concept of disease

CONCEPT OF DISEASE

• A condition of the body or some part or organ of the body in which its functions are deranged.

• It is a mal-adjustment of human organism to the environment.

• I t is deviation from normal function.

CONCEPT OF CAUSATION

• DEMONISTIC THEORY• DEVILISITIC THEORY• TRIDOSHAS THEORY• FOUR HUMOURS THEORY• YANG and YIN Principles• GERM THEORY - Louis Pasteur, Robert Koch• EPIDEMIOLOGICAL TRIAD• MULTI FACTORIAL THORY – Web of disease

causation, Wheel of causation

Henle-Koch’s Postulates

1. The agent should be present in every case of the disease under appropriate condition

2. The agent should not be present in any other disease as a fortuitous and Non-Pathogenic agent

3. The agent must be isolated from the body of the individual in pure culture

4. It should induce disease in a new susceptible experiment animal

NATURAL HISTORY OF DISEASE

• IT IS THE WAY IN WHICH A DISEASE EVOLVES OVER TIME FROM THE EARLIEST STAGE OF ITS PREPATHOGENESIS PHASE TO ITS TERMINATION AS RECOVERY, DISABILITY OR DEATH, IN THE ABSENCE OF TREATMENT OR PREVENTION

NATURAL HISTORY OF DISEASE

• PRE-PATHOGENIC PHASE OR SUSCEPTIBILITY STAGE

• PATHOGENIC PHASE1. INCUPATION PERIOD

2. PRODROMAL STAGE

3. STAGE OF OVERT DISEASE

4. STAGE OF DEFERVESCENCE

5. STAGE OF CONVALESCENCE

FACTORS AFFECTING THE GRADIENT OF INFECTION

• Infectivity• Pathogenicity• Virulence• Antigenicity

TYPE OF INFECTION

• Latent infection• Sub-clinical infection or

inapparent or occult• Atypical infection• Severe clinical infection

Factors for development or spread of infectious disease

• An etiological agent responsible for the disease should be present

• There should be a reservoir or carrier for the etiological agent to survive

• The infecting agent should be able to escape from the reservoir of infection through the portal of exit

• There should be a possible source of entry to transmit the agent to a new susceptible host

• The agent should be able to invade the new host• The host should be susceptible

Background

• Infectious disease epidemiology– the occurrence of infectious disease in a given host is dependent

on the presence of disease in other members of the population and the length of time that infected hosts are able to transmit disease to others

– understanding these characteristics of a disease allow us to develop rational measures to control disease

Definition & Stages

• Definition ; The course of a disease from onset (inception) to resolution.

• Stages

Stage of pathologic

onset

Pre-symptomatic stage

Clinically manifest disease

Progress to a fatal termination

Remission and relapses

Regress spontaneously, leading to recovery

Risk Factors Precursors Effect of Treatment Prognostic factor

Risk factor• Risk factor; An aspect of personal behavior or life style, an

environmental exposure, or an inborn or inherited characteristic, that, in the basis of epidemiologic evidence, is known to be associated with health-related condition (s) considered important to prevent.– Risk marker; increased probability of a specified outcome;

not necessarily a causal factor– Determinant; can be modified by intervention, thereby

reducing the probability of occurrence of disease or other specified outcomes

(A) (P) (S) (M) (D) (T)

The Natural history of disease in a patient

• A ; Biologic onset of disease• P ; Pathologic evidence of disease if Sought• S ; Signs and symptoms of disease• M ; Medical care sought• D ; Diagnosis• T ; Treatment

Preclinical Phase Clinical Phase

Gordis L. Epidemiology. WB Saunders Company. 1996

THE NATURAL HISTORY OF A DISEASE

STIMULUS to the HOST

HOST REACTION RECOVERY

interrelation of Agent, Host and Environmental

factors

Latent Period (Pre-symptomatic)

Symptoms, Signs(Clinical)

with or without Defects, Disability

PREPATHOGENESIS

PERIOD OF PATHOGENESIS

Health PromotionSpecific

ProtectionEarly Diagnosis and Prompt

Treatment,

Disability Limitation

Rehabilitation

PRIMARY PREVENTION

SECONDARY PREVENTION

TREATMENT TERTIARY PREVENTION

(Leavell's Level of Application of Preventive Medicine)

Susceptible

host

TIME

Incubation period

Death

Recovery

Exposure Onset

Latent Infectious Non-infectious

Infection

No infection

Clinical disease

• Latent periodthe time interval from infection to development of infectiousness

• Infectious periodthe time during which time the host can infect another susceptible host

• Non-infectious periodthe period when the host’s ability to transmit disease to other hosts ceases

• Incubation periodthe time interval between infection to development of clinical disease

• e.g : Chicken pox– an infectious disease caused by the varicella-

zoster virus – the latent period for chicken pox is shorter than

the incubation period, so a child with chicken pox becomes infectious to others before developing symptoms

Susceptible

host

TIME

Incubation period

Death

Recovery

Exposure Onset

Latent Infectious Non-infectious

Infection

No infection

Clinical disease

• Other examples?– HIV (AIDS)

• latent period relatively short• infectious period occurs (many years) before the onset

of symptoms

Susceptible

host

TIME

Incubation period

Death

Recovery

Exposure Onset

Latent Infectious

Infection

No infection

Clinical disease

e.g : Malaria– caused by protozoan parasites of the genus

Plasmodium– the stages of the parasite that are infective to

mosquitoes occur about 10 days after the development of symptoms

– latent period is around 10 days longer than the incubation period, so early treatment of symptoms could have an important effect on transmission

Natural history of disease

Susceptible

host

TIME

Incubation period

Death

Recovery

Exposure Onset

Latent

Infection

No infection

Clinical disease

Infectious

Latent Period of Chronic Disease

• Definition; "Interval between exposure to a disease-causing agent and the appearance of manifestations of the disease"

• cf. incubation period in infectious disease

Two conditions

1) brief exposure

2) prolonged or continuous exposure

Primary Prevention

• 'Preventing the occurrence of disease or injury by modifying risk factors.'

• 'Various aspects are considered to produce effective primary prevention program. Especially, advancing knowledge of disease causation must be required.‘

Primary Prevention• ** Guidelines for effective prevention programs(RB Wallace,

GD Everett,1986)– Programs must be based on scientific evidence.– Prevention programs should be supported by effective data

system.– Programs should be flexible.– Programs must be sensitive to ethical issues.– Programs should be targeted to the recipients most in need.– Programs should muster a variety of community resources.– Effective prevention requires legislative action and social policy

decisions.– Programs should be continuous.

Primary Prevention

• General health promotion– 'Proper nutrition, mental hygiene, adequate housing, and appropriate

balance between work and play, est and exercise, and useful and productive place in society, are among the best recognized factors ontributing to maintenance of optimum health.(Commission on Chronic illness, USA, 1957)‘

• Specific protection• Health Promotion

– 'Health promotion is any combination of educational, organizational, economic, and environmental supports for behavior and conditions of living conducive to health (LW Green, 1992).'

Criteria for the Development of Health Promotion and Education Programs

• A health promotion program should address one or more risk

factors which are carefully defined, measurable, modifiable,

and prevalent among the members of a chosen group, factors

which constitute a threat to the health status and the quality

of life of target group members.

• A health promotion program should reflect a consideration of

the special characteristics, needs, and preferences of its

target groups(s)

From APHA Technical Report

Criteria for the Development of Health Promotion and Education Programs

• health promotion programs should include interventions which will clearly

and effectively reduce a targeted risk factor and are appropriate for a

particular setting

• A health promotion program should identify and implement interventions

which make optimum use of available resources.

• From the outset, a health promotion program should be organized,

planned, and implemented in such a way that its operation and effects can

be evaluated.

MODES OF TRANSMISSION• DIRECT TRANSMISSION• DIRECT CONTACT• DROPLET INFECTION• CONTACT WITH SOIL• INOCULATION INTO SKINOR MUCOSA• TRANSPLACENTAL

• INDIRECT TRANSMISSION• VECHICLE BORNE• VECTOR BORNE• A) mechanical• B) biological• AIR-BORNE• FOMITE BORNE• UNCLEAN HANDS AND FINGERS

BIOLOGICAL TRANSMISSION

• Propagative• Cyclo-Propagative• Cyclo-developmental• Transovarial transmission• Trans-stadial transmission

SOURCE OF INFECTION

• It is defined as the person, animal, object or substance from which an infectious agent passes or is disseminated to the host

RESERVOIR

• It is defined as “any person, animal, arthropod, plant, soil, or substance “(or combination of these 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”

CARRIERS

A Carrier is defined as an infected person or animal that harbours a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection for others

CARRIERS

• TYPE

A) Incubatory

B) Convalescent

C) Healthy• DURATION

A)Temporary

B)Chronic

• PORTAL OF EXIT

A) Urinary

B) Intestinal

C) Respiratory

FEATURES OF CARRIER

1. Presence of specific microbes in the body

2. Absence of apparent symptoms and signs

3. Shedding of micro-organisms in the discharges or excretions

4. As a source of infection to others

INCUPATION PERIOD

THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION

FACTORS AFFECTING THE INCUPATION PERIOD

• DOSE OF INOCULUM• SITE OF MULTIFICATION• RATE OF MULTIFICATION• HOST DEFENCE MECHANISM

FACTORS TO DETERMINE THE INCUBATION PERIOD

• GENERATION TIME• INFECTIVE DOSE• PORTAL OF ENTRY• INDIVIDUAL SUCEPTIBILITY

IMPORTANCE OF INCUPATION PERIOD

• Tracing the source of infection and contact

• Period of surveillance• Immunization• Identification of point source or

propagated epidemics• Prognosis

MEDIAN INCUPATION PERIOD

• IT IS DEFINED AS THE TIME REQUIRED FOR 50% OF THE CASES TO OCCUR FOLLOWING EXPOSURE

LATENT PERIOD

IT HAS BEEN DEFINED AS THE PERIOD FROM DISEASE INITIATION TO DISEASE DETECTION

GENERATION TIME

IT IS DEFINED AS THE INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTIVITY OF THAT HOST

SERIAL INTERVAL

THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE

COMMUNICABLE PERIOD

It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person, from an infected animal to man , or from an infected person to an animal, including arthropods

SECONDARY ATTACK RATE

It is defined as the number of exposed persons developing the disease within the range of the incubation period, following exposure to the primary case

Number of exposed persons developing the SAR

= disease within the range of the incubation period 100

Total number of exposed /susceptible

HERD IMMUNITY

• IT IS THE LEVEL OF RESISTENCE OF A COMMUNITY OR GROUP OF PEOPLE TO A PARTICULAR DISEASE

BEHAVIOUR OF DISEASE IN THE COMMUNITY

1. EXOTIC

2. SPORADIC

3. ENDEMIC

4. EPIDEMIC

5. PANDEMIC

6. OUTBREAK

EPIDEMIC

It is the unusual occurrence in a community or region of cases of an illness, specific health-related behavior, or other health related events clearly in excess of normal expectancy (LAST,1995)

OUT BREAK

TWO OR MORE RELATED CASES IN INFECTIONS, SUGGESTING THE POSSIBILITY OF A COMMON SOURCE OR TRANSMISSION BETWEEN CASES

FACTORS IN DISEASE CAUSATION

1. Predisposing factors age, sex and previous illness

2. Enabling factors low income, poor nutrition, bad housing, inadequate medical care

3. Precipitating factors exposure to a specific disease agent

or noxious agent

4. Reinforcing factors repeated exposure, unduly hard work

THE EPIDEMIOLOGIC TRIANGLE

TRADITIONAL MODEL OF INFECTIOUS DISEASE CAUSATION

"triad" that play a role in disease process

Vector

Host Environment

Agent

As an element or substance, animate or inanimate,the presence (or absence) of it may initiate or perpetuate a disease process

AGENT

A person or other living animal, that affords subsistence or lodgment to an infectious agent under natural condition

Host factorsIntrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent

HOST

As the aggregate of all the external conditionsand influence affecting the life and development of an organism

Environmental factor Extrinsic factors which affect the agent and the opportunity for exposure

ENVIRONMENT

AGENT

a. Nutritional agent

carbohydrate, vitamin, fat, protein, mineral, water Example :

- diabetes mellitus, obesitas, hyperlipidemia, kwashiorkor - avitaminosis- cretinism, anemia- edema, dehydration

b. Chemical agent

polutan , drugs, Hg, Pb, Ag, arsenicum, pesticide (Chlorinated Hydrocarbon CCl4 : DDT, endrin, dieldrin and organo

hosphate, diacynon, malathion, butazinon), cosmetics, etc.

c. Physical agent collision, traffic accident, falling down, dust, climate (frost bite, heat stroke)

d. Infectious agent - Virus : dengue, morbili, varicella, hepatitis - Ricketsia : typhus exanthematicus, Rocky Mountain Spotted Fever, scrub typhus (rat-bite fever) - Bacteria : gram (+), gram (-) ; bacil, coccus, acid fast resistence, anaerob, etc. - Fungi : tinea capitis, tinea cruris, tinea pedis - Protozoa : plasmodium, amoeba - Metazoa : worm (ascaris , ancylostoma, etc.)

HOST

Intrinsic factors that play a role in disease process- age - sex- religion- customs- occupation- marital status- family background- genetic-hereditary- ethnic / race- physiologic / psychological status- habit / behavior- immune status- previous disease

1. Physical environment

geographic, geology, climate

2. Biological environment

people, flora, fauna, food population density

3. Socioeconomic

income, education, culture, urbanization, economic growth, poverty, fertility, etc.

ENVIRONMENT

NATURAL HISTORY AND SPECTRUM OF DISEASE


The progress of a disease process in an individual overtime in the absence of intervention

Exposure host disease

recovery

disability

death

The time interval between contact with an agent and the first clinical evidence of resulting disease

Depends on :• Portal of entry (defense mechanism)• The ability of multiplication (infectivity) • Number of agents • Level of antibody in the host

It varies individually

INCUBATION PERIOD

Type of incubation period in disease outbreak

A : skewed to the left the disease has a short incubation period

B : skewed to the right the disease has a longer incubation period

A B

time

number of cases

THE ABILITY TO REACT AGAINST AGENT INVASION IN THE BODY

Consist of :

• The external defense mechanism : physical and chemical reaction

• The internal defense mechanism : cellular and humoral immunity

DEFENCE MECHANISM

Respiratory tract sense of smell, cough and sneeze reflex, mucous membrane, hair of the nose, ciliated epithelium. Small particles < 5 can enter directly into the alveoli.

Digestive tract sense of taste, vomit reflex, gastric acid fluid, peristaltic of intestine and diarrhea

Skin structure of the skin, sebaceous glands, apocrine and accrine sweat glands, hair

Eye blink reflex, eye brow, eye lash, tears

EXTERNAL BARRIER

If the external barrier can not eliminate the agent

internal defense mechanism will continue the defence mechanism process by :

- Inflammation

- Isolation by fibrocyte

- Macrophage phagocytosis

- Antibody reaction

Immunization a way to increase the internal

defence mechanism

The natural history and spectrum of disease challenges to the clinician

and to the public health worker

To the clinician

Because of cases diagnosed by clinicians in the community often represent only the “tip of the iceberg”, it is important to do the “case finding” and report it to the public health worker

To the public health worker

While searching the rest of the cases, they should prevent disease transmission and outbreak

ICEBERG PHENOMENE ICEBERG PHENOMENE

CLINIC

CLINICAL HORIZON

SUB CLINIC CURE

The proportion of sub clinical patients are greater in number than the patients with complete symptoms

This portion should be early detected, because it has the capability of transmitting the disease causing outbreak

CELL RESPONSE

Lysis of cell

HOST RESPONSE

Death of organism

Inclusion body formationor

cell transformationor

cell dysfunction

Classical and severe disease

Moderate severity mild illness

Viral multiplication

without visible

change or

incomplete viral

maturation

Exposure without

attachment and/or

cell entry

Infection without

clinical illness

(asymptomatic infection)

Exposure without

infection

Dis

cern

able

effe

ctBe

low

vis

ual

chan

geClinical disease

Subclinical disease

CHAIN OF INFECTION

1. Natural characteristics of the agent

The morphology, physiology, reproduction, motility, metabolism, need of oxygen , temperature, production of toxin, antigen, living cycle, reaction against physical and chemical substance

2. Characteristic of the agent related to infection in human

a. infectivity

b. pathogenicity

c. virulence

d. antigenicity

e. tropism

AGENT CHARACTERISTIC

3. Reservoir of agent

4. Portal of entry and portal of exit

5. The incubation period

6. The spread of the disease

7. Natural cycle of infection

INFECTIVITY

The ability of agent to attack, adapt, live and multiplicate in the host

PATHOGENICITY

The ability of agent to produce a local or general reaction in the host

VIRULENCE

The ability to elicit a severe clinical manifestation

ANTIGENICITY

The agent’s ability to stimulate host production of antibody such as agglutinin, opsonin, precipitin, antitoxin, lysine, complement fixating substance,etc.

Disease with high antigenicity can be prevented by immunization

Example :

• Typhoid fever, morbili : highly antigenic

• Tuberculosis : doubtful

• Influenza virus has lots of strain :

rather difficult to develop an effective vaccine

Agent with high infectivity and pathogenicity but low antigenicity will cause a relatively high disease prevalence in the community

Agent with high infectivity but low pathogenicity usually produce a mild or sub clinical symptom and carrier

TROPISM

The agent preference to attack and stay in special location in the host• Cholera : digestive tract• Staphylococcus : mostly in the skin• Herpes zoster : nerve system• Poliomyelitis : anterior-horn cells of spinal cord

HERD IMMUNITY

The immunity of a group of people / community.

The resistance of a group to invasion and spreading of an infectious agent

based on the resistance to infection of a high proportion of individual members of the

group.

The herd immunity reduces the susceptibility to infection or can resist a communicable

disease epidemic.

The higher herd immunity the higher the power to defence of an epidemic

occurrence.

The high incidence of communicable disease can be due to :

the high proportion of the susceptible individual

or the low portion of herd

immunity in the population

The practical aspect of the concept of herd immunity : the necessity of

immunization program for the whole population to prevent the occurrence of an

epidemic

Habitat in which an infectious agent normally lives, grows and multiplies

1. HUMAN RESERVOIR

2. ANIMAL RESERVOIR

3. ENVIRONMENTAL RESERVOIR

RESERVOIR

1. Human reservoir

- Persons with symptomatic illness

- Carrier

Carrier : a person without apparent disease who is nonetheless capable of transmitting the agent to others

a. Asymptomatic carrier (never show symptoms during the time they are infected)

b. Incubatory / convalescent carrier (who are capable of transmission before or after they are clinically ill)

c. Chronic carrier (who continues to harbor an agent)

2. Animal reservoirInfectious disease that are transmissible under normal conditions from animals to human are called zoonoses

• Dog, cat, ape : rabies• Rat : rat bite fever, plaque, leptospirosis• Cattle : sheep, goat, camel, cow, pig (anthrax, brucellosis, bovine tuberculosis, tularemia,

ring worm)• Arthropode : flies, cockroach, mosquito

3. Environmental reservoir (soil)

•Clostridia (tetanus, botulism, welchii)

•Fungi

•Bacteria

(dust particle : mycobacterium tuberculosis)

•Parasite (helminthiasis)

The path by which an agent enters of leaves the source host.

Usually corresponds to the site at which the agent is localized.

It is necessary to understand about it because it related to how the disease being transmitted in other way we can assume how the prevention of the disease.

PORTAL OF ENTRY AND PORTAL OF EXIT

Portal of entry- digestive tract- respiratory tract- skin- genital- eye - blood vessel system

The portal exit seem to be the same with the portal entry, sometimes some disease have other way of exit beside the former way.

Hepatitis infectiosa, typhus abdominalis :

beside come out by fecal also can be detected in urine and blood.

4 transmission ways :

1. Contact transmission

a. Direct transmission :

by mucous contact

e.g. genital-genital, oral-genital, oral-oral

b. Indirect :

hand-mouth, droplet transmission

TRANSMISSION

2. Vehicle transmission

- Transmission by common vehicle :

food, fluid, milk, blood, serum, vaccine

- The agent can be transmitted by ingestion, injection or inoculation

3. Vector transmission

The arthropods have a role in this transmission

4. Air borne - droplet nuclei - dust

Transmission of Dengue Virusby Aedes aegypti

Viremia Viremia

Extrinsic incubation

period

DAYS0 5 8 12 16 20 24 28

Human #1 Human #2Illness

Mosquito feeds /acquires virus

Mosquito refeeds /transmits virus

Intrinsicincubation

period

Illness

Replication and transmissionof Dengue virus (part 1)

1. Virus transmitted to human in mosquito saliva

2. Virus replicates in target organs

3. Virus infects white blood cells and lymphatic tissues

4. Virus released and circulates in blood

3

4

1

2

Replication and transmissionof Dengue virus (part 2)

5. Second mosquito ingests virus with blood

6. Virus replicates in mosquito midgut and other organs, infects salivary glands

7. Virus replicates in salivary glands

6

7

5

Theoretically, the spreading of the disease can be stopped by cutting off every step of the disease phase.

The principle of communicable disease control is to cut off the chain of transmission of the disease.

Example :1. To cut the connection between the reservoir and

the host (contact person) by :• individual hygiene• environmental sanitation

2. To increase the defense mechanism by :• immunization• nutrition

3. In case the colonization has been occurred :• early diagnosis & prompt treatment• screening : malaria, STD, HIV-AIDS

By knowing how an agent exits and enters a host, and what its modes of transmission are, we can determine appropriate control measures, including prevention methods

Patients may be treated and/or isolated with appropriate “precautions”

IMPLICATION

FOR PUBLIC HEALTH

FOR CLINICAL/HOSPITAL SETTING

NATURAL HISTORY OF ANY DISEASE

PREPATHOGENIC PATHOGENIC

Agent Host

Environment

CLINICAL

Sub Clinic Convalescence Cured + Sequel

Clinical Horizon

1 2 3

PRIMARY PREVENTION I

SECONDARYPREVENTION II

TERTIARY PREVENTION III

interaction

D E A T H

I. PRIMARY PREVENTION “Health promotion and specific protection”

A. Health Promotion

1. Health education

2. Nutrition

3. Development

4. Housing

5. Marriage counseling

6. Genetic

7. Periodic physical examination

STAGE OF PREVENTION

B. Specific protection1. Immunization

2. Personal hygiene

3. Environmental sanitation

4. Occupational hazard

5. Protection to accident

6. Specific nutrition

7. Protection to carcinogen

8. Avoidance of allergic material

II. SECONDARY PREVENTION “Early diagnosis and prompt treatment”

1. Case finding

2. Screening survey

3. Selective examination

a. Cure and prevent

b. Preventing the spread

c. Preventing complication and sequel

d. Shorten of disability


Stage ofsusceptibility

Stage of subclinical disease

Stage of clinical disease

Stage of recovery, disability or death

PRIMARY PREVENTION SECONDARY

PREVENTION TERTIARY PREVENTION

Exposure

Pathologicchanges

Onset of symptoms

Usual time of diagnosis

The natural history of disease

STAGE 1: Susceptibility

DESCRIPTION: Risk factors which assist the development of

disease exist, but disease has not developed

EXAMPLE: Smoking

The natural history of disease (cont’d)

STAGE 2: Presymptomatic disease

DESCRIPTION: Changes have occurred to lead toward illness but disease is not yet

clinically detectable

EXAMPLE: Alveoli deteriorate


STAGE 3: Clinical Disease

DESCRIPTION: Detectable signs and/or symptoms of disease exist

EXAMPLE: Emphysema detected by pulmonary function test


STAGE 4: Disability

DESCRIPTION: Disease has progressed to the point of causing a

residual effect

EXAMPLE: Person has difficulty breathing

LEVELS OF PREVENTION

LEVEL: Primary

DESCRIPTION: Promote general health

and avoid risk factors for

disease --- Utilize protective measures to prevent

susceptibility and presymptomatic disease

EXAMPLE: Stop smoking or choose not to start; avoid areas

where people are smoking

LEVELS OF PREVENTION (cont’d)

LEVEL: Secondary

DESCRIPTION: Early detection and timely treatment

EXAMPLE: Routine pulmonary function tests for those at risk; medicine to help

patients breath more easily; smoking cessation

programs if patient smokes

LEVELS OF PREVENTION (cont’d)

LEVEL: Tertiary

DESCRIPTION: Rehabilitation and prevention of further

disease or disability

EXAMPLE: Oxygen therapy; facilitating ambulation with technical devices

PREVENTION APPROACHES

Population-Based Approach:• Preventive measure widely applied to

an entire population (public health approach)

• Strive for small absolute change among many persons

• Must be relatively inexpensive and non-invasive

PREVENTION APPROACHES

High-Risk Approach:

• Target group of individual at high risk

• Strive for strong risk factor control

• Often times requires clinical action to identify the high risk group and to motivate risk factor control.

LEVELS OF PREVENTION (Review)

PRIMARY PREVENTIONPrevention of disease by

controlling risk factors (e.g.,

non-smoking promotion)

Reduction in consequences of disease

by early diagnosis and treatment

(e.g., cervical cancer screening)

LEVELS OF PREVENTION (Review)

SECONDARY PREVENTION

concept of disease

Technology