1. بسم الله الرحمن الرحيم
“Epidemiology"
Introduction

2. “Epidemiology" is simply the study of health and disease in populations.
It’s a basic science of public health. The discipline of epidemiology is
the principles of studying the occurrence of illness and related states
and events among populations .”
" Epidemiology " comes from the Greek:
epi… (among, upon),
demos…. (people), and
logy ….(study)

3. “The study of the distribution and determinants of health related
Definition:
“The study of the distribution and determinants of health related
states and events in populations, and the application of this
study to control health problems” [John M. Last, Dictionary of
Epidemiology]).

4. The functions of epidemiology may be summarized as:
1-Discover the agent, host, and environmental factors that affect health, in
order to provide the scientific basis for the prevention of disease and injury
and the promotion of 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, in order that the indicated action may be directed
appropriately.
4-Evaluate the effectiveness of preventive and therapeutic health programs and
services in improving the health of the population.

5. 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 – passive
(receive reports), active (poll practitioners, conduct surveys).
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).

6. Characteristics of epidemiology:
“Epidemiology” focuses on diseases among human populations (studying sick and well) in terms of:
Person: age, sex, marital status, health conditions, exposure history, or other characteristics.
Place: geography, worksite, occupation, migration status…etc
Time : seasonal variation, epidemics….etc
Studying group of general population rather than a dealing with group of highly-selected individuals studied in a clinic or laboratory as in clinical sciences.

7. Sources of data for epidemiologic studies include:
1- Population data:
.Vital statistics (birth rates, death rates, pregnancy rates, abortion rates, low birth weight).
.Demographic, economic, housing, geographical, and other data from the Census and other government data-gathering activities.
.Summaries of disease and injury reporting systems and registries.
.Workplace monitoring systems.
.Environmental monitoring systems (e.g., air pollution measurements).
.Production and sales data.

8. Sources of data for epidemiologic studies include:
2-Individual-level data
.Vital events registration (births, deaths, marriages).
.Disease and injury reporting systems and registries.
.National surveys.
.Computer data files (e.g., health insurers).
.Medical records.
.Questionnaires - in person, by telephone, mailed.
.Biological specimens (routinely or specially collected).

9. Natural history of disease:
Defining observing, and measuring health and disease requires an appreciation of the concept of natural history – the evolution of a pathophysiologic process.
"Natural" refers to the process in the absence of intervention.
Natural history encompasses the entire sequence of events and developments from the occurrence of the first pathologic change (or even earlier) to the resolution of the disease or death.
The natural history of a disease may be described through a staging classification. Staging can aid in defining uniform study groups for research studies, determining treatment regimens, predicting prognosis, and in providing intermediate end-points for clinical trials.

10. Disease results from complex interaction between man, an
Host
Agent
Environment
Disease results from complex interaction between man, an
agent and the environment.

11. Scheme diagram represents the natural history of disease
Usual time of diagnosis
by symptoms & signs
Prepathogenesis
phase
Pathogenesis phase
Clinical phase
End result of disease in man
Recovery, death or disability
Scheme diagram represents the natural history of disease

12. *Prepathogenesis phase: period before disease. The disease
agent has not yet entered into man. The pathological process did not
start yet. Here the person is exposed to disease by its risk factors.
*Pathogenesis , presymptomatic phase : the pathological process
of disease starts here. If the disease is infectious it begins with the
entry of the disease agent, i.e. m o into the susceptible human body .
* Clinical phase: begins with the development of symptoms and
signs of disease. These periods may vary in time according to type of
the disease e.g. days months even years .

13. development of symptomatic disease". Incubation period may be long or
For infectious diseases, it is important to notice Incubation period
which refers to the "time from infection (entry of the disease agent) to
development of symptomatic disease". Incubation period may be long or
short according to type of disease.
For non-infectious disease Induction "period of time from causal action until
disease initiation".

14. Ice berg phenomenon of AIDS
Ice berg phenomenon : this phenomenon is explained as when the tip of iceberg is seen above the sea while the base of the iceberg which is the biggest portion is below the sea level. e.g. AIDS
(Tip of iceberg)
AIDS cases detected
and diagnosed
1.2million AIDS cases
undetected
8-10 million persons with
HIV infections
Scheme diagram represents
Ice berg phenomenon of AIDS
The more evident picture of disease is usually observed and reported (i.e. cases with symptoms and signs). While sub-clinical or latened cases are not registered unless during screening. e.g. moderate to severe diarrhea cases among infants are admitted to hospitals. While mild and self limited cases treated at home are not admitted. So counting on hospital records will not give us the accurate picture of disease severity.