Download Airgas template - York Technical College

Burton's Microbiology
for the Health Sciences
Chapter 11.
Epidemiology and Public Health
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 11 Outline
• Epidemiology
• Interactions Among Pathogens, Hosts and the
Environment
• Chain of Infection
• Reservoirs of Infection
• Modes of Transmission
• Public Health Agencies
• Bioterrorism and Biological Warfare Agents
• Water Supplies and Sewage Disposal
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Epidemiology
• Introduction
– Epidemiology can be loosely
defined as the study of
disease.
– Epidemiologists study the
factors that determine the
frequency, distribution, and
determinants of diseases in
human populations.
– Epidemiologists also develop
ways to prevent, control, or
eradicate diseases in
populations.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Epidemiologic Terminology
• A communicable disease is an
infectious disease that can be
transmitted from one person to another
• A contagious disease is a
communicable disease that is easily
transmitted from person-to-person.
• Zoonotic diseases are diseases that
humans acquire from animal sources.
• The incidence of a particular disease is
the number of new cases of that
disease in a defined population during
a specific time period.
• The morbidity rate is the 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).
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Epidemiologic Terminology
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Epidemiologic Terminology, cont.
• Prevalence
–
Period prevalence is the
number of cases of a disease
existing in a given
population during a specific
time period (e.g., during the
year 2009).
–
Point Prevalence is the
number of cases of a disease
existing in a given
population at a particular
moment in time (e.g., right
now).
• Mortality rate is the ratio of the
number of people who died of a
particular disease during a
specified time period per a
specified population
HIV Prevalence
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Epidemiologic Terminology, cont.
• A sporadic disease is one that
occurs only occasionally within
the population of a particular
geographic area; example,
tetanus.
• An endemic disease is one that
is always present within the
population of a particular
geographic area; example,
gonorrhea.
• An epidemic disease is defined
as a greater than usual number
of cases of a disease in a
particular region, usually within
a short period of time; example,
the Legionnaire’s disease
epidemic of 1976.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
http://news.bbc.co.uk/2/hi/health/6959583.stm
Epidemiologic Terminology, cont.
• A pandemic is a disease
that is occurring in
epidemic proportions in
many countries
simultaneously. Examples
include:
– Influenza
• Examples: (1) the
Spanish flu
pandemic of 1918
during which more
than 20 million
people were killed
worldwide
(500,000 in the
U.S.); (2) the
H1N1 (“swine flu”)
pandemic of 20092010.
– HIV/AIDS
– Tuberculosis
– Malaria
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Interactions Among Pathogens,
Hosts, and the Environment
• Whether an infectious disease
occurs depends on:
–
Factors pertaining to the
pathogen (e.g., virulence of
pathogen, mode of entry,
number of organisms)
–
Factors pertaining to the
host (e.g., health status,
nutritional status, hygiene,
age, travel, lifestyle, etc.)
–
Factors pertaining to the
environment (e.g., physical
factors such as climate,
season, geographic
location; availability of
appropriate reservoirs;
sanitary and housing
conditions; and availability
of potable water
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
The Chain of Infection
There are 6
components in
the infectious
disease process:
● a pathogen
● a source of
the pathogen (a
reservoir)
● a portal of
exit
● a mode of
transmission
● a portal of
entry
● a susceptible
host
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Reservoirs of Infection
• The sources of
microorganisms that cause
infectious diseases are many
and varied; they are known as
reservoirs of infection or
simply reservoirs.
– Living reservoirs –
humans, pets, farm
animals, insects,
arachnids
– Human carriers:
• Passive carriers
• Incubatory carriers
• Convalescent carriers
• Active carriers
“Typhoid Mary”
http://www.trutv.com/library/crim
e/criminal_mind/forensics/typhoid
_mary/8.html
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Reservoirs of Infection, cont.
• Animals
– Infectious diseases
that humans acquire
from animal sources
are called zoonotic
diseases or zoonoses.
– Zoonoses may be
acquired by direct
contact with an
animal, inhalation or
ingestion of the
pathogen, or injection
of the pathogen by
an arthropod.
• Examples:
• Rabies
• Lyme disease
• Many others
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Reservoirs of Infection, cont.
• Arthropods
–
Many different types of
arthropods serve as
reservoirs of infection,
including insects (e.g., fleas,
mosquitoes, lice) and
arachnids (e.g., mites and
ticks)
–
When arthropods are
involved in the transmission
of infectious diseases they
are referred to as vectors.
• Examples of arthropodborne diseases:
• Lyme disease
• Malaria
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Reservoirs of Infection, cont.
• Nonliving Reservoirs
– Air, soil, dust,
contaminated
water and foods,
and fomites
– Fomites inanimate objects
capable of
transmitting
pathogens (e.g.,
bedding, towels,
eating and drinking
utensils, hospital
equipment,
telephones,
computer
keyboards, etc.)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Inanimate Vectors of Infection (Fomites)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Most Common Modes of Transmission
of Infectious Diseases
• Direct skin-to-skin contact
• Direct mucous membrane-tomucous membrane contact by
kissing or sexual intercourse
• Indirect contact via airborne
droplets of respiratory
secretions, usually produced by
sneezing or coughing
• Indirect contact via food and
water contaminated by fecal
matter
• Indirect contact via arthropod
vectors
• Indirect contact via fomites
• Indirect contact via transfusion
of contaminated blood or blood
products or by parenteral
injection using nonsterile
syringes or needles
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Public Health Agencies
• World Health Organization
(WHO)
–
A specialized agency of the
United Nations founded in
1948; www.who.org
–
Missions: to promote
technical cooperation for
health among nations; to
carry out programs to
control and eradicate
diseases; to improve the
quality of human life
• Investigates outbreaks
of Ebola virus, etc.
• Eradicated smallpox
• Attempting to eradicate
polio and dracunculiasis
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Public Health Agencies, cont.
• Centers for Disease Control
and Prevention (CDC)
– A federal agency
administered by the U.S.
Department of Health and
Human Services; located
in Atlanta, GA; established
in 1946; www.cdc.gov
– Certain infectious
diseases, known as
nationally notifiable
diseases must be reported
to the CDC.
– Publishes Morbidity and
Mortality Weekly Report
(MMWR).
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
http://www.cdc.gov/obesity/data/index.html
Public Health Agencies, cont.
• Measures for prevention and
control of epidemics:
– Increase host resistance
through the development and
administration of vaccines
that induce active immunity
and maintain it in susceptible
persons
– Ensure that persons exposed
to a pathogen are protected
against the disease
– Segregate, isolate and treat
those who have contracted a
contagious infection to
prevent the spread of the
pathogen to others
– Identify and control potential
reservoirs and vectors of
infectious diseases
http://www.meningvax.org/cont
rol-epidemics.php
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Bioterrorism and Biological
Warfare Agents
• Microbes purposely used to harm others in wartime are
called biological warfare (bw) agents.
• Pathogens used to create fear, chaos, illness, and death
in situations other than war are called bioterrorism
agents. Examples:
– Bacillus anthracis (the cause of anthrax)
– Clostridium botulinum (the cause of botulism)
– Smallpox virus (Variola major)
– Yersinia pestis (the cause of plague)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Water Supplies and Sewage Disposal
• Water is the most essential
resource necessary for the
survival of humanity!
• The 2 general types of
water pollution:
– Chemical pollution
– Biological pollution
(e.g., fecal material
and garbage)
• The 1993 cryptosporidiosis
epidemic in Milwaukee, WI,
was the largest waterborne
epidemic in the U.S.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Water Supplies and Sewage Disposal,
cont.
• Water Treatment
–
The major steps in water
treatment are sedimentation,
coagulation, filtration, and
chlorination
–
Water is tested for fecal
contamination by checking for
the presence of coliform bacteria
(coliforms), such as E. coli and
other members of the family
Enterobacteriaceae
• Sewage Treatment
–
Raw sewage consists mainly of
water, fecal material, garbage,
and bacteria
–
Includes primary, secondary,
and tertiary sewage treatments
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins