DISEASE PREVENTION
AND CONTROL
Direslgne Misker
1
Learning Objectives
At the end of the class, You are expected to
 Develop basic concepts of measurements of
diseases
 Identify the principles of disease prevention and
control
 Differentiate the levels of disease prevention
2
MEASUREMENT OF THE OCCURRENCE OF
DISEASES
Why Measurement?
 Measurement is the basis for evidence based
practice:
The
two
fundamental
principles
of
epidemiology that a given health event does not
occur by chance and that its distribution is not
uniform in any population necessitate for
measurement
in
order
for
properly
understanding and hence making necessary
decisions;
3
Why Measurement?
Understanding
of
the
occurrence,
consequences, the need for/the burden on/
services
and
the
effect
of
targeted
interventions as related to a given health event
cannot
be
substantiated
without
having
/making the proper measures related with
each of the above;
 Making Comparisons
4
MEASUREMENT OF THE OCCURRENCE OF
DISEASES
What Can be Measured?
 Occurrences of Diseases :
Risk factors
Cases
Spread
 Consequences of Diseases:
Disabilities,
Deaths
 Need for/ burden on/ services
Hospitalization rates
 Effect of targeted interventions
Cases/ disabilities/deaths averted
Quality of care
5
MEASUREMENT OF THE OCCURRENCE OF DISEASES…
 Index Case
 Person that comes to the attention of public health
authorities
 Primary Case
 Person who acquires the disease from an exposure
 Attack rate
 Secondary Case
 Person who acquires the disease from an exposure to the
primary case
 Secondary attack rate –This is a measure of the degree of
spread
6
MEASUREMENT OF THE OCCURRENCE OF DISEASES…
Calculation of Attack Rate for Food X
Ate the food (exposed)
Did not eat the food (not exposed)
Ill
Well
Total
Attack
Rate
Ill
Well
Total
Attack
Rate
10
3
13
76%
7
4
11
64%
Number of Ill
Attack Rate 
X 100
# of Ill  # of Well
Attack Rate among who ATE 
10
X 100  76%
10  3
Attack Rate among who did NOT EAT 
Re lative Risk (RR)
7
X 100  64%
74
Attack Rate among who ATE
76

 1.2
Attack Rate among who did NOT ATE
64
7
MEASUREMENT OF THE OCCURRENCE OF DISEASES…
Secondary Attack Rate
Population
Age in
Years
Cases
Total
No. susceptible
before primary cases
occurred
Primary
Secondary
2-4
300
250
100
5-9
450
420
204
10-14
152
84
25
50
87
15
Secondary Attack Rate 
Secondary Attack Rate ( 2  4Years) 
Total Number of Cases  Number of Initial Cases
X 100%
Number of Susceptibles in the group  Number of Initial Cases
Total Number of Cases  Number of Initial Cases
150  100
X 100% 
X 100%  33%
Number of Susceptibles in the group  Number of Initial Cases
250  100
8
MEASUREMENT OF THE OCCURRENCE OF DISEASES…
Secondary Attack Rate
Used to estimate the spread of disease in a family,
household, or other group environment.
Measures the infectivity of the agent and the effects
of prophylactic agents (e.g. vaccine)
9
MEASUREMENT OF THE OCCURRENCE OF
DISEASES
Measurements Related with the Occurrence of Chronic Diseases
 Proportion of people with a specific Risk Factor :
Example: Proportion of smokers
 Frequency of Occurrence:
Incidence, Prevalence
 Consequences of Diseases:
Disabilities,
Deaths
 Need for/ burden on/ services
Hospitalization rates
 Effect of targeted interventions
DALY, HALE, Survival time
10
Health Adjusted Life Expectancy
(HALE)
 Summarizes the expected number of years
to be lived in good health
 To calculate HALE, the years of ill health
are weighted according to severity and
subtracted from the overall life expectancy
11
Disability Adjusted Life Year (DALY)
 Is a unit for measuring the amount of health lost
because of particular disease or injury
 DALY is a measure of premature deaths and
losses due to illness and disabilities in a
population.
12
13
Calculation of HALE and DALY
 In a given country the life expectancy is 80
years. A person develops deafness at 50 years
which is counted as 40% as “bad” as a year of
life lost due to premature death. If this person
died at 70 years
1. What is Health Adjusted Life Expectancy
(HALE?
2. What is Disability Adjusted life Year (DALY)?
14
Solution
0
Birth
50
Disability
70
80
Life
Expectancy
Death
HALE=years lived with full health +years lived with disability
=50 Years+20years*0.6=62 years
DALE= Years lost due to Disability + Years of Life Lost
= (20*0.4) + 10=18 years
15
Class work
 In a given country the life expectancy is 66
years. A person develops blindness at 30 years
which is counted as 70% as “bad” as a year of
life lost due to premature death. If this person
died at 60 years
1. What is Health Adjusted Life Expectancy
(HALE?
2. What is Disability Adjusted life Year (DALY)?
16
GENERAL PRINCIPLES IN THE PREVENTION AND
CONTROL OF COMMUNICABLE DISEASES
How is it possible to have General Principles for the Prevention and
control of Communicable Diseases?
 Communicable diseases as a specific class of diseases can
more often be characterized by common features than non communicable diseases (NCDs), irrespective of the place and
time of their occurrence and the people they affect.
 Despite their diversity, communicable diseases share common
considerations in the general principle or approach in terms
their control and prevention.
 Communicable diseases, however, differ when the applicability
and the degree of effectiveness of each of the specific control
and prevention measure is taken into account.
17
GENERAL PRINCIPLES IN THE PREVENTION AND CONTROL OF
COMMUNICABLE DISEASES
How is it possible to have General Principles for the Prevention and
control of Communicable Diseases?...
 The general principles in the control and prevention of
communicable diseases are based upon three factors
involved in the chain of disease transmission
The Reservoir
The Mode of Transmission, and
The Susceptible Host
18
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir: HUMAN
 The specific types of control measures aiming on the human
being depends on its specific reservoir role as a CASE or a
CARRIER of the particular disease
 Human being as a Case
 Case –detection and treatment: the process of identifying and
treating people with the disease so as to render them
unimportant as a source of infection, by reducing the
communicability of the disease.
Active case detection: active search for cases of a given
disease ensures the early identification of people with
19 the
disease before the disease puts an irreversible damage
GENERAL PRINCIPLES IN THE PREVENTION &
CONTROL OF CDs
Measures directed at the Reservoir: HUMAN
 Screening: detecting cases at earlier stages of disease
development on apparently well people.
Screening as an initial examination is not usually
diagnostic and requires appropriate investigative
follow -up and treatment.
It is a vital tool for control & prevention of diseases
that benefit from active case -detection and
treatment.
 Isolation: the separation, for the period of
communicability of the disease, of infected persons or
animals from others so as to prevent or limit the
transmission of the infectious agent from those
infected to those who are susceptible to infection or
who may spread the agent to others.
Isolation is not indicated for every CD
20
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir: HUMAN
 Isolation is indicated for infectious diseases having:
 High morbidity and High mortality
 High infectivity in which maximal infectivity does not precede
overt illness
 Non –significant extra –human reservoir:
 Easily recognizable infectious cases;
 Non –significant carriers
 The use of isolation is often variable from country to country,
partly depending up on the level of development of the health care
services
21
Category specific Isolation (CDC):
Strict isolation- Diseases spread by both air and contact
Contact isolation- Diseases spread by touching
Respiratory isolation- diseases spread by exhaled
Enteric Precautions- direct or indirect oral contact with
faeces and articles
Drainage /Secretion Precautions- Direct contact with oral
secretions, fecal excretions, wound secretions
22
Standard precautions for Isolation
Hand Hygiene
Use of PPE(Gloves, Masks, Eye wear)
Respiratory hygiene/Cough Etiquette
Clean and disinfect environmental surfaces
Safe injection practices including Sharps safety
23
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir: HUMAN
 Two basic requirements for care of all potential
infectious cases are:
 Hands must be washed after contact with the
patient or potentially contaminated articles before
taking care of another patient; and
 Articles contaminated with infectious material
should be appropriately discarded or bagged and
labelled before being sent for decontamination and
reprocessing
24
 Quarantine:
the
limitation
of
the
movement
of
apparently well people who are considered to have been
exposed to a source of infection for the maximum
duration of the incubation period
Absolute
/Complete/
Quarantine
–
implies
absolute prohibition of entrance to or exit from
quarantined premises
Modified Quarantine- Allows, under certain
restrictions, the passing in and out of persons in
the family
25
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir:
HUMAN
 Personal Surveillance: the practice of close medical
or other supervision of contacts to permit prompt
recognition
of
infection
or
illness
but
without
restricting their movements;
 Segregation: the separation of some part of a group
of persons or domestic animals from the others for
special consideration, control or observation; removal
of susceptible children to homes of immune persons;
or establishment of a sanitary boundary to protect
uninfected from infected portions of a population.
26
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir: Animals
 When animals are the reservoirs of infection, decision
on the type of measures to be taken should consider:
 The relation of the animal with human beings
 The usefulness of the animal
 The feasibility of protecting susceptible animals
27
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed at the Reservoir: Animals
28
GENERAL PRINCIPLES IN THE
PREVENTION & CONTROL OF CDs
Measures directed at the Reservoir: Non
living things
 Limit the exposure of people to the affected or
suspected area. e.g., soil, water, etc
29
GENERAL PRINCIPLES IN THE PREVENTION & CONTROL
OF CDs
Measures directed On the MODE OF TRANSMISSION
 These measures are meant to break or interrupt
the chain of transmission from the reservoir to the
susceptible host
 Vector control
 Improving environmental sanitation and personal hygiene
 Disinfection and sterilization
 Health Education
30
GENERAL PRINCIPLES IN THE PREVENTION &
CONTROL OF CDs
Measures Directed On The Protection Of The Susceptible
Host
Increasing the host resistance
Decreasing or minimizing exposure of the
host
31
Levels of disease prevention
Successful prevention depends on
Knowledge of causation
Dynamics of transmission
Identification of risk factors and risk groups
Availability of prophylactic or early detection and
treatment measures
Facility for these treatment procedures
Evaluation and development of these procedures
32
Levels of disease prevention
1. Primordial prevention
2. Primary prevention
3. Secondary prevention
4. Tertiary prevention
33
Primordial prevention
 It is the prevention of the emergence or
development of risk factors in countries or
population groups in which they have not yet
appeared
 E.g. smoking, eating patterns, physical exercise
 The main intervention is through individual and
mass education
34
Primary prevention
 An action taken prior to the onset of disease,
which removes the possibility that the disease
will ever occur.
 It signifies intervention in the pre-pathogenesis
phase of a disease
 Accomplished by measures of “Health
promotion” and “specific protection”
35
Primary prevention
Achieved by
Health promotion
Specific protection
Health education
Environmental modifications
Nutritional interventions
Life style and behavioral changes
Immunization and prophylaxis
chemoprophylaxis
Use of specific nutrients or supplementations
Protection against occupational hazards
Safety of drugs and foods
Control of environmental hazards,
e.g. air pollution
36
Interventions for primary prevention
 Population (mass) strategy
High -risk strategy
37
Secondary prevention
 An action which halts the progress of a disease at its
incipient stage and prevents complications
 Attempts to arrest the disease process, restore health by
seeking out unrecognized disease and treating it before
irreversible pathological changes take place, and reverse
communicability of infectious diseases.
 Interventions are: early diagnosis (e.g. screening tests,
and case finding programs….) and adequate treatment.
38
Tertiary prevention
 Used when the disease process has advanced
beyond its early stages
 All the measures available to reduce or limit
impairments and disabilities, and to promote the
patients’ adjustment to irremediable conditions
 Interventions: Disability limitation and
rehabilitation
39
Concept of control
 The term disease control describes ongoing
operations aimed at reducing:
The incidence of disease
The duration of disease and consequently the risk of
transmission
The effects of infection, including both the physical
and psychosocial complications
The financial burden to the community.
40
Public health approach to disease control
41
STAGES / LEVELS / OF DISEASE Control
Control
 Is reduction of disease incidence, prevalence, or
mortality to a locally acceptable level as a result of
deliberated efforts
 Marked reduction in indigenous transmission to the
point where disease incidence no longer presents a
major public health problem
 continued intervention measures are required to
maintain the reduction
42
Elimination
 Reduction of case transmission to a predetermined
very low level
 It is either reduction of an infectious disease's
prevalence in a regional population to zero or
 The reduction of the global prevalence to a negligible
amount
 An important precursor of eradication
 Continued intervention measures are required
43
Eradication
 Permanent reduction to zero of the worldwide incidence
of infection caused by specific agent as a result of
deliberate efforts
 This is the complete worldwide cessation of natural
transmission.
 All control measures can be dropped after certification of
eradication.
 e.g. Small pox
44
45
Factors that favour eradication of a
communicable disease:
 Characteristics of the infectious agent, such as its
immunogenicity in humans, the absence extra –
human reservoir
 Presence of efficacious and effective, affordable,
acceptable, and safe vaccines);
 Political commitment at national and international
levels
46
Factors that favour eradication
of a communicable disease...
 Good organization and coordination of health
services and logistic support, and
 Social mobilization for the promotion of active
community participation / involvement
 Presence of sensitive and specific tools for
diagnosis and surveillance
47
Reasons that smallpox could be targeted for
eradication when many other infectious
diseases could not include:
 Humans are the only known reservoir for the disease,
therefore, if transmission from human to human could be
stopped, the disease could be eliminated as there is no animal
reservoir that would contribute to continued circulation.
 Practical diagnostic tools were available to assist in the
diagnosis and confirmation of smallpox cases
 A vaccine was available that could effectively protect
individuals from disease for several years (or longer if
repeated), therefore, interrupting transmission was possible
48
49