CHAPTER TWO

EPIDEMIOLOGY IN COMMUNITY HEALTH

Unit of learning code: HE/CU//CH/CC/02/5/A

Related Unit of Competency in Occupational Standard: Apply Epidemiology in Community

Health

Introduction to the unit of learning

This unit specifies the competencies required to apply epidemiology in community health. It
involves conducting disease surveillance, carrying out population screening and monitoring
disease occurrence. It also includes utilizing epidemiology data in community health.

Summary of Learning Outcomes

1 Conduct disease surveillance
2 Carry out population screening
3 Monitor disease occurrence
4 Utilize epidemiology data

Learning Outcome 1: Conduct disease surveillance

Introduction to the learning outcome

In this unit, you will learn how to conduct disease surveillance. This will involve planning
disease surveillance, identifying methods of data collection, carrying out disease surveillance,
carrying out population screening and preparing disease surveillance report

Performance Standard
Disease surveillance is planned as per disease surveillance procedures
Methods of data collection are identified according to health protocols
Disease surveillance is carried out as per health protocols
Population screening is carried out in accordance with screening plan
Disease surveillance report is prepared and disseminated according to disease surveillance
requirements
Definitions of terms
Surveillance: the ongoing systematic collection, analysis and interpretation of health data
essential to the planning, implementation and evaluation of public health.
Determinants: factors which determine whether or not a person will get a disease
Disease: a type of internal state which is either an impairment of normal functional ability–that
is, a reduction of one or more functional abilities below typical efficiency–or a limitation on
functional ability caused by environmental agents”
Disease surveillance: is an information-based activity involving the collection, analysis and
interpretation of large volumes of data originating from a variety of sources.
Distribution: refers to the geographical distribution of diseases, the distribution in time, and
distribution by type of persons affected.
Endemic-The habitual presence of a disease within a given geographical area. It may also refer
to the usual occurrence of a given disease within such an area
Epidemic-the occurrence of a disease in a community of a group of illnesses of similar nature
clearly in excess or beyond normal expectancy
Epidemiology: is the study of the distribution and determinants of health-related states or events
in specified populations, and the application of this study to the control of health problems.
Frequency: the number of times an event occurs
Incidence: number of new cases of a disease within a specified time period.
Incubation period: interval between exposure to an infectious agent and the onset of the disease
it causes.
Natural history: sequence of developments from earliest pathological change to resolution of
disease or death
Pandemic-this is a disease occurring worldwide
Pattern: refers to the occurrence of health-related events by time, place, and personal
characteristics.
Prevalence: the number of cases of a condition (old and new) in a given population at a point in
time.

Public Health Surveillance

Public health surveillance is the ongoing, systematic collection, analysis, interpretation, and
dissemination of health data to help guide public health decision making and action.
Concepts of disease surveillance
Epidemiology
Disease surveillance
Frequency measures
Mortality
Epidemic
Endemic
Epidemiology
What is epidemiology?
Epidemiology is the study of the determinants, distribution, and frequency of disease (who gets
the disease and why)
epidemiologists study sick people
epidemiologists study healthy people
to determine the crucial difference between those who get the disease and those who are spared
epidemiologists study exposed people
epidemiologists study non-exposed people
to determine the crucial effect of the exposure
Epidemiology is used to;
determine, describe, and report on the natural course of disease, disability, injury, and death
aid in the planning and development of health services and programs
provide administrative and planning data
study the cause (or etiology) of disease(s), or conditions, disorders, disabilities, etc.
determine the primary agent responsible or ascertain causative factors
determine the characteristics of the agent or causative factors
determine the mode of transmission
determine contributing factors
identify and determine geographic patterns
Types of epidemiology
There are two broad types of epidemiology;
descriptive epidemiology: examining the distribution of disease in a population, and observing
the basic features of its distribution
analytic epidemiology: investigating a hypothesis about the cause of disease by studying how
exposures relate to disease
Analytical epidemiology studies require information to know where to look, what to control for
and to develop viable hypotheses. Descriptive epidemiology looks at three essential
characteristics of disease which include person, place and time

Relevance of Epidemiology to community health

The practice of health care is dependent on population data available from epidemiology.
Selection of appropriate therapy is also population based. The data available about diseases in a
community can be very helpful in suggesting a diagnosis even if they are not conclusive.
Although this data may not make the diagnosis they give the health care a clue of what to
suspect.

Epidemiological triangle (triad of disease)

Figure 1: Epidemiologic triad of disease

A common model used in public health illustrates the relationships among an agent, a host and
the environment. It applies to biological, chemical and physical agents. For a disease or injury to
occur, the basic elements of disease or injury causation and an adequate chain of transmission
(i.e. environmental pathway) must be present.
Disease occurs when an outside agent capable of causing the disease or injury meets a host that
is vulnerable to the agent in an environment that allows the agent and host to interact. These
basic concepts help guide the selection of health strategies to prevent health problems.
One of the key jobs for the health professional is to intervene at any point in order to reduce the
hazard to health.

Many of the underlying principals governing the transmission of disease are most clearly
demonstrated using communicable disease as a model.
Diseases do not arise in a vacuum but as a result of interaction of infectious of other type of
agents and the environment that promote exposure in development of disease. Human
susceptibility is determined by a variety of factors including the genetic background, nutritional
and immunological characteristics.

Disease surveillance
Surveillance is undertaken to inform disease prevention and control measures
Most data about morbidity and mortality comes from programme of systematic diseases
surveillance. Surveillance is most frequently conducted for infectious diseases but in recent years
it has become important to monitor disease such as cancer and other noncommunicable diseases.
Surveillance is also used to monitor for completeness of vaccination coverage and protection of a
population from drug resistant organisms. The Centre for Disease Control defined surveillance
as the ongoing systematic collection, analysis and interpretation of health data essential to
the planning, implementation and evaluation of public health. It also involves timely
dissemination of this data to those who need to know. The data helps those involved in decision
making with guidance in implementing the best strategies for programme. There are two types of
surveillance;
Active
Passive
Passive surveillance
It denotes surveillance in which either available reportable diseases are used or reporting
mandate or requested by district health officer.
Active surveillance
It denotes a system where by project staff make periodic visists to the health. They identify new
cases of diseases from certain disease or deaths from certain diseases. They are involved in
interviewing physicians and receiving medical records. Surveillance is of great value in
identifying cases that could have otherwise gone undetected. It also useful in assessment of
changes in levels of environmental risk factors for a disease.

The information collected during disease surveillance is used to:

serve as an early warning system, identify public health emergencies
Identify high risk populations or areas to target interventions
Evaluate the effectiveness of control and preventative health measures
Monitor changes in infectious agents e.g. trends in development of antimicrobial resistance
Support health planning and the allocation of appropriate resources within the healthcare system.
Provide a valuable archive of disease activity for future reference.
guide public health policy and strategies
document impact of an intervention or progress towards specified public health targets/goals
understand/monitor the epidemiology of a condition to set priorities and guide public health
policy and strategies
Functions of surveillance system
detection and notification of health events
collection and consolidation of pertinent data
investigation and confirmation (epidemiological, clinical and/or laboratory) of cases or outbreaks
routine analysis and creation of reports
feedback of information to those providing the data
feed-forward (i.e. the forwarding of data to more central levels)
reporting data to the next administrative level

Factors that cause human diseases

These may include biological, physical and chemical factors as well. Stress may also cause
disease.
Factors associated with increased physical human disease
Age
Sex/Gender
Race
Religion
Custom/Tradition
Occupation
Genetic Profile
Marital Status
Immune Status

Factors that may be associated with increased risk of human diseases

Host characteristics
Types of agents eg bacteria, protozoa,viruses, fungi,helminthes
Chemical agents i.e poison, alcohol and smoke
Physical agent
These are: trauma, radiation and fire
Nutritional agent
Lack of some of the important food and minerals lead to the risk of developing certain diseases
e.g.
lack of iron –anaemia
lack of vitamin C (scurvy)
Lack of carbohydrate-malnutrition
Lack of protein-Protein Energy Malnutrition
Lack of vitamin B (beriberi)
Excessive amount of some of the micronutrients may also lead to development of a disease ie
haematochromatosis due to iron overload
Environmental factors
temperature: temperature may be conducive for thriving of certain biological agents of disease
humidity: certain humid levels can be enable transmission of certain biologic agents i.e the
bacteria causing meningitis
altitude: it affects some of the physiological processes of the body
crowding: these translate to poor hygiene practices that lead to transmission of infectious agent
pollution: generation of harmful fumes from industries can lead to development of respiratory
diseases

Natural history of disease

It’s a process through which a disease course from its beginning till the affected person either
recovers, becomes disabled or dies. Most people make full recovery from a disease but some
suffer damage to their body and may be left with permanent disability. If a disease is very severe
it may lead to death. The process can be summarized as follows;
Induction – time to disease initiation
Incubation – time to symptoms (infectious disease)
Latency – time to detection (for non- infectious disease) or to infectiousness
Disease patterns
Normally people should be well physically, mentally, socially and spiritually. But this is not
always the case. In any population there will be people who have a disease and thus are not
healthy.
Diseases occur differently in different population. The patterns of disease show how oftenly it
occurs in population and its distribution in terms of person, places and time. The patterns of
disease also shows relative importance in causing sickness and death (mortality-sickness and
morbidity-death). Some diseases are preventable by acquiring different measures. Some are not
preventable and only curative treatment can be used. It shortens the period of illness or prevents
it from getting worse.
Practical control measures should be given high priority for preventive action. These applies to
important and widely distributed diseases.
Disease distribution
A look at report from health facilities shows diseases for which people seek health care and how
often these diseases occur. It will also show the people who suffer from the disease, where they
come from and the time of the year that the diseases occur most. Some diseases occur more
frequently in certain group and in particular groups of people. Some occurs in certain places at
particular time of the year thus the frequency of a disease as well as distribution can be described
in terms of how often it occurs in different people in different places and at different time.
Those diseases which are always present in a community e.g. TB are called endemic. Those
which occur unexpectedly with large number of new cases e.g .cholera and meningitis are said to
be epidemic. New cases of endemic diseases occur regularly but in epidemics the the number
rises sharply. The number of new cases of disease occurring in a given population over a
specified period of time is called incidence.
It shows the rate of development of disease in the community. It’s the best measure of what
changes are occurring regarding the pattern of disease as well as the distribution. The total
number of cases (new and existing cases) of disease present in a given population at a particular
point is called prevalence.
Prevalence: the proportion of a defined population with the disease/event of interest at a
specified time period.
Prevalence is snap shot of disease frequency at a point in time. Point prevalence is the most
common measure of prevalence. Prevalence is often by cross-section surveys. An incident case
becomes a prevalent case and remains a prevalent case until recovery or death.
Where a population is in a ‘steady state’, prevalence depends on incidence and duration of
disease.
Prevalence is increased by:
longer duration of disease
prolongation of life without cure
increase in new cases
in-migration of cases
out migration of healthy people
improved diagnosis
Prevalence is decreased by:
short duration of disease
high case-fatality rate from disease
decrease in new cases
in-migration of healthy people
out-migration of cases
improved cure rate
Prevalence shows the magnitude or burden of a disease in medical services has to deal with and
in a useful measure of planning and administration of health care services. It is also useful in
measuring chronic conditions that change slowly like leprosy. Thus incidence shows the number
of new cases and records intense shortlived diseases while prevalence records chronic diseases.

Planning disease surveillance system

Identification of data collection methods

Morbidity and mortality reports are common sources of surveillance data for local and state
health departments. These reports generally are submitted by health-care providers, infection
control practitioners, or laboratories that are required to notify the health department of any
patient with a reportable disease such as pertussis, meningococcal meningitis, or AIDS. Other
sources of health-related data that are used for surveillance include reports from investigations of
individual cases and disease clusters, public health program data such as immunization coverage
in a community, disease registries, and health surveys.
Carrying out disease surveillance
Standard case definition is used to decide if a person has a particular disease, or if the case can be
considered for reporting and investigation. When counties and health care facilities use the same
case definition, the country’s public health surveillance system ensures efficient tracking of
particular diseases or conditions. The Health staffs who analyse data will be able to know the
trends of diseases under surveillance. The standard case identification is used as follows;
Patient comes to consultation room
Ask about symptoms and duration
Conduct physical examination and record findings on OPD card
Make diagnosis based on signs and symptoms
Match signs and symptoms with that of case definition
Record information about suspected cases in clinic register and patient card
Report case-based information for immediately notifiable disease using the IDSR reporting tools
Disease surveillance systems in Kenya
CDC Kenya supports the development and implementation of population and facility-based
disease surveillance systems that are used for data collection, analysis, and reporting. These
surveillance systems assess disease burden in communities, identify outbreaks, guide public
health action and evaluate the impact of health interventions.
Community-based surveillance
Community-based Surveillance (CBS) is an active process of community participation in
detecting, reporting, responding to and monitoring health events in the community.
The scope of CBS is limited to systematic on-going collection of data on events and diseases
using simplified case definitions and forms and reporting to health facilities for verification,
investigation, collation, analysis and response as necessary.
CBS should be a routine function for:
the pre-epidemic period (to provide early warning or alerts);
the period during epidemic (to actively detect and respond to cases and deaths);
the post-epidemic period (to monitor progress with disease control activities).
CBS should also include a process to report rumours and misinformation of unusual public
health events occurring in the community
CBS Tasks
The tasks for CBS are in line with IDSR core functions namely:
Using lay simplified case definitions to identify priority diseases, events, conditions or other
hazards in the community.
Participating in verbal autopsies to determine causes of death.
Sending notification, timely and regularly, to the nearest health facility of the occurrence of
unexpected or unusual cases of disease or death in humans and animals for immediate
verification and investigation according to the International Health Regulations (IHR) and in line
with the IDSR strategy.
Involving local leaders in describing disease events and trends in the community.
Supporting health workers during case or outbreak investigation and contact tracing.
Participating in risk mapping of potential hazards and in training including simulation exercises.
Participating in response activities including home-based care, including sensitization of the
community on the adoption of behaviour facilitating the containment of the outbreak.
Using feedback from the CBS Coordinator to take action, including health education and
coordination of community participation.
Verifying if public health interventions took place as planned with the involvement the
community.
Having a forum for feedback to the community on outbreak/event assessment.
Sources of information for community based surveillance
All community based health workers, including traditional birth attendants and school health
masters: these constitute privileged sources of information due to their connections with the local
community and their presence in the field, especially in remote areas where access to primary
health care is scarce.
Community, traditional, youth or religious leaders and civil society: these individuals and groups
may provide informal reports of unusual health events or health risks that they witness in their
communities.
Media: local, national and international media are important sources of information for CBS.
Events such as clusters of human cases, outbreaks or unexpected and unusual deaths may be
covered by local newspapers (printed or available through the Internet) or radio reports before
they are detected and reported by local health services.
Traditional medicine and traditional health practitioners and healers: in some African countries, a
large number of the population depends on traditional medicine for primary health care.
Traditional medicine has been used for thousands of years, and these practitioners may constitute
a valuable source of information.
Alternative medicine (herbalists, for example) complementary medicine and nonconventional
medicine: these include health care practices that are not part of that country's own tradition and
are not integrated into the dominant health care system; they are gaining in 6 popularity and
should be considered as a potential source of health information and contact with them provides
opportunities for encouraging safe practices.
Faith-based Organizations (FBO) and Community-based Organisations (CBO) set ups as source
of information on unusual events.
Families are also sources of information. Community health workers conducting door-to door
activities such as well-baby monitoring can collect information about whether anyone in the
household has been ill.
Preparation and dissemination of disease surveillance report
The following prone diseases are categorized as epidemic and should be reported immediately
(within 24 hours);
Cholera
Diarrhoea with blood (dysentery)
Meningitis
Typhoid fever
Plague
Yellow fever
Other Viral Haemorrhagic fever
The integrated case based surveillance Form MOH 502 should be used to report. In addition, line
list all suspected cases using a health facility line listing form MOH 503.
The following diseases are targeted for eradication in Kenya and should be reported
immediately;
Acute flaccid paralysis (AFP) polio
Measles
Leprosy
Neonatal tetanus
Dracunculiasis (Guinea Worm)
The following diseases are earmarked for weekly IDSR Reporting;
Cholera
Typhoid
Dysentery
Measles
Meningococcal meningitis
Plague
Yellow fever
Viral hemmorhagic fevers
Acute flaccid paralysis
Neonatal tetanus
Malaria
All summarized data should be reported to the national level on weekly basis using Epidemic
Monitoring Form MOH 505.
Other diseases of public importance should be reported on monthly basis;
Diarrhoea with some dehydration in children less than 5 years of age
Diarrhoea with severe dehydration in children less than 5 years of age
Pneumonia in children less than 5 years of age
Severe pneumonia in children less than 5 years of age
Unexplained severe acute respiratory disease (SARD)
New AIDS cases
Tuberculosis
Sexually Transmitted Infections
Types of reporting tools and when to use
IDSR Weeky form to be used for weekly reporting of priority diseases
IDSR-case based, used for diseases that require immediate reporting
IDSR Monthly- used for reporting INDR priority diseases on monthly basis
IDSR Line list- used for line listing cases/deaths reported in an outbreak
1.2.1.4 Learning Activities
Leaning activity Special instructions
Plan disease surveillance
Identify methods of data collection
Carry out disease surveillance
Carry out population screening
Prepare and disseminate disease surveillance
report

1.2.1.5 Self-Assessment
You are provided with the following questions for self -assessment, attempt them and check your
responses
What does the term ‘disease surveillance’ mean?
Distinguish between an epidemic and endemic
Explain the types of epidemiology
Discuss the uses of the information collected during disease surveillance
Discuss the factors that may be associated with increased risk of human diseases

1.2.1.6 Model answers to self-assessment questions

What does the term ‘disease surveillance’ mean?
an information-based activity involving the collection, analysis and interpretation of large
volumes of data originating from a variety of sources.
Distinguish between an epidemic and endemic
Epidemic is the occurrence of a disease in a community of a group of illnesses of similar
nature clearly in excess or beyond normal expectancy while endemic is the habitual
presence of a disease within a given geographical area. It may also refer to the usual
occurrence of a given disease within such an area
Explain the types of epidemiology
descriptive epidemiology: examining the distribution of disease in a population, and
observing the basic features of its distribution
analytic epidemiology: investigating a hypothesis about the cause of disease by studying
how exposures relate to disease
Discuss the uses of the information collected during disease surveillance
serve as an early warning system, identify public health emergencies
Identify high risk populations or areas to target interventions
Evaluate the effectiveness of control and preventative health measures
Monitor changes in infectious agents e.g. trends in development of antimicrobial resistance
Support health planning and the allocation of appropriate resources within the healthcare
system.
Provide a valuable archive of disease activity for future reference.
guide public health policy and strategies
document impact of an intervention or progress towards specified public health
targets/goals
understand/monitor the epidemiology of a condition to set priorities and guide public
health policy and strategies

Discuss the sources of information for community-based surveillance

All community based health workers, including traditional birth attendants and school
health masters: these constitute privileged sources of information due to their connections
with the local community and their presence in the field, especially in remote areas where
access to primary health care is scarce.
Community, traditional, youth or religious leaders and civil society: these individuals and
groups may provide informal reports of unusual health events or health risks that they
witness in their communities.
Media: local, national and international media are important sources of information for
CBS. Events such as clusters of human cases, outbreaks or unexpected and unusual deaths
may be covered by local newspapers (printed or available through the Internet) or radio
reports before they are detected and reported by local health services.
Traditional medicine and traditional health practitioners and healers: in some African
countries, a large number of the population depends on traditional medicine for primary
health care. Traditional medicine has been used for thousands of years, and these
practitioners may constitute a valuable source of information.
Alternative medicine (herbalists, for example) complementary medicine and
nonconventional medicine: these include health care practices that are not part of that
country's own tradition and are not integrated into the dominant health care system; they
are gaining in 6 popularity and should be considered as a potential source of health
information and contact with them provides opportunities for encouraging safe practices.
Faith-based Organizations (FBO) and Community-based Organisations (CBO) set ups as
source of information on unusual events.
Families are also sources of information. Community health workers conducting door-to
door activities such as well-baby monitoring can collect information about whether anyone
in the household has been ill.

Discuss the factors that may be associated with increased risk of human diseases
Host characteristics
Types of agents eg bacteria, protozoa,viruses, fungi,helminthes
Chemical agents i.e poison, alcohol and smoke
Physical agent
These are: trauma, radiation and fire
Nutritional agent
Lack of some of the important food and minerals lead to the risk of developing certain
diseases e.g.
lack of iron –anaemia
lack of vitamin C (scurvy)
Lack of carbohydrate-malnutrition
Lack of protein-Protein Energy Malnutrition
Lack of vitamin B (beriberi)
Excessive amount of some of the micronutrients may also lead to development of a disease
ie haematochromatosis due to iron overload
Environmental factors
temperature: temperature may be conducive for thriving of certain biological agents of
disease
humidity: certain humid levels can be enable transmission of certain biologic agents i.e the
bacteria causing meningitis
altitude: it affects some of the physiological processes of the body
crowding: these translate to poor hygiene practices that lead to transmission of infectious
agent
pollution: generation of harmful fumes from industries can lead to development of
respiratory diseases
1.2.1.6 Tools, Equipment, Supplies and Materials
Computers
Flip charts
Relevant manuals
MOH Reporting tools (MOH 505 IDSR Weekly Epindemic Monitoring form).
Past publications on epidemiology
Analysis software
1.2.1.7 References
Centers for Disease Control and Prevention (2004). Framework for evaluating public health
surveillance systems for early detection of outbreaks: recommendations from the CDC Working
Group. MMWR; 53(RR05);1–11.
Dicker, R. C. (2006). Principles of Epidemiology in Public Health Practice. Cdc, (May),
Glossary of Epidemiology Terms.
Edelstein et al., (2018). Strengthening global public health surveillance through data and benefit
sharing. Emerging Infectious Diseases, 24: p1324.
Heeks R. (2006). Health information systems: Failure, success and improvisatio. International
IDSR National Technical guidelines
IDSR. Standard Case Defitions for Prority Diseases in Kenya
journal of Medicine and Informatics, (75): p125-137.
Omondi et al. (2020). Assessment of Integrated Disease Surveillance Data Uptake in Community
Health Systems within Nairobi County, Kenya
https://eahrj.eahealth.org/index.php/eah/article/view/644/1219
WHO (2014). Integrated disease surveillance and response in the African region-A guide for
establishing community based surveillance

Learning Outcome 2: Carry out population screening

Introduction to the learning outcome

In this unit, you will learn how to carry out population screening. This will involve carrying out
population screening, developing population screening plan, preparing and disseminating
population screening report.
Performance Standard
 Notifiable diseases are identified according to lay case definition
Definitions of terms
False negative: a normal result in a person who does have the condition being tested for.
False positive: an abnormal test result in a person who does not have the condition being tested
for
Health: a state of complete physical, mental, [and] social well-being and not merely the absence
of disease or infirmity
Incidence: number of new cases occurring within a population during a specified time period.
Mortality rate: a measure of the frequency of occurrence of death in a defined population
during a specified interval.
Population: is a distinct group of individuals, whether that group comprises a nation or a group
of people with a common characteristic.
Population at risk: the group of people, healthy or sick, who would be counted as cases if they
had the disease being studied.
Prognosis: a prediction of the likely outcome of a disease condition e.g. recovery, death,
disability
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.
Screening: the process of identifying healthy people who may have an increased chance of a
disease or condition.
Sensitivity: the ability of the screening test to identify people with the condition as positive
(abnormal).
Specificity: the ability of the screening test to identify healthy people as negative (normal).
Screening test: test carried out on someone without symptoms to detect whether they have a
condition or risk factor.
Population screening
Most screening programs attempt to identify the disease process during the incubation phase,
since intervention at this early stage is likely to be more effective than treatment given after the
disease has progressed and become symptomatic.

Objectives of population screening

The immediate objective of a screening test is to classify people as being likely or unlikely of
having the disease while the ultimate objective is to reduce mortality and morbidity Population
screening

Aims of screening programs

The aims of screening programs include:
to reduce mortality by early detection and early treatment of a condition;
to reduce the incidence of a condition by identifying and treating its precursors;
to reduce the severity of a condition by identifying people with the condition and offering
effective treatment; and
to increase choice by identifying conditions or risk factors at an early stage in a life-course when
more options are available.
Carrying out population screening needs assessment
A key feature of epidemiology is the measurement of disease outcomes in relation to
a population at risk. For example, if a general practitioner were measuring how often patients
consult him about deafness, the population at risk would comprise those people on his list (and
perhaps also of his partners) who might see him about a hearing problem if they had one.
Patients who, though still on the list, had moved to another area would not consult that doctor.
They would therefore not belong to the population at risk.
Epidemiological conclusions (on risk) cannot be drawn from purely clinical data (on the number
of sick people seen).
Implicit in any epidemiological investigation is the notion of a target population about which
conclusions are to be drawn. Occasionally measurements can be made on the full target
population.
More often observations can only be made on a study sample, which is selected in some way
from the target population. For example, a gastroenterologist wishing to draw general inferences
about long term prognosis in patients with Crohn’s disease might extrapolate from the
experience of cases encountered in his own clinical practice. The confidence that can be placed
in conclusions drawn from samples depends in part on sample size. Small samples can be
unrepresentative just by chance, and the scope for chance errors can be quantified statistically.
A community health needs assessment serves as the starting point to address a rural community’s
needs and advocate for improvement. The assessment identifies factors that impact a
population’s health and resources available to help resolve these issues. This assessment will
help to identify topics and issues relevant to a community.
Screening patients for preclinical disease is an established part of day to day medical practice.
Routine recording of blood pressure, urine testing, and preoperative chest radiography may all be
regarded as screening activities. Increasingly, screening is now being extended to people who
have not themselves requested medical aid.
Data for determining community needs can be collected through surveys, questionnaires, focus
groups, public meetings, direct observations, and interviews. Secondary data sources such as
demographic data, vital statistics, hospital records, morbidity and mortality reports, and literature
reviews also provide valuable information.
It should be noted that a screening test must be inexpensive and easy to perform. For this reason,
screening test cannot be considered as a valid diagnostic method for a disease.

Screening process
One should think of screening as a sieve where a large group of people is subjected to screening
as illustrated in figure 2.
Figure 2: Illustration of the screening process
Source: www.gov.uk
The sieve represents the screening test and most people pass through it. This means they have a
low chance of having the condition screened for.
The people left in the sieve have a higher chance of having the condition. A further investigation
is then offered to them.
At each stage of the screening process, people can make their own choices about further:
tests
treatment
advice
support
Requirement for a screening programme
The following are the requirements for a screening program
Suitable disease: Focus on diseases which have serious consequences if untreated, detectable
before symptoms appear and have better outcomes if treatment begins before clinical diagnosis.
Suitable test: The test should detect disease during pre-symptomatic phase, should be safe,
accurate, acceptable and cost effective
Suitable program: The screening program should reach appropriate target population, provide
quality control of testing, support good follow-up of positives and be efficient.
Good use of resources: cost of screening tests, cost of follow-up and cost of treatment should be
put into consideration so as to weigh benefits versus alternatives

Qualities of a good screening test

Reliable – get same result each time
Validity – get the correct result
Sensitive – correctly classify cases
Specificity – correctly classify non-cases

 Development of population screening plan

The success of data collection requires careful preparation. The first and often the most difficult
question is “Why am I doing this survey?” When developing a population screening plan, it is
important to first come up with precisely formulated, written objectives. Every survey should be
reasonably sure to give an adequate answer to at least one specific question. This initial planning
requires some idea of the final analysis; and it may be useful at the outset to outline the key
tables for the final report, and to consider the numbers of cases expected in their major cells.
Before planning the detail of a study, it is wise to carry out a library search of the relevant
background publications. Occasionally this may show the answer to the study question without
any need for further data collection; or it may uncover useful sources of published information,
such as the registrar general’s mortality and cancer registry reports, which can form the basis of
an analysis without the requirement for an expensive and time consuming field survey. Even
when survey work remains necessary, experience in earlier related investigations may guide the
design or indicate pitfalls to be avoided.
Preparation for a needs assessment will include consideration of the local circumstances and
background to the commissioning of the needs assessment, identification of stakeholders,
agreeing the scope of the needs assessment, identifying the necessary time and other resources to
carry out the needs assessment and considering what data sources are available.
It is important to identify, involve and engage key stakeholders early on the needs assessment
process to ensure that the work will be the central means of decision-making and resource
allocation and that the output will be fully integrated into the subsequent strategic planning
processes. Some needs assessments focus on specific populations defined by a particular
condition (e.g. cancer), social group (e.g. homeless people, ethnic minority) or setting (e.g.
workplace, school). This often makes it more difficult to identify relevant data sources. However
for high level needs assessment within a health and social care partnership interest may focus on
the whole population, or the adult population, and the sections that follow take this approach.

Carrying out population screening

Every screening programme needs to set the parameters for how it will operate. These should be
based on the best evidence, feasibility and cost– effectiveness. These parameters include: who
should be invited; how often; what information people should be given to make an informed
choice; the threshold for the test and its sensitivity, specificity and positive predictive value; and
what diagnostic procedures and treatments should be used.
Choice of examination methods
The overriding need in an epidemiological survey is to examine a representative sample of
adequate size in a standardized and sufficiently valid way. This determines the choice of
examination methods and the points where these differ from those of clinical practice. Methods
must be acceptable, and if possible noninvasive, or else cooperation suffers and the study group
becomes unrepresentative. They must be relatively cheap and quick, or not enough subjects can
be examined: with fixed resources the need for detail conflicts with the need for numbers. Most
important of all, methods and observers must be capable of rigorous standardization; even if this
excludes the benefits of clinical judgment.
Ethics of population screening
Since population screening is conducted on otherwise healthy people, healthcare professionals
have to ensure individuals receive:
guidance to help make informed choices
support throughout the screening process
Screening expectations
It is important to have realistic expectations of what a screening programme does.
Screening can:
save lives or improve quality of life through early identification of a condition
reduce the chance of developing a serious condition or its complications
Screening does not guarantee protection. Receiving a low chance result does not prevent the
person from developing the condition at a later date.
In any screening programme there are false positive and false negative results:
false positive: wrongly reported as having the condition
false negative: wrongly reported as not having the condition

 Preparation and dissemination of population screening report

Population screening report should show the yield of the screening service, which is mostly
measured by the number of cases identified whose prognosis is improved as a result of early
detection. This should be related to the total number of tests performed.
The report should also include the costs, in terms of staff and facilities, of screening and making
the confirmatory diagnoses.
Follow this video link to learn more about population screening
https://www.youtube.com/watch?v=qeV42ITpbpU
1.2.1.4 Learning Activities
Leaning activity Special instructions
Carry out population needs assessment
Develop a population screening plan
Carry out population screening
Prepare and disseminate population screening
report

1.2.1.5 Self-Assessment
You are provided with the following questions for self -assessment, attempt them and check your
responses
What is the difference between a false positive and a false negative in population screening?
The test carried out on someone without symptoms to detect whether they have a condition or
risk factor is known as -______________
What do population screening programmes aim at?

1.2.1.6 Model answers to self-assessment questions

What is the difference between a false positive and a false negative in population screening?
A false positive is an abnormal test result in a person who does not have the condition being
tested for while a false negative is a normal result in a person who does have the condition
being tested for.
The test carried out on someone without symptoms to detect whether they have a condition or
risk factor is known as -______________ Screening test
What do population screening programmes aim at?
to reduce mortality by early detection and early treatment of a condition;
to reduce the incidence of a condition by identifying and treating its precursors;
to reduce the severity of a condition by identifying people with the condition and offering
effective treatment; and
to increase choice by identifying conditions or risk factors at an early stage in a life-course
when more options are available.
1.2.1.7 Tools, Equipment, Supplies and Materials
Computers
Flip charts
Relevant manuals
MOH Reporting tools (MOH 505 IDSR Weekly Epindemic Monitoring form).
Past publications on epidemiology
Analysis software
1.2.1.8 References
Austoker J. Gaining informed consent for screening. Br Med J. 1999;319:722–3.
Dicker, R. C. (2006). Principles of Epidemiology in Public Health Practice. Cdc, (May),
Glossary of Epidemiology Terms.
Kate, L., & Evers-kiebooms, G. (2003). Population genetic screening programmes : principles ,
techniques , practices , and policies. European Journal of Human Genetics, 11, 49–87.
https://doi.org/10.1038/sj.ejhg.5201113
Public Health England (2013). NHS population screening explained
https://www.gov.uk/guidance/nhs-population-screening-explained
Raffles A, Mackie A, Muir Gray JA. Screening: evidence and practice. 2nd ed. Oxford: Oxford
University Press; 2019.
WHO. (2020). Screening programmes : a short guide.
https://apps.who.int/iris/bitstream/handle/10665/330829/9789289054782-eng.pdf
Zorzela L, Loke YK, Ioannidis JP, Golder S, Santaguida P, Altman DG et al. PRISMA harms
checklist: improving harms reporting in systematic reviews. BMJ. 2016;352:i157.

Learning outcome 3: Monitor disease occurrence

Introduction to the learning outcome

In this unit, you will learn how to monitor disease occurrence. This will involve identifying
notifiable disease, notifying occurrence of disease, determining planning for disease surveillance,
planning community surveillance, determining preventive measures for disease and carrying out
reporting and referral of cases.
Performance Standard
i. Notifiable diseases are identified according to lay case definition
ii. Occurrence of disease is notified based on lay case definition
iii. Planning for disease surveillance is determined according to standard procedures
iv. Community surveillance is planned based on the magnitude of disease occurrence
v. Preventive measures for diseases are determined based on standard procedures
vi. Reporting and referral of cases is carried out according to standard procedures
Definitions of terms
Data: a collection of facts from which conclusions may be made

Notification of disease occurrences

Planning for disease surveillance
Notifiable diseases in Kenya
A notifiable disease is any disease that is required by law to be reported to government
authorities. The collation of information allows the authorities to monitor the disease, and
provides early warning of possible outbreaks. In the case of livestock diseases, there may also be
the legal requirement to destroy the infected livestock upon notification. Many governments
have enacted regulations for reporting of both human and animal (generally livestock) diseases.
This usually happens during pandemics. The World Health Organization's International Health
Regulations 1969 require disease reporting to the organization in order to help with its global
surveillance and advisory role. The current (1969) regulations are rather limited with a focus on
reporting of three main diseases: cholera, yellow fever and plague.
The revised International Health Regulations 2005 broadens this scope and is no longer limited
to the notification of specific diseases. Whilst it does identify a number of specific diseases, it
also defines a limited set of criteria to assist in deciding whether an event is notifiable to WHO.
Examples: Plague, Cholera, Meningitis & SAR

Use of Epidemiology to Establish Cause of a Disease

In trying to establish the cause of a disease main steps are involved
Step 1 involves determining whether there is an association between a factor
To establish causal relationships and epidemiologic study of characteristics of groups of
individuals
2.We then derive an appropriate inference regarding possible causal relationship pattern of
association that have been used in order to identify causes of disease eg cohort study and case
control study.
In trying to identify the cause of a disease one must consider disease determinants.
Disease determinants are of many types including:
biological determinants: These are-age, gender and genetic make-up
behavioral determinants: These include lifestyle and nutrition
environmental determinants -heat, radiation
social determinants: social economic status, occupation, race, ethnicity
Exposure-is the other factor to pay attention in choosing study design. It’s a substance,
phenomenon or even that can cause or protect from disease. Exposure can be measured by use of
instrument i.e.
Questionnaires
Interviews
Biochemical analysis of biological materials
Physical and chemical analysis of environment.

Epidemiology study types

 Descriptive
Observational
Epidemiology
Analytic
study types
Experimental

In an experimental study, the investigators can control certain factors within the study from the
beginning. An example of this type is a vaccine efficacy trial that might be conducted by the
National Institutes of Health. In such a trial, the investigators randomly control who receives the
test vaccine and who does not among a limited group of participants; they then observe the
outcome to determine if it should to be used more widely.
In an observational study, the epidemiologist does not control the circumstances. These studies
can be further subdivided into descriptive and analytic.
Descriptive epidemiology is the more basic of these categories and is fundamental to what
epidemiologists do. In a descriptive study, the epidemiologist collects information that
characterizes and summarizes the health event or problem.
In the analytic study, the epidemiologist relies on comparisons between different groups to
determine the role of different causative conditions or risk factors

Data sources and Collection methods

Source Method Example
Individual persons Questionnaire Foodborne illness outbreak
Survey
Environment Samples from the Collection of water from area
environment streams
Sensors for environmental Air quality ratings
changes
Healthcare providers Notifications to the health Report cases of meningitis to
department if cases of certain health department
 diseases are observed
Non-health related sources Sales record Cigarette sales
Court records Intoxicated driver arrests

Classes and categories of data

Qualitative data
describes meaning rather than draw statistical inferences
relativity is not quantifiable
also referred to as nominative data
Quantitative data
deals with numbers and frequencies
further divided into discrete and continuous data
Discrete
This is based on counts
Only a finite number of values is possible
values cannot be meaningfully subdivided.
Analysed thru non-parametric methods
Parametric methods apply when transformed
Continuous data
measured on a continuum or scale
value and accuracy depends on precision of measurement.
Analysed thru parametric methods
Prevalence
ratio of the number of diseased subjects at certain point in time and the total number of animals
at risk including the diseased at that time.
No. of subjects having an event at a specific time
Prevalence (P) =
Population of animals at risk at that point in time
Incidence
describes number of new cases of a disease in a population over a specified period of time. thus
describes the change per unit time among subjects at risk.
Two incidence measures must be differentiated:
Cumulative incidence (CI):
direct estimate of the probability of experiencing the event of interest during the full duration of
the time period.
defined as the ratio between number of subjects that contract a disease in a certain period and the
number of healthy subjects at risk in the population at the start of that period.
Incidence rate or incidence density rate (IR)
describes average speed at which the event of interest occurs per unit animal/human time at risk
denominator = sum of time periods of all individual animals at risk of acquiring the event of
interest.
It is measured in animal/human time:
1 animal year is 1 animal at risk for one year or
12 animals being at risk for one month (1/12 of a year) or
365 animals being at risk for one day (1/365 of a year)
IDR: calculated when population studied is very dynamic. Animals are added/withdrawn from
the population.
IDR: difficult to assemble - details lacking.
Number of new cases that occur in a population during a period of time
Incidence rate (IR) =
total animal time at risk of getting the event of interest
Study Designs
There are three study designs which are commonly used in epidemiology;
cross-sectional,
cohort, or
case-control approach.
In crosss-sectional study, subjects are selected because they are members of a certain population
subset at a certain time. A cross-sectional study is similar to a survey in that it provides a
snapshot of the population at a point in time. Using this study, the epidemiologist defines the
target population, then collects data from the population or a subset of the population at one
specific point in time.
In a cohort study, the epidemiologist selects a population, then categorizes each person by
whether he or she was exposed to one or more risk factors of interest. Participants are followed
over time to determine if a disease or condition develops
A case-control study compares one group who has a disease or health condition, referred to as
case-patients, with a group that does not, referred to as control subjects.
The epidemiologist then works backward from the illness or health condition. Case-patients and
control subjects are compared for the presence or absence of one or more specific exposures or
risk factors.
Theoretical studies
there is use of models to study association of risk factors with given outcomes
In this case, models employed include:
Conceptual models
Mathematical models
Simulation
Advantages of cohort study
Can establish population-based incidence
- Accurate relative risk (risk ratio) estimation
- Can examine rare exposures (asbestos > lung cancer)
- Temporal relationship can be inferred (prospective design)
- Time-to-event analysis is possible
- Can be used where randomization is not possible
- Magnitude of a risk factor’s effect can be quantified
- Selection and information biases are decreased
- Multiple outcomes can be studied
(smoking > lung cancer, COPD, larynx cancer)
Disadvantages of cohort studies
-Lengthy and expensive
- May require very large samples
- Not suitable for rare diseases
- Not suitable for diseases with long-latency
- Unexpected environmental changes may influence the association
- Nonresponse, migration and loss-to-follow-up biases
- Sampling, ascertainment and observer biases are still possible
Sampling strategy and sample calculation
Non-probability sampling:
Methods that do not use formal random techniques to identify sampling units to be included in
the sample.
Examples:
Convenient sampling
Purposive sampling
Judgment sampling
Non-probability sampling produce bias
Probability/Random sampling
This satisfies the following properties:
Every member of the population has a known probability of being included in the sample
The sample is drawn by some method of random selection consistent with these probabilities
Selection probabilities are considered when making estimates from the sample
Examples of random sampling
Simple random sampling
Systematic random sampling
Stratified random sampling
Cluster sampling
Multistage sampling
Sampling unit
Items, locations, people, that will be selected individually by a sampling method. They may be
primary, secondary or tertiary units e.g. Province, village, farm.
Sampling frame
Usually a list that contains all the sampling units of a population
Learning Activities
Leaning activity Special instructions
Identify notifiable diseases
Notify occurrence of disease
Determine planning for disease surveillance
Plan community surveillance
Determine preventive measures for diseases
Carry out reporting and referral of cases

Self-Assessment
You are provided with the following questions for self -assessment, attempt them and check your
responses
What are the sources of error in epidemiologic studies?
A community health worker is carrying out a study on the sleep patterns of primary school pupils
but does not provide any intervention. What type of study is this?
A study of heart disease comparing a group who eats healthy foods and exercises regularly with
one who does not in an effort to test association is classified as_____________
A study to describe the eating habits of adolescents aged 13–18 years in Community Z is
classified as ______________
After attending a family dinner offering a meal composed of grilled chicken, rice, mashed potato
and ice cream, 9 family members of attendance developed gastroenteritis. All attainders were
interviewed. Use the data in the summary case histories to determine the food item most likely to
have caused this outbreak
1.2.1.6 Model answers to self-assessment questions
What are the sources of error in epidemiologic studies?
Answer:
Random error
Bias
Confounding
Effect Modification
Reverse Causation
A community health worker is carrying out a study on the sleep patterns of primary school pupils
but does not provide any intervention. What type of study is this?
Answer:
Observational study
A study of heart disease comparing a group who eats healthy foods and exercises regularly with
one who does not in an effort to test association is classified as_____________
Answer:
Analytical study
A study to describe the eating habits of adolescents aged 13–18 years in Community Z is
classified as ______________
Answer
Descriptive study

After attending a family dinner offering a meal composed of grilled chicken, rice, mashed potato
and ice cream, 9 family members of attendance developed gastroenteritis. All attainders were
interviewed. Use the data in the summary case histories to determine the food item most likely to
have caused this outbreak

Answer:
1.2.1.7 Tools, Equipment, Supplies and Materials
Computers
Flip charts
Relevant manuals
MOH Reporting tools (MOH 505 IDSR Weekly Epindemic Monitoring form).
Past publications on epidemiology
Analysis software
1.2.1.8 References
1. Dicker, R. C. (2006). Principles of Epidemiology in Public Health Practice. Cdc, (May),
Glossary of Epidemiology Terms.
2. Ahlbom A, Norell S. Introduction to modern epidemiology, 2nd edn. Chestnut Hill,
Massachusetts: Epidemiology Resources, 1990.

Learning Outcome 4: Utilize epidemiology data

Introduction to the learning outcome

In this unit, you will learn how to utilize epidemiology data. This will involve collating
epidemiology data, disseminating epidemiology data, developing action plan, controlling
community diseases and determining acceptable health interventions.
Performance Standard
i. Epidemiology data is collated as per the set guidelines
ii. Epidemiology data is disseminated as per the stipulated procedures
iii. Action plan is developed according to set guidelines
iv. Community diseases are controlled based on epidemiological data analysis outcomes
v. Acceptable health interventions are determined and applied in accordance with
epidemiological data findings
Definitions of terms
Community: A group of people with a common characteristic or interest living together within a
larger society
Community diagnosis: is a comprehensive assessment of health status of the community in
relation to its social, physical and biological environment
Health Indicators: Variables used for the assessment of community health.
Health promotion: any combination of educational, organizational, economic, and
environmental supports for behavior and conditions of living conducive to health
Epidemiological information is used to plan and evaluate strategies to prevent illness and as a
guide to the management of patients in whom disease has already developed.

Community health diagnosis

Community health deals with all the services that is aimed at protecting the health of the
community
 Preventive
 Promotive
 Curative
 Rehabiltative

Objectives of community diagnosis

Analyze the health status.
Evaluate the health resources, services, and systems of care.
Assess attitudes toward community health services and issues.
Identify priorities, establish goals, and determine courses of action to improve health status.
Establish epidemiologic baseline for measuring improvement over time.
Steps in community health diagnosis
Characteristics of health indicators
Valid: Measure what they are supposed to measure.
Reliable and objective: the same if measured by different people in similar circumstances
Sensitive: to changes in the situation concerned,
Specific: reflect changes only in the situation concerned
Feasible: Have the ability to obtain data needed
Relevant: Contribute to the understanding of the phenomenon of interest.
Classification of health indicators
Mortality Social and mental health
Morbidity Environmental
Disability rates Socio-economic
Nutritional status Health policy
Health care delivery Quality of life
Utilization rates

Mortality indicators include;

Mortality rates
Crude death rates
Specific death rates
Expectation of life
Infant mortality rate
Maternal mortality rate
Proportionate mortality rate
Case fatality rate
Morbidity indicators include;
Incidence and prevalence
Notification rate
Attendance rates-out-patient clinics and health centers
Admission and discharge rates
Hospital stay duration rates
Disability indicators
Disability rates
No. of days of restricted activities
Bed disability days
Work/school loss days within a specified period
Expectation of life free of disability
Nutritional indicators
Nutritional status
Anthropometrics measurements
Height of children at school entry
Prevalence of low birth weight
Clinical surveys
Health Care Delivery Indicators
Health Care Delivery Indicators - Reflect the Equity / Provision of health care
Physician / Population ratio
Physician / Nurse ratio
Population / Bed ratio
Population / Health center
Utilization Indicators
Health care utilization Rates - Extent of use of health services - Proportion of people in need of
service who actually receive it in a given period
Proportion of infants who are fully immunized in the 1st year of life. “immunization coverage”.
Proportion of pregnant women who receive ante-natal care.
Hospital-Beds occupancy rate.
Hospital-Beds turn-over ratio
Social/Mental Health Indicators
Indicators of Social and Mental Health - Valid positive indicators does not often exist - Indirect
measures are commonly used
Suicide & Homicide rates
Road traffic accidents
Alcohol and drug abuse.
Environmental Indicators
Environmental health Indicators - Reflect the quality of environment
Measures of Pollution
Proportion of people having access to safe water and sanitation facilities
Vectors density
Socio-economic Indicators
Socio-economic Indicators - Is not a direct measure of health status. - For interpretation of health
care indicators.
Rate of population increase
Per capita GNP
Level of unemployment
Literacy rates – females
Family size
Housing condition e.g. No. of persons per room
Health Policy Indicators
Health Policy Indicators - Allocation of adequate resources.
Proportion of GNP spent on health services.
Proportion of GNP spent on health related activities.
Proportion of total health resources devoted to primary health care

The process of community diagnosis involves the following steps:

Collecting background information of various communities
Selecting a target community
Initial planning
Determine the objectives
Define the study population
Scope of the survey
Selection of appropriate indicators
Selecting appropriate time of the year
Identifying resources
Sampling: Selection of study population from reference population; probability and non-
probability sampling
Developing tools and techniques
Household questionnaires
Anthropometric instruments
Observation checklist
Key-informant guidelines
In depth interview guidelines (patients visiting health facility)
FGD guidelines
Entry to the community, rapport building, social mapping
Collecting the data
Records review
Surveys & Observations
Interviews
Participant observation

Sources of Data:
Routine reporting from health facilities
Surveillance: active, passive.
Screening
Special surveys
Rapid surveys
Contact tracing
Vital registration
A combination of several methods
Data entry and processing: Data validation, data sorting and sequencing, summarizing,
computing etc.
Data analysis and interpretation: data can be displayed in graphs, charts etc
Need identification: determining observed needs and felt needs, and thn finalizing the real needs
of the community and ultimately identifying the necessary measures to solve them.
Prioritizing needs with community people: Not all needs can be met. The health needs of the
community should be prioritized as follows;
Equity
Disease burden
Cost effectiveness
Community interest
Existing capacity
National priority
Sustainability
Time of evaluation
Conducting Micro-Health project and evaluation
Dissemination: Community presentations, final report sharing to community and concerned
authorities
Follow up: Since community diagnosis is not a one-off project, it should not be conducted at
regular intervals to allow the health status of the community to be continuously improved.

Determination and control of community diseases

Outbreak investigation
Ten steps are involved in outbreak investigations, including
Step 1 — Establishing the existence of an outbreak. Use data from data sources
Step 2 — Preparing for field work. Research the disease; Gather supplies and equipment;
Arrange travel
Step 3 — Epidemiologists ensure that the problem is accurately diagnosed by speaki with
patients and reviewing laboratory findings and clinical test results.
Review laboratory findings and clinical test results
Step 4 — defining and identifying cases. This entails establishing a case definition by using a
standard set of criteria. Four components typically are included in a case definition, including
1. Clinical information about the disease — What signs and symptoms have been observed?
2. Characteristics about the persons who are affected — Do any commonalities exist among
those who have been ill?
3. Information about the location or place — Where are the affected persons located?
4. Specification of time during which the illness onset occurred — What date or time did the
illness begin to occur, and what was the symptom duration?
During an outbreak, the case definition can evolve, typically becoming more specific as more
information becomes available.
To assist epidemiologists in identifying early Legionnaires’ disease cases, public health nurses
made rounds at local Philadelphia hospitals to gather data about those who became ill to verify
the diagnosis. Meanwhile, laboratory samples and clinical examinations were tested and
reviewed.
After the initial case definition was established, health care facilities — such as doctors’ offices,
clinics, laboratories, and hospitals — were contacted to request that any observations of illnesses
matching the case definition be reported.
Step 5 — Using descriptive epidemiology. Step 5 involved using descriptive epidemiology to
describe Legionnaires’ disease and orient the data by identifying
what,
who,
where,
when,
why, and
how.
After these were identified, the epidemiologist proceeded to study the
dates,
times,
places, and
persons.

Step 6 — Develop a focused hypothesis

Step 7 — Evaluate the hypothesis for validity
Step 8 — Refine the hypothesis as needed
Step 9 — Implement control and prevention measures
Step 10 — Communicate findings
Determine who needs to know
Determine how information will be communicated
Identify why the information needs to be communicated

Levels of disease prevention include primary, secondary and tertiary levels discussed as follows;
Primary health care
It’s a service that prevents disease thus promoting health of a community. These means treating a
disease before it has occurred. Resources for the development and running of the services of
health care are limited and thus prevention of diseases saves on economy to make that money
available for other priorities ie education.
The current depressed economic situation in the sub-Saharan Africa has placed a strain on health
service and the challenge is how to use what use whats available so that everyone benefits.
Emphasis has been placed on the prevention of disease and on extensive health service to all
community. The Alma Atta International Conference in primary health care provides a great
stimulus with this effort. The Alma Atta declaration listed the following key element of primary
health care.
element education concerning prevailing health problems and methods of preventing and
controlling them
promotion of food supply and proper nutrition
adequate supply of safe water and basic sanitation
Maternal and child health care including family planning. Immunization against major infectious
disease
provision of essential drugs
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)
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.
Primary prevention therefore is an action taken on people who are health ill. e.g. immunization
against certain diseases ensures that the diseases never occur in that person in case of exposure to
certain disease reduces the risk of developing a condition e.g. smoking as a habit can be reduced
by giving health education to prevent most of the lung cancer cases.
The challenge of primary health care is for the many diseases prevention of which don’t have a
defined biological, clinical and epidemiological data.
Secondary prevention
Secondary prevention happens with e 'Early detection and intervention, preferably before the
condition is clinically apparent, and has the aim of reversing, halting, or at least retarding the
progress of a condition. 'It sometimes happens that a patient first becomes aware of a disease
when it is already too late for it to be successfully treated.‘
Therefore, secondary prevention involves identifying people in whom a disease has already
began but who has not yet developed clinical signs and symptoms of the illness. These period in
the natural history of a disease is called preclinical phase. Once a person develops clinical signs
or symptoms it is generally assumed that they seek medical care. The aim of secondary
prevention is to detect the disease early than it would have been detected with usual care. This is
efected by screening in the hope that treatment would be easier and more effective.
Example
Cases of breast cancer which can be detected by mammography. The rationale is that secondary
prevention will provide intervention measures that will reduce mortality or complication of
diseases and thus use less costly treatment. Secondary prevention thus involve screening,
surveillance or prophylaxis.
Tertiary prevention
Tertiary does prevent complication with those who have already developed symptoms of an
illness. These are people who are in clinical phase of their illness. This level of prevention
focuses on 'Minimizing the effects of disease and disability by surveillance and maintenance
aimed at preventing complications and premature deterioration. It is generally achieved through
prompt and appropriate treatment. It also incorporates approach such as physical therapy. It
reduces disability and provides rehabilitation (medical and social rehabilitation) for those with
disability.
CONTROL AND ERADICATION OF DISEASES
Control is the ongoing operation or programme aimed at reducing incidence of prevalence of
such conditions such as HIV/AIDS is controlled by WHO/NASCOP.
EPI-Extended Programme Immunization means a group targeting immunization for all.
Eradication is the termination of immunization of infection by exterminating infectious agents
through surveillance and containment. This ensures an attainment of a status whereby no further
cases occur ie small pox was eradicated in 1970’s.

Determination of acceptable health interventions

Learning Activities
Leaning activity Special instructions
Collate epidemiology data
Disseminate epidemiology data
Develop action plan
Control community diseases
Determine acceptable health interventions

Self-Assessment
You are provided with the following questions for self -assessment, attempt them and check your
responses
Identify the levels of disease prevention
What are the sources of data for community diagnosis?
Outline the indicators for morbidity in epidemiological studies
Explain the steps involved in the process of community diagnosis
In 2018, during a regional Convention in Kenya, 10 attendees had died of apparent heart attacks
by August 1. Dr. Claire contacted the Kenya Department of Health after realizing she had treated
4 of those 10 attendees. What is the first step the Kenya Department of Health should have
followed?
CDC then launched an investigation. However, no effective communication existed between
scientists in the field interviewing patients and those in the laboratory who were testing
specimens.
As a first step in stopping this outbreak, what should the team have done to identify persons who
were part of the outbreak?

Model answers to self-assessment questions

Identify the levels of disease prevention
Primary level
Secondary level
Tertiary level
What are the sources of data for community diagnosis?
Routine reporting from health facilities
Surveillance: active, passive.
Screening
Special surveys
Rapid surveys
Contact tracing
Vital registration
A combination of several methods
Outline the indicators for morbidity in epidemiological studies
Incidence and prevalence
Notification rate
Attendance rates-out-patient clinics and health centers
Admission and discharge rates
Hospital stay duration rates
Explain the steps involved in the process of community diagnosis
Collecting background information of various communities
Selecting a target community
Initial planning
Determine the objectives
Define the study population
Scope of the survey
Selection of appropriate indicators
Selecting appropriate time of the year
Identifying resources
Sampling: Selection of study population from reference population; probability and non-
probability sampling
Developing tools and techniques
Household questionnaires
Anthropometric instruments
Observation checklist
Key-informant guidelines
In depth interview guidelines (patients visiting health facility)
FGD guidelines
Entry to the community, rapport building, social mapping
Collecting the data
Records review
Surveys & Observations
Interviews
Participant observation
Data entry and processing: Data validation, data sorting and sequencing, summarizing,
computing etc.
Data analysis and interpretation: data can be displayed in graphs, charts etc
Need identification: determining observed needs and felt needs, and thn finalizing the real
needs of the community and ultimately identifying the necessary measures to solve them.
Prioritizing needs with community people
In 2018, during a regional Convention in Kenya, 10 attendees had died of apparent heart attacks
by August 1. Dr. Claire contacted the Kenya Department of Health after realizing she had treated
4 of those 10 attendees. What is the first step the Kenya Department of Health should have
followed?
Answer:
Establish the existence of an outbreak
CDC then launched an investigation. However, no effective communication existed between
scientists in the field interviewing patients and those in the laboratory who were testing
specimens.
As a first step in stopping this outbreak, what should the team have done to identify persons who
were part of the outbreak?
Answer:
Establish a case definition to identify cases

Tools, Equipment, Supplies and Materials

Computers
Flip charts
Relevant manuals
MOH Reporting tools (MOH 505 IDSR Weekly Epidemic Monitoring form).
Past publications on epidemiology
Analysis software
References
Dicker, R. C. (2006). Principles of Epidemiology in Public Health Practice. Cdc, (May),
Glossary of Epidemiology Terms.
World Health Organization. City Health Profiles: how to report on health in your city.
ICP/HSIT/94/01 PB 02. Available at: www.euro.who.int/document/wa38094ci.pdf
Garcia P, McCarthy M. Measuring Health: A Step in the Development of City Health Profiles.
EUR/ICP/HCIT 94 01/PB03. Available at: www.euro.who.int/document/WA95096GA.pdf
Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of
pneumonia. New Engl J Med 1977;297 1189–97.