MEDICINE AND PHARMACY FACULTY
UNIVERSITY OF ORADEA
EPIDEMIOLOGY
By
CONSTANTA TURDA, M.D.
History
of
Epidemiology
Hippocrates (460-377 B.C.)
On Airs, Waters, and Places
 Idea that disease might
be associated with
physical environment
Thomas Sydenham (1624-1689)
Recognized as a founder
of clinical medicine and
epidemiology
Emphasized detailed
observations of patients
& accurate recordkeeping
James Lind (1700’s)
 Designed first experiments
to use a concurrently
treated control group
Edward Jenner (1749-1823)
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Pioneered clinical trials for vaccination
to control spread of smallpox
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Jenner's work influenced many others,
including Louis Pasteur who developed
vaccines against rabies and other
infectious diseases
Ignas Semmelweis (1840’s)
 Pioneered handwashing
to help prevent the spread
of septic infections in
mothers following birth
John Snow (1813-1858)
 Father of epidemiology
 Careful mapping of cholera
cases in East London during
cholera epidemic of 1854
 Traced source to a single well
on Broad Street that had been
contaminated by sewage
History of Epidemiology (Cont’d)
• Vital Statistics
 John Graunt (1620-1674)
 William Farr (1807-1883)
• Occupational medicine
& Industrial Hygiene
 Bernardino Ramazzini (1633-1714)
• Role of carriers in transmission
 Typhoid Mary & George Soper
Typhoid Mary & George Soper
 Mary Mallon, a cook responsible for most famous outbreaks of
carrier-borne disease in medical history
 Recognized as carrier during 1904 N.Y. typhoid fever epidemic
 When source of disease was traced, Mary had disappeared
only to resurface in 1907 when more cases occurred
 Again Mary fled, but authorities led by George Soper, caught
her and had her quarantined on an island
 In 1910 the health department released her on condition that
she never accept employment involving the handling of food
 Four years later, Soper began looking for Mary again when two
new epidemics broke out; Mary had worked as a cook at both
places
 She was found and returned to North Brother Island, where she
remained the rest of her life until a paralytic stroke in 1932 led
to her slow death, six years later
Typhoid Mary
U.S. History of Epidemiology
• Lemuel Shattuck (1850)
 Proposed creation of a permanent statewide public
health infrastructure
 Recommended establishing state & local health
offices to gather statistical information on public
health conditions
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Quarantine Commissions (1857)
1st Public Health Book (1879)
U.S. Public Health Service founded (1902)
Pure Food and Drug Act (1906)
Pasteurization of milk (1913)
1st School of Public Health (1913)
Historic Aspects of the
Development of Morbidity
Statistics in the U.S.
• Edgar Sydenstricker (Early 1900’s)
 Pioneer public health statistician
• Three notable studies:
Tuskegee syphilis study (1932-1970)
Framingham heart study (1948-present)
Epidemiology of cigarette smoking
(1950’s - present)
Modern History of
Epidemiology in the U.S.
• Mortality stats in first half of century
Unstable because of outbreaks of
infection
• Stats reversed by 1950’s because of
childhood immunizations, medical
interventions and public health
measures
• Economic growth reduced squalor
• Introduction of antibiotics in 50’s
Wake-up Calls
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Over-optimism in 60’s and 70’s
AIDS recognized
Cholera in the southern hemisphere
Legionnaire’s disease
New forms of hepatitis
Chlamydia and heart disease
Hospital acquired infections
Antibiotic resistance
U.S.Mortality Index
(annual deaths/100,000)
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1900 - 500
1918-1919- 850
Mid-century-1982 - 30
1982-1994 - 60
Future Challenges
• Instant global transmission of
pathogens
Population overcrowding
Ease of travel
Importation of foods
DEFINITIONS
• What is epidemiology?
• What is an epidemiologist?
EPIDEMIOLOGY is the study
of the nature, cause, control
and determinants of the
frequency and distribution of
disease, disability, and death
in human populations.
Epidemiology: the study of factors influencing the
occurence, transmission, distribution, prevention
and control of disease in a defined population
An EPIDEMIOLOGIST is a
public health scientist, who is
responsible for carrying out all
useful and effective activities
needed for successful
epidemiology practice
Methods of Epidemiology
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Public Health Surveillance
Disease Investigation
Analytic Studies
Program Evaluation
Terminology
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Endemic
Hyperendemic
Holoendemic
Epidemic
Pandemic
Epizootic
Incidence
Prevalence
Terms used for reference
to various forms of
outbreaks
Endemic: a disease or pathogen present or usually prevalent
in a given population or geographic region at all times
Hyperendemic: equally endemic in all age groups of a
population
Holoendemic: endemic in most of the children in a
population, with the adults in the same population being less
often affected
Epidemic: a disease occuring suddenly in numbers far
exceeding those attributable to endemic disease; occuring
suddenly in numbers clearly in access of normal expectancy
Pandemic: a widespread epidemic distributed or occuring
widely throughout a region, country, continent, or globally
Epizootic: of, or related to a rapidly spreading and widely
diffused disease affecting large numbers of animals in a
given region
Incidence: rate of occurrence of an event; number of new
cases of disease occuring over a specified period of time;
may be expressed per a known population size
Prevalence: number of cases of disease occurring within a
population at any one given point in time
Terms Associated with
Disease Causation, etc.
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Host
Agent
Environment
Fomites
Vector
Carrier – active
Incubatory
Convalescent
Healthy
Intermittent
Your Assignment:
Define these terms
Changing Patterns of
Community Health
• Health patterns in constant state of flux
• Infectious versus chronic diseases
• Population and age-related
Chain of Infection
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Etiological agent
Source/Reservoir
Portal of exit
Mode of transmission
Portal of entry
Susceptible host
Classification of
Microorganisms
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Viruses
•RNA–DNA
• RNA viruses genetically unstable
•Lipid enveloped–nonenveloped
• Solvent-detergent treatments virucidal only for enveloped
viruses
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Bacteria
•Gram-positive–gram-negative•Antibiotic sensitivity differs
• Diagnostic and therapeutic uses of gram-negative
capsule
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Fungi
 •Disseminated vs. superficial
 •Mold vs. biphasic
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Parasites
•Complete cycle
•Larval migrans
A Clinician’s View
• Diseases classified according to
signs and symptoms:
1. Diarrheal diseases
2. Respiratory diseases
3. Cutaneous/soft tissue infection
4. CNS diseases
5. Septicemic diseases
6. Fever of undetermined origin
Modes of Transmission
• Contact transmission
• Vehicle transmission
• Vector transmission
An Epidemiologist’s View
Means of Spread of Infectious Diseases
• Contact
•Direct
• •Indirect•Fomites
• • Body secretions (blood, urine, saliva, etc.)
• Vector
Airborne
• •Small-particle aerosol
Some Infectious Diseases
Spread by Contact
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Salmonellosis
2. Campylobacter
3. Shigellosis
4. Clostridium perfringens food
poisoning
5. Staphylococcal enterotoxin food
poisoning
6. Cholera
7. Giardiasis
8. Listeriosis
Some Important Food- and
Waterborne Infections
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Salmonellosis
2. Campylobacter
3. Shigellosis
4. Clostridium perfringens food
poisoning
5. Staphylococcal enterotoxin food
poisoning
6. Cholera
7. Giardiasis
8. Listeriosis
Some Important Airborne
Infections
• 1. Tuberculosis
• 2. Influenza
• 3. Childhood Infections
 − Measles, mumps, rubella, pertussis
• 4. Parainfluenza
• 5. RSV
• 6. Legionella
Some Important Vectorborne
Infections
• 1. Malaria
• 2. Viral encephalitis
 − SLE, WEE, EE, VE, California virus
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3. Schistosomiasis
4. Tularemia
5. Dengue
6. Yellow fever
7. Rocky Mountain spotted fever
8. Leishmaniasis
9. Trypanosomiasis
Reservoirs of Infectious
Diseases
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1. Human
2. Animal (zoonoses)
3. Soil
4. Water
Some Infectious Diseases
with a Human Reservoir
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1. AIDS (HIV infection)
2. Syphilis
3. Gonorrhea
4. Shigellosis
5. Typhoid fever
6. Hepatitis-B virus
7. Herpes simplex virus
Some Diseases with an
Animal Reservoir (Zoonoses)
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1. Nontyphoidal salmonellosis
2. Brucellosis
3. Anthrax
4. Listeriosis
5. Viral encephalitis (SLE,WEE, CEE)
6. Rabies
7. Plague
Some Important Diseases with
a Soil Reservoir
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1. Histoplasmosis
2. Coccidioidomycosis
3. Blastomycosis
4. Tetanus
5. Botulism
Some Infectious Diseases
with a Water Reservoir
• 1. Pseudomonas infections
− Sepsis, UTI, “hot tub” folliculitis
• 2. Legionnaires’ disease
• 3. Melioidosis
Some Infectious Diseases
Spread by Contact
• Sexually transmitted diseases
 − Syphilis, gonorrhea, chlamydia, AIDS
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2. Staphylococcal infections
3. Streptococcal infections
4. Many nosocomial infections
5. Rhinovirus colds
6. Brucellosis (slaughter house contact)
7. Hepatitis B virus infection
Classes of Epidemics
• Common source (vs. sporadic)
Point source
Intermittent
Continuous
Propagated
Your Assignment:
Define these terms
& identify which apply
to the following
three graphs
Infectious Agents: 3 Important
Epidemiologic Properties
• 1. Infectivity
 − The propensity for transmission
 − Measured by the secondary attack rate in a household,
school, etc.
• 2. Pathogenicity
 − The propensity for an agent to cause disease or clinical
symptoms
 − Measured by the apparent : inapparent infection ratio
• 3. Virulence
 − The propensity for an agent to cause severe disease
 − Measured by the case fatality ratio
Infectious Agents: 3 Important
Epidemiologic Properties
Incubation period = The period between
exposure to the agent and onset of
infection (with symptoms or signs of
infection)
Secondary attack rates = The rates of
infection among exposed susceptibles
after exposure to an index case, such
as in a household or school
Definitions of Some Relevant
Terms (cont.)
 􀂄Inapparent(or subclinical infection)− An infection with no
clinical symptoms, usually diagnosed by serological
(antibody) response or culture
 􀂄Immunity− The capacity of a person when exposed to an
infectious agent to remain free of infection or clinical illness
 􀂄Herd immunity− The immunity of a group or community. The
resistance of a group to invasion and spread of an infectious
agent, based upon the resistance to infection of a high
proportion of individual members of the group. The resistance
is a product of the number of susceptibles and the probability
that those who are susceptible will come into contact with an
infected person.
Definitions of Some Relevant
Terms (cont.)
 􀂄Persistent infection− A chronic infection with
continued low-grade survival and
multiplication of the agent
 􀂄Latent infection− An infection with no active
multiplication of the agent, as when viral
nucleic acid is integrated into the nucleus of a
cell as a provirus. In contrast to a persistent
infection, only the genetic message is present
in the host, not viable organisms.
Disease Investigation
• Establish diagnosis
• Identify specific agent
• Describe according to person, place
and time
• Identify source of agent
• Identify mode of transmission
• Identify susceptible populations
Epidemiology and Clinical
Practice
• Clinical practice dependent on
epidemiology
• Epidemiology defines natural history
of disease
• Even descriptive information is
useful
The Epidemiologic
Approach
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Multistep process
First - determine association
Then prove causation
Not all associations are causal
Examine validity, false assumptionse.g. - fluoride in water
Analytic Studies
• Type of study
• Design
• Analysis of data
Epidemiology and
Prevention
• Identify high risk populations
• Modify risks
• Prevent exposures
Levels of Prevention
• Primary
• Secondary
• Tertiary
Levels of Prevention (cont’d)
• Primary
Involves halting any occurrence of
a disease or disorder before it
happens
Levels of Prevention (cont’d)
• Secondary
Health screening and detection
activities
Levels of Prevention (cont’d)
• Tertiary
Retard or block the progression of
condition