Fundamental of epidemioloy

By/ MahmoudShaqria
‫شقريه‬ ‫محمد‬ ‫محمود‬

Educational objectives:
At the end of this lecture each master degree
student will be able to:
1-Define epidemiology.
2-define the following term:
Incidence
Prevalence: (Case-fatality rate (CFR)
Endemic
Epidemic
Pandemic
Health indicator
Vital statistics

3-list Function of epidemiology.
4-Discuss modes of epidemiologic investigation.
5-Discuss system of surveillance data.
6-Mention source of data.
7-Identify source of error.

Out lines:
1-Introduction.
2-Definitione
2-definition of the following term:
Epidemiology
Incidence
Prevalence: (Case-fatality rate)(CFR)
Endemic
Epidemic
Pandemic
Health indicator
Vital statistics

3- Function of epidemiology
4- Modes of epidemiologic investigation.
5- System of data surveillance.
6- Source of data.
7- Source of error.

Introduction
 Epidemiology is both a field of research to advance scientific
understanding and also of application of knowledge to control
disease and advance public health, a (primarily observational)
science and a public health profession. Thus, epidemiologists
conduct research and also work to control and prevent disease;
they are scientists and engineers.

 Epidemiologic investigation is problem-oriented and tends
toward applied research
 It‘s a basic science of public health , though then be
prepared to define ―public health‖.
 ―‘Epidemiology‘ comes from the Greek epic (among,
upon), demos (people), and logy (study).

Definition of epidemiology:
 Epidemiology is the study of the distribution and
determinants of health in populations and the
application of this study to improve health.

Epidemiology Terms and
Definitions

Incidence:
 number of new cases that occur in a population during a
certain time period; can also be called an attack rate
(especially when used during an epidemic)
Prevalence:
 number of cases that exist in a population during a certain
time period
(Case-fatality rate (CFR):
 The proportion of cases that die from a particular
disease/health issue (number of cause-specific deaths over
number of incident cases)

Endemic:
 The usual incidence or prevalence of a certain disease in a
population; the baseline or expected number of cases in a
population; can vary between geographic areas
Epidemic:
 when the number of cases of a disease rises above endemic
levels in a specific area or among a specific population over a
particular time period
Pandemic:
 an epidemic occurring over several countries or continents and
usually affecting a large proportion of the population

Health indicator:
 measurement that reflects the health state of people in a
population; infant mortality rate is often used as a health
indicator of entire countries because it is influenced by
multiple factors such as maternal health, environmental
conditions, education levels, and access to medical care
Vital statistics:
 information about births, marriages, divorces, and deaths in a
population that comes from their systematic registration by
local health authorities

1. Discover the agent, host, and environmental factors that
affect health.
2. Determine the relative importance of causes of illness,
disability, and death, in order to establish priorities for
research and action.
3. Identify those sections of the population which have the
greatest risk from specific causes of ill health
4. Evaluate the effectiveness of preventive and therapeutic
health programs and services in improving the health of the
population

5. Study the natural history of disease from its precursor states
through its manifestations and clinical course
6. Conduct surveillance of disease and injury occurrence in
populations and of the levels of risk factors .
7. Investigate outbreaks (e.g., hospital-acquired infections,
disease clusters, food-borne and water-borne infections) to
identify their source and controlling epidemics (e.g., measles,
rubella, coronary heart disease, overweight)

Modes of epidemiologic
investigation

 Epidemiologic investigations are characterized
as either descriptive or analytic.
Descriptive epidemiology::
 Descriptive epidemiology describes the health conditions and
health-related characteristics of populations, typically in
terms of person, place, and time.

 This information serves as the foundation for studying
populations.
 It provides essential contextual information with which to
develop hypotheses, design studies, and interpret results.
 Surveillance is a particular type of descriptive epidemiology, to
monitor change over time.

Analytic studies:
 Analytic studies typically involve the testing of hypotheses,
which in turn may arise from ; Case reports ; Case series ;
Laboratory studies .

The Application of Surveillance System Data

The Application of Surveillance
System Data
 Outbreak investigation is one of the most important
components of surveillance and detection systems.
 Sensitive surveillance systems can detect when abnormal
health events are occurring, and can enable health authorities
(such as local health departments, the CDC, and the WHO) to
know when their investigation and intervention is necessary

Prepare for fieldwork
 The investigator should make sure to collect all relevant
information concerning the reported outbreak, bring all
materials (like lab equipment for taking samples), and
bring all safety equipment needed to protect him or her
from harm in the field.

Establish the existence of an outbreak
 To avoid wasting resources, it is important that surveillance
and detection systems analyze the reported rise in health
events to make sure that an outbreak is actually occurring.
 The amount of cases reported should be significantly
higher than normal or endemic levels in the population

Verify the diagnosis :
 As a certain pathogen or disease is implicated in the outbreak,
it is important to make sure that it has been correctly
identified.
 Things to consider are:
has an error in the laboratory been made?
Do the laboratory results and clinical findings in the field
match up?

Define and identify causes :
 Establishing a working case definition is a crucial step in an outbreak
investigation.
 When interviewing and collecting data from cases, the following data
should be recorded for each person:
identifying information (name and contact information),
demographic
information (name, age, sex, race, income, etc.), clinical
information
(symptoms, medical measurements, time onset of symptoms), and
potential risk factors for (and exposures to) the disease (e.g. ate at a
specific restaurant).
 All of this information describing the cases is usually organized into a table

Evaluate hypotheses
 Investigators can evaluate their hypotheses in many different
ways, depending on what type of outbreak is occurring.
 This stage usually involves a visit to the hypothesized source
location, along with taking samples and conducting
laboratory tests.
 It may also involve analytic epidemiologic studies.

Implement control and prevention measures
 Timing of this step is crucial during an outbreak
investigation.
 While an investigator wants to make sure that he or she
intervenes in a timely manner to prevent further disease
transmission, he or she also wants to make sure that the
hypothesis is correct and does not create unnecessary fear or
panic among the public.

Communicate findings
 It is important in the public health field that all findings and
conclusions are reported during and after an investigation.
 Reports need to be communicated to the parties involved,
including local health authorities, cases.

Sources of data
 Since epidemiology studies populations in their ordinary
environments, there are many kinds of data that are relevant, and
obtaining them can be logistically challenging and expensive.
Sources of data for epidemiologic studies include:
1-Aggregate data Vital statistics (birth rates, death rates,)
2- Demographic, economic, housing, geographical,
3- Workplace monitoring systems
4- Environmental monitoring systems (e.g., air pollution
measurements)
5- Production and sales
6-Medical record
7-questionnair

Sources of error:
The challenge of data quality in epidemiology is to control the
many sources of error in observational studies of human
populations.
The best understood and most quantifiable is:
1- Sampling error, the distortion that can occur from the ―luck
of the draw‖ in small samples from a population.
2- Selection bias, where the study participants are not
representative of the population of interest.

Referance
Davies, Huw Talfryn Oakley; Iain Kinloch Crombie, Manouche Tavakoli. When
can odds ratios
mislead? BMJ 1998;316:989-991.
Deubner, David C., Herman A. Tyroler, John C. Cassel, Curtis G. Hames, and
Caroline Becker.
Attributable risk, population attribution risk, and population attributable fraction
of death associated
with hypertension in a biracial population. Circulation 1975;52:901-908
Freeman, Jonathan; George B. Hutchison. Duration of disease, duration
indicators, and estimation
of the risk ratio. Am J Epidemiol 1986; 124:134-49. (Advanced)
Gladen, Beth C. On graphing rate ratios. Am J Epidemiol 1983; 118:905-908.
Greenland, Sander. Relation of probability of causation to relative risk and
doubling dose: a
methodologic error that has become a social problem. Am J Public Health 1999
(August)

Fundamental of epidemioloy

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