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Epidemiology and
Public Health
EPIDEMIOLOGY │ INTERACTIONS AMONG PATHOGENS, HOSTS, AND
ENVIRONMENTS │ │
CHAIN OF INFECTION STRATEGIES FOR BREAKING THE CHAIN
│
OF INFECTION RESERVOIRS OF INFECTION │ MODES OF TRANSMISSION│
PUBLIC HEALTH AGENCIES │ BIOTERRORISM AND BIOLOGICAL WARFARE AGENTS
│ WATER SUPPLIES AND SEWAGE DISPOSAL

GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA

│
PREPARED BY ANYAYAHAN, OREBILLO & SILVA
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Introduction
Both pathology and
epidemiology can be loosely
defined as the study of disease,
but they involve different
aspects of disease.
PATHOLOGIST - studies the
structural and functional
manifestations of disease and
is involved in diagnosing
diseases in individuals
 EPIDEMIOLOGIST - studies the 3
factors that determine the
frequency, distribution, and
determinants of diseases in
human populations

EPIDEMIOLOGY - study of
factors that determine the
frequency, distribution, and
determinants of diseases in
human populations, and ways to
prevent, control, or eradicate
diseases in populations.
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Epidemiologists are concerned
with:
WHO becomes infected?
WHAT pathogens are causing the infections?
WHERE do the pathogens come from?
WHEN do certain diseases occur?
WHY do some diseases occur in certain places but
not in others?
HOW are pathogens transmitted?
Do some diseases occur only at certain times of the
year? If so, why?
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Spotlighting
Epidemiologists
EPIDEMIOLOGISTS - scientists who
specialize in the study of disease
and injury patterns (incidence and
distribution patterns) in
populations, and ways to prevent
or control diseases and injuries
they study virtually all types of
diseases, including heart,
hereditary, communicable, and
zoonotic diseases and cancer
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Duty of
Epidemiologists
Data collection
Statistical analysis of data

EPIDEMIOLOGISTS - disease
detectives, gathering and piecing
together clues to determine:
What causes a particular
disease,
Why it occurs only at certain
times, and;
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CONT.
Why certain people in a population get the
disease while others do not.

Educational Background
Doctor of Philosophy degree (PhD or DPhil)
Master of Science or Master of Public Health
degree (MS or MPH)
Bachelor of Science degree (e.g., RN degree)
Specialized training in epidemiology
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EPIDEMIOLOGIC
TERMINOLOGY
COMMON TERMS ADJECTIVES (to describe
communicable the status of a particular
contagious infectious disease in a
zoonotic diseases given population)
incidence sporadic
morbidity rate endemic
prevalence epidemic
mortality rate of a pandemic
particular disease
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Communicable
and Contagious
Diseases
GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA
INFECTIOUS DISEASE - 10
(infection) is a disease that is
caused by a pathogen

COMMUNICABLE DISEASE - if
the infectious disease is
transmissible from one human to
another (i.e., person to person)

CONTAGIOUS DISEASE - a
communicable disease that is
easily transmitted from one
person to another
EXAMPLES OF 11
CONTAGIOUS
DISEASES
Hepatitis A.
Hepatitis B.
Hepatitis C.
Novel Coronavirus (COVID-
19)
Influenza (Flu)
Measles.
Meningococcal Disease.
ZOONOTIC DISEASES/ZOONOSES - 12
infectious diseases that humans
acquire from animal sources

INCIDENCE RATE - number of new

cases of that disease in a defined
population during a specific time
period

MORBIDITY RATE - number of new

cases of a particular disease that
occurred during a specified time
period per a specifically defined
population (usually per 1,000,
10,000, or 100,000 population)
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INFECTIOUS COMMUNICABLE CONTAGIOUS

DISEASE DISEASE DISEASES

infectious
communicable
diseases that
can be
diseases that
diseases are easily
transmitted
caused by transmitted
from one human
pathogens to another (i.e., from one
person to person to
person) another
PREVALENCE 14
TWO TYPES:
period prevalence : of a particular disease
is the number of cases of the disease
existing in a given population during a
specific time period
point prevalence : of a particular disease
is the number of cases of the disease
existing in a given population at a
particular moment in time
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MORTALITY RATE
also known as death rate
ratio of the number of people who
died of a particular disease during a
specified time period per a
specified population (usually per
1,000, 10,000, or 100,000
population)
SPORADIC DISEASES 16
a disease that occurs only occasionally (sporadically)
within the population of a particular geographic area

ENDEMIC DISEASES
diseases that are always present within the population
of a particular geographic area

EPIDEMIC DISEASES
a greater than usual number of cases of a disease in a
particular region, usually occurring within a relatively
short period of time
List of Epidemics that have occurred 17
in the United States within the past
35 years:
1976. An epidemic of a respiratory disease (Legionnaires’
disease or legionellosis) occurred during an American
Legion convention in Philadelphia, Pennsylvania.
1992–1993. An epidemic involving Escherichia coli
O157:H7-contaminated hamburger meat occurred in the
Pacific northwest.
1993. An epidemic of hantavirus pulmonary syndrome
(HPS) occurred on Native American reservations in the
Four Corners region (where the borders of Colorado, New
Mexico, Arizona, and Utah all meet).
CONT. 18
1993. An epidemic of cryptosporidiosis (a diarrheal
disease) occurred in Milwaukee, Wisconsin. It
resulted from drinking water that was
contaminated with the oocysts of Cryptosporidium
parvum (a protozoan parasite).
2002. An epidemic of West Nile virus (WNV)
infections occurred throughout the United States.
More than 4,100 human cases occurred that year,
resulting in 284 deaths.
Waterborne disease outbreaks.
Foodborne disease outbreaks.
PANDEMIC 19
DISEASES
a disease that is occurring
in epidemic proportions in
many countries
simultaneously— sometimes
worldwide
Collectively, HIV/AIDS, TB,
and malaria cause more
than 300 million illnesses
and more than 5 million
deaths per year.
THE BROAD 20
STREET PUMP
Mid-19th century
John Snow
Epidemiologic investigation of
a cholera outbreak in London
He ordered the removal of the
handle of the Broad Street
water pump, thus helping to
end an epidemic that had
killed more than 500 people
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JOHN SNOW

“Father of
Epidemiology”
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HIV/AIDS

Common
Modes of HIV
transmission
AIDS in the 23
United States
AIDS epidemic
officially began with publication of the June 5,
1981
issue of Morbidity and Mortality Weekly Report
issue contained a report of five cases of
Pneumocystis carinii pneumonia (PCP) in male
patients at the UCLA Medical Center
Human Immunodeficiency Virus (HIV) - was
discovered in 1983
TUBERCULOSIS 24
many strains of Mycobacterium
tuberculosis (the bacterium
that causes TB) have
developed resistance to the
drugs that are used to treat TB
TB caused by these strains is
known as multidrug-resistant
tuberculosis (MDR-TB), or in
some cases, extensively drug-
resistant tuberculosis (XDR-TB)
Someone in the world becomes
newly infected with M.
tuberculosis every second.
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MALARIA
world’s most important
tropical parasitic disease,
killing more people than
any other communicable
disease, except TB
Africa has the largest
number of people living in
areas with a high risk of
malaria, followed by the
Southeast Asia region.
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Interactions Among
Pathogens, Hosts,
and Environment
GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA
1. Factors pertaining to the pathogen:
The virulence of the pathogen
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A way for the pathogen to enter the body
The number of organisms that enter the body
2. Factors pertaining to the host (i.e., the person who may
become infected):
The person’s health status
The person’s nutritional status
Other factors pertaining to the susceptibility of the host
3. Factors pertaining to the environment:
Physical factors
Availability of appropriate reservoirs
Sanitary and housing conditions
Availability of potable (drinkable) water
CHAIN OF 28
INFECTION
SIX COMPONENTS:
A pathogen
A reservoir of
infection
A portal of exit
A mode of
transmission
A portal of entry
A susceptible host
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STRATEGIES FOR BREAKING
THE CHAIN OF INFECTION
BROAD GOALS:
Eliminate or contain the reservoirs of pathogens or
curtail the persistence of a pathogen at the source
Prevent contact with infectious substances from
exit pathways
Eliminate means of transmission
Block exposure to entry pathways
Reduce or eliminate the susceptibility of potential
hosts
METHODS 31

Use PPE whenever

Proper hand hygiene Adequate rest appropriate

Dispose of
Obtain Insect control Proper isolation infectious wastes
immunization measures procedures properly
GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA 32

Reservoirs of
Infection
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RESERVOIRS
sources of microbes that
cause infectious diseases
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LIVING RESERVOIRS

Living reservoirs include

humans, household pets, farm
animals, wild animals, certain
insects, and certain arach
nids (ticks and mites).
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Human Carriers

The most important reservoirs of human

infectious diseases are other humans—
people with infectious diseases as well as
carriers.
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CARRIER
Passive carriers
Incubatory carrier
Convalescent carriers
Active carriers
 Animals 37
Infectious diseases that humans
HISTORICAL acquire from animal sources are
called zoonotic diseases or zoonoses.
NOTE Many pets and other animals are
important reservoirs of zoonoses.
“Typhoid
Arthropods
Mary”: An As a group, they are so commonly
Infamous associated with human infections.
Many different types of arthropods serve
Carrier as reservoirs of infection, including
insects (e.g., mosqui- toes, biting flies,
lice, fleas), and arachnids (e.g., mites,
ticks).
Transmission of Bacteria that 38
Cause Lyme Disease
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Examples of
Zoonotic Diseases
GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA
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Dogs, cats, bats, skunks, and other
animals are known reservoirs of rabies.
The rabies virus is usually transmitted to
a human through the saliva that is
injected when one of these rabid animals
bites the human.
The most prevalent zoonotic infection in
the United States is Lyme disease, one of
many arthropod-borne zoonoses.
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Nonliving Reservoirs
Nonliving or inanimate
reservoirs of infection include
air, soil, dust, food, milk,
water, and fomites.
Food and milk may be contaminated by careless
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handling, which allows pathogens to enter from soil,
dust particles, dirty hands, hair, and respiratory
secretions.
Human and animal fecal matter from
outhouses, cesspools, and feed lots is often
carried into water supplies. Improper
disposal of sewage and inadequate
treatment of drinking water contribute to
the spread of fecal and soil pathogens.
Fomites are inanimate objects capable of
transmitting pathogens.
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STUDY AID MODES OF TRANSMISSION
Tickborne Hospital staphylococcal epidemic
Diseases of the may begin when aseptic conditions
United States are relaxed and a Staphylococcus
aureus carrier transmits the
Viral diseases
pathogen to susceptible patients
Bacterial diseases (e.g., babies, surgical patients,
Protozoal disease debilitated persons).
Could quickly spread throughout the
entire hospital population.
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FIVE PRINCIPAL MODES
1. CONTACT
2. DROPLET
3. AIRBORNE
4. VEHICULAR
5. VECTOR
TRANSMISSION
Common Routes of Transmission 50
of Infectious Diseases
1. Direct skin-to-skin contact
For example, the common cold virus is frequently
transmitted from the hand of someone who just
blew his or her nose to another person by hand
shaking.
2. Direct mucous membrane-to-mucous
membrane contact by kissing or sexual
intercourse.
Most STDs are transmitted in this manner.
3. Indirect contact via airborne droplets of
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respiratory secretions, usually produced as a
result of sneezing or coughing.
Most contagious airborne diseases are caused by
respiratory pathogens carried to susceptible people
in droplets of respiratory secretions.
4. Indirect contact via food and water contaminated
with fecal material.
5. Indirect contact via arthropod vectors.
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6. Indirect contact via
fomites
7. Indirect contact via
transfusion of
contaminated blood
or blood products
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PUBLIC HEALTH AGENCIES

GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA

Public Health Agencies
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At all levels constantly strive
to prevent epidemics.
One way in which
healthcare personnel
participate in this massive
program is by reporting
cases of communicable
diseases to the proper
agencies.
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World Health Organization
The WHO, a specialized agency of the United Nations, was
founded in 1948. Its missions are to promote technical
cooperation for health among nations, carry out programs to
control and eradicate diseases, and improve the quality of human
life.
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Centers for Disease Control and
Prevention
U.S. Department of Health and Human
Services administers the Public Health Service
and CDC, which assist state and local health
departments in the application of all aspects
of epidemiology.
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The prevention and control of 58
epidemics is a never-ending
community goal.
Effective measures:
• Increase host resistance through the
development and administration of
vaccines that induce active immunity and
maintain it in susceptible persons
• Ensure that persons who have been
exposed to a pathogen are protected
against the disease (e.g., through
injections of gamma globulin or antisera)
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CONT.
Segregate, isolate, and treat those who
have contracted a contagious infection to
prevent the spread of pathogens to others
Identify and control potential reservoirs
and vectors of infectious diseases
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BIOTERRORISM AND
BIOLOGICAL WARFARE AGENTS

GROUP 2 │ ANYAYAHAN, CONTRERAS, OREBILLO, SILVA, VALENCIA

 BIOTERRORISM AND 61
BIOLOGICAL WARFARE AGENTS

In times of war, the use of microorganisms in this

manner is called biological warfare (BW), and
the microbes are referred to as biological
warfare agents.
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Historical Note
Biological Warfare Agents
The use of pathogens as BW agents dates back
thousands of years. Ancient Romans threw carrion
(decaying dead bodies) into wells to
contaminate the drinking water of their enemies.
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Anthrax
Anthrax is caused by B. anthracis, a
spore-forming, Gram- positive bacillus.
People can develop anthrax in several
ways (Fig. 11-8), resulting in three forms
of the disease: cutaneous anthrax,
inhalation anthrax, and gastrointestinal
anthrax.
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Patients with
cutaneous anthrax
develop lesions (Fig.
11-9). Bioterrorists
could disseminate B.
anthracis spores via
aerosols or con-
tamination of food
supplies.
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Botulism
Botulism is a potentially fatal microbial
intoxication, caused by botulinal toxin, a
neurotoxin produced by C. botulinum.
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Smallpox
Smallpox is a serious contagious
disease caused by variola virus, a
member of orthopoxvirus family.
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Historical Note
Smallpox
The WHO was able to eradicate smallpox,
worldwide, by a combination of isolation and
infected vaccination of others in the community.
The last known case persons and of naturally
acquired smallpox in the world occuredin
Somalia in October 1977.
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Historical Note
Black Death
The Black Death, a disease dating back to 100
BC, has killed million of people in Asia and
Europe. The last major epidemic occured in 1721.
Despite the availability of insecticide and
antibiotics, human plague remains rare in the
United States, with only 7 cases in 2007.