assignment week 1 Managerial Epidemiology

Chapter 1

The History and Scope of Epidemiology

Learning Objectives

• Define the term epidemiology

• Define the components of epidemiology (determinants, distribution, morbidity, and mortality)

• Name and describe characteristics of the epidemiologic approach

• Discuss the importance of Hippocrates’ hypothesis and how it differed from the common beliefs of the time

• Discuss Graunt’s contributions to biostatistics and how they affected modern epidemiology

• Explain what is meant by the term natural experiments, and give at least one example

2009 H1N1 Influenza

• During 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. See Exhibit 1-1.

2006 Outbreak of Escherichia coli

• 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

Epidemiology Defined

• Epidemiology derives from "epidemic," a

term which provides an immediate clue to

its subject matter. Epidemiology originates

from the Greek words, epi (upon) + demos

(people) + logy (study of).

Definition of Epidemiology

• Epidemiology is concerned with the

distribution and determinants of health and

diseases, morbidity, injuries, disability, and

mortality in populations.

• Epidemiologic studies are applied to the

control of health problems in populations.

Key Aspects of This Definition

• Determinants

• Distribution

• Population

• Health phenomena

• Morbidity and mortality

Determinants

• Factors or events that are capable

of bringing about a change in health.

Examples of Determinants

• Biologic agents--bacteria

• Chemical agents--carcinogens

• Less specific factors--stress, drinking,

sedentary lifestyle, or high-fat diet

The Search for Determinants

• Outbreak of Fear--Ebola virus in Kikwit,

Zaire

• Fear on Seventh Ave.--Legionnaires’ disease in New York City

• Red Spots on Airline Flight Attendants--

dye from life vests

• Bioterrorism-Associated Anthrax Cases

Bioterrorism-Associated

Anthrax Cases

• Index case reported in Florida

• Additional cases, including fatal cases,

reported in New York, New Jersey,

Connecticut

• Contaminated mail linked to some of the

cases

Distribution

• Frequency of disease occurrence

may vary from one population group

to another.

Disease Distribution 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.

Population

• 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.

Health Phenomena

• Epidemiology investigates many

different kinds of health outcomes:

– Infectious diseases

– Chronic diseases

– Disability, injury, limitation of activity

– Mortality

– Active life expectancy

– Mental illness, suicide, drug addiction

Morbidity and Mortality

• 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.

Aims and Levels

• To describe the health status of

populations

• To explain the etiology of disease

• To predict the occurrence of disease

• To control the occurrence of disease

Foundations of Epidemiology

• Interdisciplinary

• Methods and procedures—quantification

• Use of special vocabulary

• Epidemic frequency of disease

Epidemiology Is Interdisciplinary

• Epidemiology is an interdisciplinary field

that 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.

Quantification • 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.

Epidemic

• “The occurrence in a community or region of cases of an illness (or an outbreak)

clearly in excess of expectancy…”

• Relative to usual frequency of the disease

Key Terms in “Epidemic”

• 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

Concept of Epidemic and Non-

Infectious Diseases

• Some examples that use the concept of an

epidemic are:

– Love Canal

– Red spots among airline flight attendants

– Toxic Shock Syndrome

– Brown lung disease

– Asbestosis among shipyard workers

– Diseases associated with lifestyle

Pandemic

• “ . . . an epidemic on a worldwide scale; during a pandemic, large numbers of

persons may be affected and a disease

may cross international borders.” An example is a flu pandemic.

Ascertainment of Epidemics

• Surveillance

• Epidemic threshold

Surveillance

• 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.

Epidemic Threshold

• The minimum number of cases (or deaths)

that would support the conclusion than an

epidemic was underway.

• This is based on statistical projections.

• Figure1-6 demonstrates that the combined

pneumonia and influenza deaths peaked

substantially above the epidemic threshold

during early 2008, late 2009, and early

2011.

Historical Antecedents • The Cholera Fountain

• Environment and disease

• The Black Death

• Use of mortality counts

• Smallpox vaccination

• Use of natural experiments

• William Farr

• Identification of specific agents of disease

• The 1918 influenza pandemic

The Cholera Fountain

Dresden, Germany

• Dresden, Germany, was spared from a

deadly cholera epidemic during 19th

Century.

• Mid 1800s--Residents constructed a

Cholera Fountain to express their gratitude

for escaping the cholera epidemic that

threatened the city.

The Environment

• 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.

The Black Death

• Occurred between 1346-1352.

• Claimed one-quarter to one-third of

population of Europe.

Use of Mortality Counts

• John Graunt, in 1662, published Natural

and Political Observations Made upon the

Bills of Mortality.

John Graunt’s Contributions

• Recorded seasonal variations in births and

deaths

• Showed excess male over female

differences in mortality

• Known as the “Columbus” of biostatistics

• See Yearly Mortality Bill for 1632: The 10

Leading Causes of Mortality in Graunt’s

Time.

Edward Jenner

• 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.

Use of Natural Experiments

• 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.

Snow’s Contributions

• Linked the cholera epidemic to

contaminated water supplies

• Used a spot map of cases and tabulation

of fatal attacks and deaths

Snow’s Natural Experiment

• 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.

Natural Experiment

• Refers to “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.”

Ignaz Semmelweis • 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

William Farr

• 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

Koch's Postulates

• 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

The 1918 Influenza Pandemic

• “The Mother of All Pandemics” and

Spanish Flu

• Occurred between 1918 and 1919

• Killed 50- to 100 million persons worldwide

• 2.5% case-fatality rate versus 0.1% for

other influenza pandemics

• Deaths most frequent among 20- to 40-

year-olds

Other Historical Developments

• Alexander Fleming discovered the

antimicrobial properties of the mold: led to

the discovery of the antibiotic penicillin.

• Alexander Langmuir established CDC’s Epidemic Intelligence Service.

• Wade Hampton Frost was the first

professor of epidemiology in the U.S.

• Joseph Goldberger discovered the cure for

pellagra.

Recent Applications of

Epidemiology

• 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

• Association between HPV and cervical

cancer

Additional Applications of

Epidemiology

• Infectious diseases

– SARS, pandemic influenza 2009 H1N1,

Avian influenza

• Environmental health

• Chronic diseases

• Lifestyle and health promotion

• Psychological and social epidemiology

• Molecular and genetic epidemiology