Topic 2 - The History and Scope of Epidemiology

Question 1

Give 4 details about the 2009 H1N1 influenza case.

Answer 1

April 2009: 2 cases of 2009 H1N1 came
to the attention of CDC.

The initial cases occurred in the U.S. and then
expanded rapidly worldwide.

By summer 2010, the epidemic subsided and
an estimated 60 million cases had occurred in
the U.S.

Heavily affected people were from 18 to 64
years old

Question 2

Give 6 details about the 2006 outbreak of e.coli.

Answer 2

Outbreak during late summer and fall of 2006

Affected 199 persons and caused 3 deaths

Caused 102 (51%) of ill persons to be hospitalized

A total of 31 patients (16%) were afflicted with
hemolytic-uremic syndrome (HUS).

Spread across 26 states

Fresh spinach linked to the outbreak

Question 3

What are 5 typical issues that can arise from epidemiological research studies?

Answer 3

When there is an association between a factor (i.e., contaminants in food and water; animal reservoirs for disease agents) and a health outcome, does this observation mean that the factor is a cause of disease?

If there is an association, how does the occurrence of disease vary according to characteristics of person, place,
and time?

Based on the observation of such an association, what practical steps should public health take? What should the individual consumer do?

Do the findings from an epidemiologic study merit panic or a measured response?

How applicable are the findings to settings other than the one in which the research was conducted? What are the policy implications of the findings?

Question 4

How are epidemiological studies applied?

Answer 4

To the control of health problems in populations

Question 5

What is epidemiology?

Answer 5

The study of the distribution
and determinants of health-related states or
events in specified populations, and the
application of this study to control of health
problems

Question 6

What are the key aspects in the definition of epidemiology?

Answer 6

Determinants

Distribution

Population

Health phenomena

Morbidity and mortality

Question 7

What are determinants? Give examples.

Answer 7

Factors or events that are capable of bringing
about a change in health

Examples:

Biologic agents (bacteria)

Chemical agents (carcinogens)

Less specific factors (stress, drinking,
sedentary lifestyle, or high-fat diet)

Question 8

What is distribution? Give examples.

Answer 8

Frequency of disease occurrence may vary
from one population group to another

The “distribution” refers to person, place, and
time attributes of different diseases in human
populations. This includes identifying the
personal characteristics, locations, and
temporal aspects of how disease occurs

Examples:

In 2006, death rates from CHD and stroke
were higher among African-Americans than
among American Indians/Alaskan natives,
Asian/Pacific Islanders, or whites.

Coronary heart disease occurrence differs
between Hispanics and non-Hispanics

Question 9

Give 3 details about population.

Answer 9

Epidemiology examines disease occurrence
among population groups, not individuals.

Epidemiology is often referred to as
population medicine.

The epidemiologic description indicates
variation by age groups, time, geographic
location, and other variables

Question 10

What is the relationship between epidemiology and clinical practice?

Answer 10

Public health focuses on populations while
clinical practice focuses on individual patients.

Knowledge gained by epidemiology is important for both public health and clinical practice

When a physician examines, advises, and treats a patient, the knowledge used is the result of population-based studies.

Epidemiologic methods and approaches underlie health-based research

Question 11

What kinds of health outcomes does epidemiology investigate?

Answer 11

Infectious diseases

Chronic diseases

Disability, injury, limitation of activity

Mortality

Active life expectancy

Mental illness, suicide, drug addiction

Question 12

What are morbidity and mortality? What are they defined to be used for?

Answer 12

Morbidity: designates illness.

Mortality: refers to deaths that occur in a
population or other group.

Note that most measures of morbidity and
mortality are defined for specific types of
morbidity or causes of death

Question 13

What are the 4 aims of epidemiology?

Answer 13

To describe the health status of populations

To explain the etiology of disease

To predict the occurrence of disease

To control the distribution of disease

Question 14

What is step 1 of the epidemiological approach? What is the basic question that associated with it?

Answer 14

Step 1 – Determine whether there is actually an association present between some exposure (e.g., smoking) and the development of some disease (e.g., cancer).

Accomplished by examining groups with different exposures levels for differences in disease levels

It is important to be sure that the data being used have been gathered accurately and are valid

Basic question: Is there a real difference in disease outcome based on a difference in exposure?

Question 15

What is step 2 of the epidemiological approach? What is the basic question that associated with it?

Answer 15

Step 2 – Determine whether the association is
causal

Even if a real association or difference exists, the association may not be causal

In other words, the exposure of interest may not cause the disease of interest

Many of the methods of epidemiology are concerned with determining whether an association is causal

Basic question: What has caused the association between exposure and disease outcome?

Question 16

According to the epidemiological approach, what characteristics of the person and disease must be described?

Answer 16

Who (Person)

Where (Place)

When (Time)

What (Case Definition)

Why (Causes)

Question 17

Give 3 details about the “who.”

Answer 17

The “person” aspect of disease can include
many variables. These describe the
characteristics of those who get the disease

Age, sex, and race are almost always included

Other person variables that might be included
are social class, occupation, marital status,
health characteristics

Question 18

What is the “where”? Give examples.

Answer 18

Place considers geographic elements:

Political subdivisions (country, state, county, city)

International comparisons

Natural boundaries (mountains, rivers)

Environmental factors (water supply, exposure to pollution)

Urban versus rural locations

Question 19

What is the “when”? What are the 2 kinds?

Answer 19

Time is usually expressed according to month
or year

Secular trends: This refers to changes that occur over a long period of time, such as years or decades.

Cyclic changes: This refers to recurrent cycles in the frequency of disease, often on a yearly or seasonal basis

Question 20

What are 4 details about the “what”?

Answer 20

Case definitions are the standard criteria used to define cases

Case definitions are important so that
comparisons can be made and causes
determined

Case definitions involve specific clinical criteria: symptoms, signs, & laboratory findings

Cases can be classified into categories: Suspected, probable, confirmed

Question 21

Give an example of how changes in case definition can change the number of reported cases.

Answer 21

In 1993, the case definition for AIDS was changed. The definition was expanded to include everyone who had an HIV infection and a CD4 T-cell count below 200/uL. Prior to this, a person with an HIV infection had to have clinical symptoms to be diagnosed as having AIDS.

This resulted in there being a marked increase in the number of cases of AIDS reported. This did not reflect a real increase in AIDS

Question 22

What are the 4 foundations of epidemiology?

Answer 22

Interdisciplinary

Methods and procedures—quantification

Use of special vocabulary

Epidemic frequency of disease

Question 23

How is epidemiology interdisciplinary?

Answer 23

Draws from biostatistics and the social and behavioral sciences, as well as from the medically related fields of toxicology, pathology, virology, genetics, microbiology, and clinical medicine

Question 24

What are 3 details about quantification?

Answer 24

Quantification is a central activity of
epidemiology

Epidemiologic measures often require
counting the number of cases of disease.

Disease distributions are examined according
to demographic variables such as age, sex,
race, and other variables, such as exposure
category and clinical features

Question 25

What is an epidemic?

Answer 25

The occurrence in a community or region of
cases of an illness (or an outbreak) clearly in
excess of normal expectancy…

Relative to usual frequency of the disease

Question 26

What are the key terms in epidemic?

Answer 26

Communicable disease: an illness caused by an infectious agent that can be transmitted from one person to another

Infectious disease: a synonym for a communicable disease

Outbreak: a localized disease epidemic, e.g., in a town or health care facility

Question 27

What is a pandemic? What does “endemic” mean?

Answer 27

An epidemic on a worldwide scale; during a pandemic, large numbers of persons may be affected and a disease may cross international borders.”

Example: flu pandemic

Endemic: to characterize a disease that is habitually present in a particular geographical region

Question 28

What are 2 concepts related to epidemics?

Answer 28

Surveillance and epidemic threshold

Question 29

What are 4 details about surveillance?

Answer 29

The systematic collection of data pertaining to
the occurrence of specific diseases

Analysis and interpretation of these data

Dissemination of disease-related information

Common activities include monitoring food
born disease outbreaks and tracking influenza

Question 30

What are 2 details about epidemic threshold?

Answer 30

The minimum number of cases (or deaths) that would support the conclusion that an epidemic was underway

This is based on statistical projections

Question 31

Who are the key figures of epidemiology history and what are they known for?

Answer 31

John Graunt: summarized the pattern of mortality in 17th century London

William Farr: compiled data on births, deaths etc. as ratios in the 19th century

John Snow: showed that cholera was transmitted by fecal contamination of drinking water in the 19th century

Question 32

How did Hippocrates affect epidemiology?

Answer 32

Hippocrates wrote On Airs, Waters, and Places
in 400 BC

He suggested that disease might be associated with the physical environment

This represented a movement away from supernatural explanations of disease causation

Question 33

Name 5 details about John Graunt.

Answer 33

London tradesman (1620 – 1674)

Founded the Royal Society of London

Laws of mortality (17th century): disease and death is not random; a pattern may exist

First epidemiologist, analyzed weekly
counts of deaths in London

Created the Bills of Mortality

Question 34

How is John Graunt related to the use of mortality counts?

Answer 34

1662: published Natural and
Political Observations Made upon the Bills of
Mortality.

He is credited with being first to use statistics
for understanding disease

Question 35

What were John Graunt’s contributions to epidemiology?

Answer 35

Recorded seasonal variations in births and
deaths

Showed excess male over female differences
in mortality

Known as the “Columbus” of biostatistics

Question 36

Give 7 details about Edward Jenner.

Answer 36

Jenner conducted an experiment to create a
smallpox vaccine

He developed a method for smallpox
vaccination

In 1978 smallpox was finally eliminated
worldwide

Since 1972, routine vaccination of the
nonmilitary population of the U.S. has been
discontinued

In the eighteenth century, smallpox was a widespread major killer. The majority of smallpox victims were infants and young children

It had been observed that milkmaids who developed cowpox, a disease similar to but less severe than smallpox, did not get smallpox

Jenner, an English physician, experimented with inoculating healthy people with material from cowpox lesions. Those who developed cowpox were immune to smallpox. His work led to the discovery of an effective smallpox vaccine in the 1790s

Question 37

Who used natural experiments? What were they for?

Answer 37

John Snow was an English physician and
anesthesiologist

He investigated a cholera outbreak that
occurred during the mid-19th century in
Broad Street, Golden Square, London

Question 38

What is a natural experiment?

Answer 38

Naturally occurring circumstances in
which subsets of the population have different levels of exposure to a supposed causal factor in a situation resembling an actual experiment, where human subjects would be randomly allocated to groups. The presence of persons in a particular group is typically nonrandom

Question 39

What is the story of John Snow and cholera?

Answer 39

John Snow, London physician & student of William Farr, achieved prominence as an
obstetrician who was also a pioneer in use of anesthesia.

His work in epidemiology, however, is his greatest legacy. He is sometimes called
the “father of epidemiology”

Snow conducted careful investigations of cholera epidemics in London during
the mid-1800’s.

Cholera is a bacterial infection that causes severe diarrhea & dehydration. Severe untreated cases can have a mortality of over
50%. With current treatment methods, mortality is less than 1%

Snow believed that cholera was transmitted through the water, not a generally accepted belief. Most believed the miasma theory (including Farr, as mentioned above), which proposed spread through the air.

In 1854, during a major cholera outbreak in London, he made a map showing the locations of public water pumps as well as the locations of cholera deaths.

Snow noted that most deaths were occurring in the areas served by the Broad Street Pump. Although not conclusive, there is some evidence that Snow removed the Broad Street Pump handle, causing the cholera epidemic to cease

Snow’s study of two different water companies that provided water to London provided excellent evidence that cholera was transmitted by water

The Lambeth got water from above where London sewage emptied into the Thames while the Southwark & Vauxhall obtained water from below where sewage entered. Cholera death rates were much greater for
Southwark & Vauxhall (sewage-contaminated water) than for Lambeth districts.

In districts provided water by both companies, Snow determined which company provided the water for a house & the number of cholera deaths in that house

Question 40

What were Snow’s contributions to epidemiology?

Answer 40

Linked the cholera epidemic to contaminated
water supplies

Used a spot map of cases and tabulation of
fatal attacks and deaths

Question 41

What were the results from Snow’s natural experiment?

Answer 41

Two different water companies supplied water from the Thames River to houses in the same area

The Lambeth Company moved its source of
water to a less polluted portion of the river

Snow noted that during the next cholera
outbreak those served by the Lambeth Company had fewer cases of cholera

Question 42

How did Ignaz Semmelweis impact epidemiology?

Answer 42

Mid-19th century, Viennese hospital

Clinical assistant in obstetrics and gynecology

Observed higher mortality rate among the women on the teaching wards for medical students and physicians than on the teaching wards for midwives

Postulated that medical students and physicians had contaminated their hands during autopsies

Introduced the practice of hand washing

Question 43

How did William Farr affect epidemiology?

Answer 43

British Epidemiologist (1837-1841)

Founder of modern epidemiology

Compiled annual counts of births, deaths etc. (vital records)

Compiled data as ratios; counts (numerator) and census data (denominator)

Appointed compiler of abstracts in England,
1839

Provided foundation for classification of
diseases (ICD system)

Used data such as census reports to study
occupational mortality in England

Examined linkage between mortality rates and population density

Beginning in the mid-1800s, Farr built on the
work of Graunt by systematically collecting and analyzing Britain’s mortality statistics. This
established the field of vital statistics

Farr is considered the father of modern vital
statistics (birth & death records) and surveillance

Promoted the idea that some diseases (especially chronic) may have a multifactorial etiology

Question 44

How do Koch affect epidemiology? What are his postulates?

Answer 44

Koch & Louis Pasteur established
the germ theory of disease.

Koch took the first pictures of
microbes and demonstrated that
microorganisms do exist and
cause diseases

Koch showed that anthrax was
transmissible and reproducible
in experimental animals (mice)
and that the anthrax bacillus was
the only organism that caused
anthrax in a susceptible animal

Microorganism must be observed in every
case of the disease

Microorganism must be isolated and grown in
pure culture

Pure culture must, when inoculated into a
susceptible animal, reproduce the disease

Microorganism must be observed in, and
recovered from, diseased animal

Question 45

What are 4 other historical developments in epidemiology?

Answer 45

Alexander Fleming discovered the antimicrobial properties of mold: led to the discovery of the antibiotic penicillin

Alexander Langmuir established CDC’s Epidemic Intelligence Service; Father of infectious disease epidemiology

Wade Hampton Frost was the first professor of epidemiology in the U.S.

Joseph Goldberger discovered the cure for
pellagra

Question 46

What are 7 recent applications of epidemiology?

Answer 46

The Framingham Heart Study (ongoing since
1948) investigates coronary heart disease risk
factors

Smoking and lung cancer; e.g., Doll and Peto’s
study of British doctors’ smoking

AIDS, chemical spills, breast cancer screening,
second-hand cigarette smoke

Infectious diseases: SARS, pandemic influenza 2009 H1N1, Avian influenza

Environmental health

Chronic diseases, lifestyle and health
promotion

Psychological and social epidemiology