Basic epidemiology_Training for Medics

Basic Epidemiology (Medic CME)
Dr. Arkar, Clinical Consultant, Mae Tao Clinic

MCQ - 1
“Epidemiologic Triangle” is included
A. agent, host and environment
B. Social determinant of health
C. Modern era model
D. All of the above is WRONG

MCQ - 2
Observational Cross-sectional Study is
A. To assess the presence (prevalence) of the health outcome
B. Study at that point of time without regard to duration.
C. Used routinely to document the prevalence
D. All of the above is TRUE

MCQ - 3
Descriptive epidemiology includes
A. 5 W: What, Who, Where, When, Why
B. 3 S: Symptoms, signs and Season
C. 3 Factors: Agent, Host and Environment
D. All of the above is TRUE.

OUTBREAK: THE WORST
PANDEMICS IN HISTORY

Death Toll: 36 million
Cause: HIV/AIDS
First identified in Democratic Republic of
the Congo in 1976, HIV/AIDS has truly
proven itself as a global pandemic, killing
more than 36 million people since 1981.
Between 2005 and 2012 the annual
global deaths from HIV/AIDS dropped
from 2.2 million to 1.6 million.
HIV/AIDS PANDEMIC
(AT ITS PEAK, 2005-2012)

Cause: Influenza
A category 2 Flu pandemic sometimes
referred to as “the Hong Kong Flu,” the
1968 flu pandemic was caused by the
H3N2 strain of the Influenza A virus, a
genetic offshoot of the H2N2 subtype.
From the first reported case on July 13,
1968 in Hong Kong, it took only 17 days
before outbreaks of the virus were
reported in Singapore and Vietnam, and
within three months had spread to The
Philippines, India, Australia, Europe, and
the United States.
FLU PANDEMIC (1968)

ASIAN FLU
(1956-1958)
Cause: Influenza
Asian Flu was a pandemic outbreak of Influenza A of the H2N2 subtype,
that originated in China in 1956 and lasted until 1958. In its two-year
spree, Asian Flu traveled from the Chinese province of Guizhou to
Singapore, Hong Kong, and the United States. Estimates for the death toll
of the Asian Flu vary depending on the source, but the World Health
Organization places the final tally at approximately 2 million deaths,
69,800 of those in the US alone.

FLU PANDEMIC
(1918)
Death Toll: 20 -50 million
Cause: Influenza
Between 1918 and 1920 a disturbingly deadly outbreak of influenza
tore across the globe, infecting over a third of the world’s
population and ending the lives of 20 – 50 million people. Of the
500 million people infected in the 1918 pandemic, the mortality rate
was estimated at 10% to 20%, with up to 25 million deaths in the
first 25 weeks alone.

THIRD
CHOLERA
PANDEMIC
(1852–1860)
Cause: Cholera
Generally considered the most deadly of the seven cholera
pandemics, the third major outbreak of Cholera in the 19th century
lasted from 1852 to 1860. Like the first and second pandemics, the
Third Cholera Pandemic originated in India, spreading from the
Ganges River Delta before tearing through Asia, Europe, North
America and Africa and ending the lives of over a million people.

THE BLACK
DEATH
(1346-1353)
Death Toll: 75 – 200 million
Cause: Bubonic Plague
From 1346 to 1353 an outbreak of the Plague
ravaged Europe, Africa, and Asia, with an estimated
death toll between 75 and 200 million people.

PLAGUE OF
JUSTINIAN
(541-542)
Cause: Bubonic Plague
Thought to have killed perhaps half the population of
Europe, the Plague of Justinian was an outbreak of the
bubonic plague that afflicted the Byzantine Empire and
Mediterranean port cities, killing up to 25 million people in
its year long reign of terror.

Epidemiologic
Triangle
The epidemiologic triangle is made
up of three parts: agent, host and
environment
(Traditional model for infectious disease)

History of Epidemiology
Although epidemiology as a discipline has
blossomed since World War II,
epidemiologic thinking has been traced
from Hippocrates.
Hippocrates attempted to explain disease
occurrence from a rational rather than a
supernatural viewpoint. In his essay
entitled “On Airs, Waters, and Places,”
Hippocrates suggested that environmental
and host factors such as behaviors might
influence the development of disease.
BC 460

Fathers of epidemiology
Year
1662 John Graunt, a London
haberdasher and councilman
published a landmark analysis of
mortality data in 1662.
1800 an anesthesiologist named John
Snow
conducting a series of
investigations in London that
warrant his being considered the
“father of field epidemiology.”
Twenty years before the
development of the microscope,
Snow conducted studies of cholera
outbreaks both to discover the
cause of disease and to prevent its
recurrence.

Spot map of deaths from cholera
in Golden Square area, London, 1854 (redrawn from original)
his now famous studies in 1854 when an
epidemic of cholera erupted in the Golden
Square of London.
He began his investigation by determining
where in this area persons with cholera
lived and worked.
He marked each residence on a map of the
area, as shown in Figure.
Today, this type of map, showing the
geographic distribution of cases, is called a
spot map.

Definition of
Epidemiology
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

Study:
collection, analysis and interpretation
Distribution:
Frequency (number of health events)
and Pattern (by time, place, person)
Determinants:
Why? How?
Health-related states:
Disease
Specified population:
Community
Application:
Community based practice.
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

The Epidemiologic Approach
As with all scientific endeavors, the practice of epidemiology relies on a systematic approach. In very simple terms,
the epidemiologist:
Counts cases or health events, and describes them in terms of time, place, and person;
Divides the number of cases by an appropriate denominator to calculate rates; and
Compares these rates over time or for different groups of people.

Descriptive epidemiology
The 5W's of descriptive epidemiology:
What = health issue of concern
Who = person
Where = place
When = time
Why/how = causes, risk factors, modes of transmission

Analytic Epidemiology
Key feature of analytic epidemiology = Comparison group
Two categories: experimental and observational.
- Clinical Trial
- Community Trial
- Cohort study
- Case control study
- Cross-sectional study

Observational Cohort Study
- similar in concept to the experimental study.
- The epidemiologist records whether each study participant is exposed or not, and then
- Tracks the participants to see if they develop the disease of interest.
- After a period of time, the investigator compares the disease rate in the exposed group with the disease rate in the
unexposed group.
- In RH IPD, there are 22 medics. In Medical IPD, there are 22 medics.
- They all are enrolled in “Cohort study of physical change”, 2 year study.
- Exposure is Dr. Menno who works in RH IPD since February 2017.
In February 2019,
- 15 medics from RH IPD become look like “Long neck Karen”
- 2 medics from Medical IPD become same symptom.
To be more
understanding.

Relative risk
Disease
Exposure Yes No Total
Yes A B A+B
No C D C+D
Total A+C B+D
Exposure to Dr. Menno has Long neck Karen symptoms.
In epidemiology, it is called “ the exposure is said to be
associated with illness”
Relative risk is 7.6.
“Working inside RH IPD has 7.6 times more risk to get “Long
neck symptom” compared with Medical IPD.
Long neck symptom
Working
with Dr.
Menno
Yes No Total
Yes (RH) 15 (a) 7 (b) 22
No (Med) 2 (c) 20 (d) 22
Total 17 27 44
RR = [a/(a+b)] / [c/(c+d)]
= [15/22] / [2/22]
= 0.68 / 0.09
= 7.6

Observational Case-Control Study
- Enrolling a group of people with disease (cases)
- As a comparison group, enrolls a group of people without disease (controls).
- Then compare previous exposures between the two groups.
- The control group provides amount of exposure as well as in case group.
- If the amount of exposure among the case group is substantially higher than the amount you would
expect based on the control group, then illness is said to be associated with that exposure.

Observational Cross-sectional Study
- a sample of persons from a population is enrolled
- their exposures and health outcomes are measured simultaneously.
- The cross-sectional study tends to assess the presence (prevalence) of the health outcome at that point of
time without regard to duration.
- For example, in a cross-sectional study of diabetes, some of the enrollees with diabetes may have lived with their
diabetes for many years, while others may have been recently diagnosed.
- Cross-sectional studies are used routinely to document the prevalence in a community of health behaviors
(prevalence of smoking), health states (prevalence of vaccination against measles), and health outcomes,
particularly chronic conditions (hypertension, diabetes).

Summary
- Purpose of an analytic study in epidemiology is to identify and quantify the relationship between an exposure and a
health outcome.
- The hallmark of such a study is the presence of at least two groups
- In an observational cohort study, subjects are enrolled or grouped on the basis of their exposure, then are followed to
document occurrence of disease. Differences in disease rates between the exposed and unexposed groups lead
investigators to conclude that exposure is associated with disease.
- In an observational case-control study, subjects are enrolled according to whether they have the disease or not, then
are questioned or tested to determine their prior exposure. Differences in exposure prevalence between the case and
control groups allow investigators to conclude that the exposure is associated with the disease.
- Cross-sectional studies measure exposure and disease status at the same time, and are better suited to descriptive
epidemiology than causation.

GROUP WORK
Group 1: Malaria
Group 2: TB
Group 3: HIV/AIDS

Thank you!
For the community
With the community
In the community
Dr. Arkar Linn Naing

Basic epidemiology_Training for Medics

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