpleasantness and life-style change.
• One of the major reason people do not change their health behaviors is that they think that
doing so is going to be hard.
• Sometimes it is not just a matter of physical difficulty, but social difficulty as well.
• Likelihood of taking recommended preventive health action:
• It is personal belief in one's own ability to do something.
• Cues to action are external events that prompt a desire to make health change.
• A cue to action is something that helps move someone from wanting to make a health
change to making the change

23. Health belief model: conclusion
• The Health Belief Model is based on the understanding that a person will take a
health-related action:
• If he/she feels that a negative health condition can be avoided from example, HIV.
• Has positive expectation that by taking a recommended action, he/she will avoid a
negative health condition for example using condoms will be effective at preventing HIV.
• Believes that he/she can successfully take a recommended health action ie he/she can use
condoms comfortably and confidently.
• Personal beliefs influence health behaviors so the nurse plays a major role in
helping clients implement healthy behaviors.
• They help in client's health monitoring, supplying anticipatory guidance and in
imparting knowledge about health.
• They can also reduce barriers to action and can support positive action.

24. Health continuum model
• Health is a dynamic state that continually change as a person adapts to changes
in the internal and external environment.
• Illness is abnormal process in which functioning of a person is diminished or
impaired in one or more dimensions.
• Health and illness is an interactive continuum with multiple configurations
ranging from depletion health (death) to high level wellness.
• High level wellness is further conceptualized as self-actualization and
maximization of a person's potential. Health illness continuum is a scale by
means of which a person's level of health can be described ranging from high
level wellness to severe illness.
• This scale considers the presence of risk factors.

25. Health continuum model
• The health-illness continuum illustrates this process of change, in which the
individual experiences various states of health and illness (ranging from
extremely good health to death) that fluctuate throughout his life.

26. Health continuum model
• Adaptation and effective functioning, even in the presence of chronic disease,
can be considered a state of wellness.
• A person may be in perfect physical condition but feel too tired to go to work,
while his co-worker, a diabetic, is at work, functioning fully.
• Death occurs when adaptation fails completely, and there is irreversible damage
to the body.
• As health and illness are relative qualities, existing in varying degree or levels, it
is more accurate to consider health and illness in terms of a scale or continuum
rather than as absolute states.
• Continuum models are used to measure a person's perceived level of wellness.

27. Health continuum model
• For example, two students just found out about a big test tomorrow, for which
they are completely unprepared.
• One student responds to this stressful situation (stressor) by going home, getting
his books out, and starting to study.
• The other student breaks out into a sweat and spends most of the evening
fretting over this outrage and imagining what will happen to him if he doesn’t
pass the test.
• No doubt, this student is doing more damage to his health than is his friend.
• And, considering the time and energy he is expending on worrying (and not
studying), he may experience even more stress when they receive their grades!
• Adaptation and effective functio

28. Travis illness-wellness continuum
• It is used to measure person's perceived level of wellness.
• According to Travi's illness and wellness continuum, the two arrows pointing in
opposite directions and joined at a neutral point indicates the point of person's
perceived level of wellness.
• Most importantly, what is to be considered in this continuum is the direction an
individual is facing on pathway.
• If towards premature death, person is pessimistic and negative outlook.
• If towards high level health, person is optimistic and positive outlook.

29. Travis illness-wellness continuum
• Components
• Movement to the right indicates increasing level of health and wellness. This is
achieved in 3 steps: awareness, education, and growth.
• Movement to the left indicates progressively decreasing state of health. This is
achieved in 3 steps: signs, symptoms, and disability.

30. .
• Comparing treatment model with wellness model:
• If treatment model is only used - Individual can move only up to the neutral
point for example, hypertensive patient who is only under medication without
making any life style changes.
• If wellness model is used - Individual can move right part the neutral point. E.g.
Hypertensive patient who not only takes medicine but also quits smoking, loses
weight, makes dietary modification etc Wellness model and treatment model can
work together. This model shows it is possible to be physically ill and at the
same time oriented towards wellness.

31. Dunn’s high level wellness grid
• Dunn defines ‘Health-illness continuum’
on gradual scale in which each person
has neither absolute health or illness but
it is relative and ever-changing state of
being ranging from peak of ‘high level
of wellness to extreme poor health and
death.
• It demonstrate interaction of
environment with illness-wellness
continuum

32. Components of Dunn’s high level wellness grid
• Two Axes
• Health axis: It extends from peak wellness to death
• Environment axis: it extends from very favorable environment to very unfavorable environment
• Four quadrants:
• High level wellness in favorable environment: Example, a person who implements healthy lifestyle
behaviors and has the bio-psychological, spiritual and economic resources to support this lifestyle
• Emergent high-level wellness in unfavorable environment: Example, one who has knowledge to
implement healthy practices but doesn't implement adequate self care practices because of various
obstacles
• Protected poor health in favorable environment: Example, an ill person whose needs are met by the
health care system and has access to appropriate medications, diet and health care instructions
• Poor health in unfavorable environment: Example, a young child starving in drought-stricken country

33. Five premises of high level wellness in Dunn’s model
• Totality: integration of physical, physiological, physiological, psychological
concepts into unified whole
• Uniqueness: regarding totality, one component of individual must be viewed in
contest of another component. Separation of these, in fail to recognize the total
interdependency of one with others crate change in another.
• Energy: same energy may be beneficial for one person and destructive for other
• Inner and Outer World: the interaction of individual with extreme environment
is a reflection of his/her present and past experience (Inner world)
• Self integration and energy use: person’s physical, physical, psychological
components must be integrated. If changes occurs in one of these components, the
person must learn new pattern of integration to restore or maintain high level wellness.

34. Stages of illness
• Transition from health to illness
• Acceptance of illness
• Convalescence

35. TRANSITION FROM HEALTH TO ILLNESS
• This stage starts when person considers that he/she might be ill and ends when
others acknowledge that the person is ill.
• Illness may begin with vague, nonspecific symptoms that a person initially
attempts to deny.
• The symptom is a subjective indication of organic or psychic malfunctioning or
a change in person's condition that indicates some physical or mental state of
disease.
• When a symptom persists, a person may seek medical consultation but still not
admit to being ill.

36. TRANSITION FROM HEALTH TO ILLNESS
• If illness occurs a sudden crisis, the person my fear that the medical help will be
either incompetent Or not immediately available.
• Therapeutic interaction with the ill person and significant others is important
through the stage of transition.
• Shock, disbelief, and denial will probably feel by the patient as well as
significant others.
• Recognition of symptoms(unpleasant sensation)-
• Pain, fever, rashes, indigestions etc.
• Loss of energy/ stamina or feeling of weakness
• Decreased ability to function.
• Fear of diagnosis or treatment.

37. Acceptance of illness
• This stage occurs as the person stops denying illness and takes on a sick role.
• This stage may be a tie of considerable physiologic and psychological
dependence, when the ill person becomes unusually focused on the self.
• This self-centeredness may considered a positive response in that the body is
permitted to concentrate energy on healing and recovery.
• During illness the person may go through a mourning process for loss of body
function prior structure, even if such loss is temporary.

38. Acceptance of illness
• Defines himself/herself as being sick.
• Seeks validation of this experience from others. ‹ up normal activities and
assumes sick role.
• On the basis if health belief and practice the person may choose to do nothing,
takes medication to relieve symptoms and seeks medical care.
• Expresses anger, guilt towards own illness.
• Accepts the diagnosis and Increases dependency.
• Convalescence is the gradual recovery of health and strength after illness or injury.
• It refers to the later stage of an infectious disease or illness when the patient
recovers and returns to normal but may continue to be a source of infection even if
feeling better.

39. convalescence
• In this sense, "recovery" can be considered a synonymous term.
• This also sometimes includes patient care after a major surgery, under which they
are required to visit the doctor for regular check-ups.
• The person reassessing the meaning of life and is becoming independent, stable,
outward looking and involved in decision making.
• Recovery and rehabilitation
• Gives up dependent role
• Resumes normal activities and responsibilities

40. Tasks of convalescence
• Reassessment of life’s meaning
• This is one of the primary task where client redefines meaning of life and tries to set a goal for
maximum productive potential for daily life.
• Reintegration of body image
• This is successful adaptation stage in which the client accepts his new body image positevily,
especially in the acute phase of illness when the patient is less concerned about any threat of
life. It depends upon functions and significance of part of body e.g. amputation.
• Resolution of role change:
• The client role change may depend upon the severity of illness that influence the client self,
family and society. The client may assume sick role, dependent role or independent role.

41. Eleven stages of illness

42. CONCEPT OF
DISEASE

43. iNTRODUCTION
• Upto the time of Louis Pasteur (1922-1895), various concepts of disease
causation were in vogue
• the supernatural theory of disease,
• the theory of humors,
• the concept of contagion,
• miasmatic theory of disease,
• the theory of spontaneous generation, etc.
• Discoveries in microbiology marked a turning point in our etiological concepts.

44. GERM THEORY OF DISEASE
• This concept gained momentum during the 19th and the early part of 20th
century.
• The emphasis had shifted from empirical causes (e.g. , bad air) to microbes as
the sole cause of disease.
• The concept of cause embodied in the germ theory of disease is generally
referred to as a one-to-one relationship between causal agent and disease.
• The disease model accordingly is :
Disease agent Man Disease

45. GERM THEORY OF DISEASE
• The germ theory of disease, though it was a revolutionary concept, led many
epidemiologists to take one-sided view of disease causation.
• That is, they could not think beyond the germ theory of disease.
• It is now recognized that a disease is rarely caused by a single agent alone, but
rather depends upon several factors which contribute to its occurrence.
• Therefore, modern medicine has moved away from the strict adherence to the
germ theory of disease.

46. Epidemiological triad
HOST
AGENT ENVIRONMENT
Time

47. Epidemiological triad
• The germ theory of disease has many limitations.
• For example, it is well-known, that not everyone exposed to tuberculosis develops
tuberculosis.
• The same exposure, however, in an undernourished or otherwise susceptible person may
result in clinical disease.
• Not everyone exposed to beta-haemolytic streptococci develops acute rheumatic fever.
• There are other factors relating to the host and environment which are equally
important to determine whether disease will occur in the exposed host.
• This demanded a broader concept of disease causation that synthesized the basic
factors of agent, host and environment.

48. Epidemiological triad
• This triangle is based on the communicable disease model and is useful in
showing the interaction and interdependence of agent, host, environment, and
time as used in the investigation of diseases and epidemics.
• The agent is the cause of disease;
• the host is an organism, usually a human or an animal, that harbours the disease,
• the environment is those surroundings and conditions external to the human or animal that
cause or allow disease transmission
• time accounts for incubation periods, life expectancy of the host or the pathogen, and
duration of the course of illness or condition.

49. Agents
• Biological agents
• These are living agents of disease, viz, viruses, rickettsiae, fungi , bacteria, protozoa and
metazoa.
• These agents exhibit certain "host- related" biological properties such as:
• Infectivity: this is the ability of an infectious agent to invade and multiply (produce
infection) in a host;
• Pathogenicity: this is the ability to induce clinically apparent illness, and
• Virulence : this is defined as the proportion of clinical cases resulting in severe clinical
manifestations (including sequelae} The case fatality rate is one way of measuring
virulence

50. Agents
• Nutrient agents
• These are proteins, fats, carbohydrates, vitamins, minerals and water.
• Any excess or deficiency of the intake of nutritive elements may result in nutritional
disorders.
• Protein energy malnutrition (PEM), anaemia, goitre, obesity and vitamin deficiencies are
some of the current nutritional problems in many countries.
• Chemical agents
• Endogenous: Some of the chemicals may be produced in the body as a result of
derangement of function, e.g., urea (ureamia), serum bilirubin (jaundice), ketones
(ketosis}, uric acid (gout}, calcium carbonate (kidney stones), etc.
• (ii) Exogenous: Agents arising outside of human host, e.g. , allergens, metals, fumes, dust,
gases, insecticides, etc. These may be acquired by inhalation, ingestion or inoculation.

51. Agents
• Physical agents
• Exposure to excessive heat, cold, humidity, pressure, radiation, electricity, sound, etc may
result in illness.
• Mechanical agents
• Exposure to chronic friction and other mechanical forces may result in crushing, tearing,
sprains, dislocations and even death.
• Social agents
• It is also necessary to consider social agents of disease.
• These are poverty, smoking, abuse of drugs and a lcohol, unhealthy lifestyles, social
isolation, maternal deprivation etc.

52. Agents
• Absence or insufficiency or excess of a factor necessary to health
• Chemical factors : e.g., hormones {insulin, oestrogens, enzymes)
• Nutrient factors
• Lack of structure: e.g., thymus
• Lack of part of structure, e.g., cardiac defects
• Chromosomal factors, e.g., mongolism, turner's syndrome,
• Immunological factors, e.g., agammaglobulinaemia.

53. Host Factors
• Genetic endowment
• Immunologic status
• Individual characteristics
• Individual behavior
• Definitive versus intermediate (in vector-borne diseases)

54. Host Factors
• In epidemiological terminology, the human host is referred to as "soil" and the
disease agent as "seed".
• In some situations, host factors play a major role in determining the outcome of
an individual's exposure to infection (e.g., tuberculosis).
• The host factors may be classified as
• Demographic characteristics such as age, sex, ethnicity
• Biological characteristics such as genetic factors; biochemical levels of the blood (e.g.,
cholesterol); blood groups and enzymes; cellular constituents of the blood; immunological
factors; and physiological function of different organ systems of the body (e.g., blood
pressure, forced expiratory ventilation). etc.
• Social and economic characteristics such as socioeconomic status, education,
occupation, stress, marital status, housing, etc.
• Lifestyle factors such as personality traits, living habits, nutrition, physical exercise, use
of alcohol, drugs and smoking, behavioural patterns, etc.

55. Environment
• Living conditions (housing, crowding, water supply, refuse, sewage, etc)
• Atmosphere / climate
• Modes of communication: phenomena in the environment that bring host and
agent together, such as: vector, vehicle, reservoir, etc)

56. Environment
• Physical environment
• The term "physical environment" is applied to non-living things and physical factors (e.g.,
air, water, soil, housing, climate, geography, heat, light, noise, debris, radiation, etc) with
which man is in constant interaction.
• Man's victory over his physical environment has been responsible for most of the
improvement in health during the past century.
• Man has altered practically everything in his physical environment to his advantage.
• In doing so, he has createor himself a host of new health problems such as air pollution,
water pollution, noise pollution , urbanization, radiation hazards, etc.
• The increasing use of electrical and electronic devices, including the rapid growth of
telecommunication system (e.g., satellite systems), radiobroadcasting, television
transmitters and radar installations have increased the possibility of human exposure to
electromagnetic energy.

57. Environment
• Biological environment
• The biological environment is the universe of living things which surrounds man,
including man himself.
• The living things are the viruses and other microbial agents, insects, rodents, animals and
plants.
• These are constantly working for their survival, and in this process, some of them act as
disease- producing
• Psychosocial factors can also affect negatively man's agents, reservoirs of infection
,intermediate hosts and vectors of disease.
• Between the members of the ecological system (which includes man) there is constant
adjustment and readjustment.
• For the most part, the parties manage to effect a harmonious interrelationship, to achieve a

58. Environment
• Biological environment
•The biological environment is the universe of living things which surrounds man, including man.
•The living things are the viruses and other microbial agents, insects, rodents, animals and plants.
•These are constantly working for their survival, and in this process, some of them act as disease-
producing agents, reservoirs of infection, immediate hosts and vectors of diseases
•Between the members of the ecological system (which includes man) there is constant
adjustment and readjustment.
•For the most part, the parties manage to effect a harmonious interrelationship, to achieve a state
of peaceful co-existence, even though this may not be always enduring.
• When for any reason, this harmonious relationship is disturbed, ill-health results.
•In the area of biological environment also, preventive medicine has been highly successful in
protecting the health of the individual and of the community.

59. Environment
• Psychosocial environment
• It is difficult to define "psychosocial environment" against the background of the highly
varied social, economic and cultural contexts of different countries and their social
standards and value systems.
• It includes a complex of psychosocial factors which are defined as "those factors affecting
personal health, health care and community wellbeing that stem from the psychosocial
make-up of individuals and the structure and functions of social groups"
• They include cultural values, customs, habits, beliefs, attitudes, morals, religion,
education, lifestyles, community life, health services, social and political organization.
• The impact of social environment has both positive and negative aspects on the health of
individuals and communities.

60. Multifactorial causation
• The concept that disease is due to multiple factors is not a new one.
• Pettenkofer of Munich (1819- 1901) was an earlyproponent of this concept.
• But the "germ theory of disease" or "single cause idea" in the late 19th century
over-shadowed the multiple cause theory.
• Epidemiology has contributed significantly to our present day understanding of
multifactorial causation of disease.
• Medical men are looking "beyond the "germ theory" of disease into the total life
situation of patient & community in search of multiple (or risk) factors of
disease.

61. Multifactorial causation
• The advanced model of the triangle of epidemiology includes all facets of the
communicable disease model, and to make it more relevant and useful regarding
today's diseases, conditions, disorders, defects, injuries, and deaths.
• It also reflects the causes of current illnesses and conditions.
• Behavior, lifestyle factors, environmental causes, ecologic elements, physical
factors, and chronic diseases must also be considered.
• The term agent is replaced by causative factors, which implies the need to identify
multiple causes or an etiologic factors of disease, disability, injury and death.
• The purpose of knowing the multiple factors of disease is to quantify and prioritize
sequentially for modification or amelioration to prevent or control disease.
• It offers multiple approaches for the prevention/control of disease.

62. Multifactorial causation
Causative factors
Groups or
population
and their
characteristics
Environment
behavior, culture,
physiological
factors, ecological
elements
Time

63. Web of causation
• This model of disease causation was suggested by MacMahon and Pugh in their
book: "Epidemiologic Principles and Methods" .
• This model is ideally suited in the study of chronic disease, where the disease
agent is often not known, but is the outcome of interaction of multiple factors.
• The "web of causation" considers all the predisposing factors of any type and
their complex interrelationship with each other.
• The basic tenet of epidemiology is to study the clusters of causes and
combinations of effects and how they relate to each other.
• The causal web provides a model which shows a variety of possible interventions
that could be taken which might reduce the occurrence of disease or condition.

64. Web of causation
• The web of causation does not imply that the disease cannot be controlled
unless all the multiple causes or chains of causation or at least several of them
are appropriately controlled or removed.
• Sometimes removal or elimination of just only one link or chain may be
sufficient to control disease, provided that link is sufficiently important in the
pathogenetic process .
• In a multifactorial event, therefore , individual factors are by no means all of
equal weight.
• The relative importance of these factors may be expressed in terms of "relative
risk"

65. Web of causation
Example: Myocardial infarction
Web of causation

66. Natural history of diseases.
• Disease results from a complex interaction between man, an age nt (or cause of
disease) and the environment.
• The term natural history of disease is a key concept in epidemiology.
• It signifies the way in which a disease evolves over time from the earliest stage of
its pre-pathogenesis phase to its termination as recovery, disability or death, in the
absence of treatment or prevention.
• Each disease has its own unique natural history, which is not necessarily the same
in all individuals
• What the physician sees is just an "episode" in the natural history of disease.
• Understanding about it is based on cohort and epidemiological studies.
• Important to understand chain of events and application of preventive measures.

67. Natural history of diseases

68. Pre pathogenesis phase
• This refers to the period preliminary to the
onset of disease in man.
• The disease agent has not yet entered man,
but the factors which favour its interaction
with the human host are already existing in
the environment.
• This situation is frequently referred to as
"man in the midst of disease" or "man
exposed to the risk of disease".
• Potentially we are all in the prepathogenesis
phase of many diseases, both communicable
and non-communicable.

69. Pre pathogenesis phase
• The causative factors of disease may be classified as AGENT, HOST and
ENVIRONMENT.
• These three factors are referred to as epidemiological triad.
• The mere presence of agent, host and favourable environmental factors in the
prepathogenesis period is not sufficient to start the disease in man.
• What is required is an interaction of these three factors to initiate the disease
process in man.
• The agent, host and environment operating in combination determine not only
the onset of disease which may range from a single case to epidemics but also
the distribution of disease in the community.

70. Pathogenesis phase
• The pathogenesis phase begins with the entry of the disease "agent" in the susceptible
human host.
• The further events in the pathogenesis phase are clear-cut in infectious diseases, i.e.,
the disease agent multiplies and induces tissue and physiological changes, the disease
progresses through a period of incubation and later through early and late
pathogenesis.
• The final outcome of the disease may be recovery, disability or death.
• The pathogenesis phase may be modified by intervention measures such as
immunization and chemotherapy.
• At this stage that the host’s Epidemiologic concept of interactions of Agent, Host and
Environment reaction to infection with a disease agent is not predictable.

71. Pathogenesis phase
• That is, the infection may be clinical or subclinical; typical or atypical or the host
may become a carrier with or without having developed clinical disease as in the
case of diphtheria and hepatitis B.
• In chronic diseases (e.g. , coronary heart disease, hypertension, cancer), the early
pathogenesis phase is less dramatic. This phase in chronic diseases is referred to
as presymptomatic phase.
• During the presymptomatic stage, there is no manifest disease.
• The pathological changes are essentially below the level of the "clinical horizon".
The clinical stage begins when recognizable signs or symptoms appear.
• By the time signs and symptoms appear, the disease phase is already well
advanced into the late pathogenesis phase. In many chronic diseases, the agent-
host-environmental interactions are not yet well understood.

72. Iceberg concept of disease
• A concept closely related to the spectrum of disease is the concept of the
iceberg phenomenon of disease.
• According to this concept, disease in a community may be compared with an
iceberg
• The floating tip of the iceberg represents what the physician sees in the
community, i.e., clinical cases.
• The vast submerged portion of the iceberg represents the hidden mass of
disease, i.e. , latent, inapparent, presymptomatic and undiagnosed cases and
carriers in the community.
• The "waterline" represents the demarcation between apparent and inapparent
disease.

73. Iceberg concept of disease

74. Iceberg concept of disease
• In some diseases (e.g., hypertension, diabetes, anaemia, malnutrition, mental
illness) the unknown morbidity (i.e., the submerged portion of the iceberg) far
exceeds the known morbidity.
• The hidden part of the iceberg thus constitutes an important, undiagnosed
reservoir of infection or disease in the community, and its detection and control
is a challenge to modern techniques in preventive medicine.
• One of the major deterrents in the study of chronic diseases of unknown
etiology is the absence of methods to detect the subclinical state - the bottom of
the iceberg

75. Dynamics of disease transmission
• Communicable diseases are transmitted from the reservoir/source of infection
to susceptible host.
• Basically, there are three links in the chain of transmission, viz, the reservoir,
modes of transmission and the susceptible host.

76. Sources or reservoir
• The starting point for the occurrence of a communicable disease is the
existence of a reservoir or source of infection.
• The source of infection is defined as "the person, animal, object or substance
from which an infectious agent passes or is disseminated to the host“.
• A reservoir is defined as any person, animal, arthropod, plant, soil or substance
(or combination) in which an infectious agent lives and multiplies, on which it
depends primarily for survival, and where it reproduces itself in such manner
that it can be transmitted to a susceptible host.
• In short, the reservoir is the natural habitat in which the organism metabolizes
and replicates.

77. Sources or reservoir
• The terms reservoir and source are not always synonymous.
• In hookworm infection, the reservoir is man, but the source of infection is the soil
contaminated with infective larvae.
• In tetanus, the reservoir and source are the same, that is soil. In typhoid fever, the
reservoir of infection may be a case or carrier, but the source of infection may be faeces
or urine of patients or contaminated food, milk or water.
• The term homologous reservoir is applied when another member of the same
species is the victim, e.g., vibrio cholerae in man
• The term heterologous is applied when the infection is derived from a reservoir
other than man, as for example animals and birds infected with salmonella.
• The reservoir may be of three types:
• Human reservoir,
• Animal reservoir
• reservoir in non-living things

78. Modes of transmission
• Communicable diseases may be transmitted from the reservoir or source of
infection to a susceptible individual in many different ways, depending upon
the infectious agent, portal of entry and the local ecological conditions.
• As a rule, an infectious disease is transmitted by only one route, e.g., typhoid
fever by vehicle transmission and common cold by direct contact.
• But there are others which may be transmitted by several routes e.g., AIDS,
salmonellosis, hepatitis B, b1rucellosis, Q fever, tularemia etc.
• The multiple transmission iroutes enhance the survival of the infectious agent.
• The mode of transmission of infectious diseases may be classified as:
• Direct transmission
• Indirect transmission

79. Modes of transmission
• DIRECT TRANSMISSION
• Direct contact
• Droplet infection
• Contact with soil
• Inoculation into skin or mucosa
• Transplacental (vertical).
• INDIRECT TRANSMISSION
• Vehicle-borne
• Vector-borne
• Mechanical
• Biological
• Air-borne
• Droplet nuclei
• Dust
• Fomite-borne
• Unclean hands and fingers

80. Susceptible host
• First, the infectious agent must find a PORTAL OF ENTRY by which it may
enter the host. There are many portals of entry, e.g., respiratory tract,
alimentary tract, genitourinary tract, skin, etc. Some organisms may have more
than one portal of entry, e.g., hepatitis B, Q fever, brucellosis
• On gaining entry into the host, the organisms must reach the appropriate tissue
or "SITE OF ELECTION" in the body of the host where it may find optimum
conditions for its multiplication and survival.
• Thirdly, the disease agent must find a way out of the body (PORTAL OF EXIT)
in order that it may reach a new host and propagate its species.
• After leaving the human body, the organism must survive in the external
environment for sufficient period till a new host is found.

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