Download Principles of Disease and Epidemiology

Principles of Disease
and Epidemiology
How do we know you are sick let
alone that its an epidemic?
Defining Some Terms
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Pathology
Study of disease
Etiology
Study of the cause of a disease
Pathogenesis Development of disease
Infection
Colonization of the body
by pathogens
Disease
An abnormal state in which the
body is not functionally normally
Symbiosis
•
Symbiosis is the relationship between
organisms living together
•
Commensalism
•
•
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Mutualism
•
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one organism is benefited
the other is unaffected.
both organisms benefit.
Parasitism
•
one organism is benefited at the expense of the
other.
You as Ecosystem
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Transient microbiota may be present
for days, weeks, or months
Normal microbiota permanently colonize
the host
Some normal microbiota are
opportunistic pathogens.
Normal Microbiota and the
Host:
•
Locations of
normal
microbiota on
and in the
human body
Figure 14.2
Normal Microbiota and the
Host:
Normal microbiota protect the host by:
occupying niches that pathogens might occupy
 producing acids
 producing bacteriocins
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Probiotics are live microbes applied to or
ingested into the body, intended to exert
a beneficial effect.
Some Normal Flora
Koch’s Postulates
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Koch's
Postulates
are used to
prove the
cause of an
infectious
disease.
Figure 14.3.1
Koch’s Postulates
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Koch's
Postulates
are used to
prove the
cause of an
infectious
disease.
Figure 14.3.2
Classifying Infectious
Diseases
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Symptom
A change in body function
that is felt by a patient as a
result of diisease
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Sign
A change in a body that can be
measured or observed as a result
of disease.
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Syndrome
A specific group of signs and
symptoms that accompany a
disease.
Classifying Infectious
Diseases
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Communicable disease
spread from one host to
another.
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Contagious disease
easily spread from one
host to another.
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Noncommunicable disease
not transmitted
from one host to
another.
Occurrence of Disease
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Incidence
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Prevalence
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Sporadic disease
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Endemic disease
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Epidemic disease
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Pandemic disease
Fraction of a population that
contracts a disease during a
specific time.
Fraction of a population having
a specific disease at a given time.
Disease that occurs
occasionally in a population.
Disease constantly present in a
population.
Disease acquired by many
hosts in a given area in a short
time.
Worldwide epidemic.
Severity or Duration of a
Disease
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Acute disease
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Chronic disease
Subacute disease
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Latent disease
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Symptoms develop
rapidly
Disease develops slowly
Symptoms between
acute and chronic
Disease with a period of
no symptoms when the
patient is infective
The Stages of a Disease
Figure 14.5
Reservoirs of Infection
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Reservoirs of infection are continual
sources of infection.
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Human — AIDS, gonorrhea
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Animal — Rabies, Lyme disease
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Carriers may have inapparent infections or latent
diseases
Some zoonoses may be transmitted to humans
Nonliving — Botulism, tetanus
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Soil
Reservoirs of Infection
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Reservoirs of infection are continual
sources of infection.
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Human — AIDS, gonorrhea
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Animal — Rabies, Lyme disease
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Carriers may have inapparent infections or latent
diseases
Some zoonoses may be transmitted to humans
Nonliving — Botulism, tetanus
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Soil
Transmission of Disease
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Contact
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Direct
Indirect
 Droplet
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Requires close association between
infected and susceptible host
Spread by fomites
Transmission via airborne droplets
Transmission of Disease
Figure 14.6a & 8
Transmission of Disease
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Vehicle
Transmission by an inanimate
reservoir (food, water)
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Vectors
Arthropods, especially fleas, ticks,
and mosquitoes
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Mechanical Arthropod carries pathogen on
feet
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Biological
Pathogen reproduces in
vector
Transmission of Disease
Figure 14.6b, c
Nosocomial (Hospital-Acquired)
Infections
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Are acquired as a result of a hospital stay
5-15% of all hospital patients acquire
nosocomial infections
Figure 14.7, 9
Relative frequency of
nosocomial infections
Figure 14.10
Common Causes of
Nosocomial Infections
Percentage of
nosocomial
infections
Percentage
resistant to
antibiotics
Gram + cocci
34%
28%-87%
Gram – rods
32%
3-34%
Clostridium
difficile
17%
Fungi
10%
Emerging Infectious
Diseases
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Diseases that are new, increasing in incidence, or
showing a potential to increase in the near future.
Contributing factors:
 Evolution of new strains
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Inappropriate use of antibiotics and pesticides
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V. cholerae O139
Antibiotic resistant strains
Changes in weather patterns
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Hantavirus
Emerging Infectious
Diseases
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Contributing factors:
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Modern transportation
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Ecological disaster, war, expanding human
settlement
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Coccidioidomycosis
Animal control measures
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West Nile virus
Lyme disease
Public Health failure
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Diphtheria
Epidemiology
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The study of
where and when
diseases occur
Figure 14.11
Principles of Disease
Surveillance
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www.who.int/emc/slideshows/Survintro/sld001.htm
Epidemiology
John Snow
1848-1849
Mapped the occurrence
of cholera in London
Ignaz
Semmelweis
1846-1848
Showed the hand
washing decreased the
incidence of puerperal
fever
Florence
Nightingale
1858
Showed that improved
sanitation decreased the
incidence of epidemic
typhus
Methods
• Descriptive
Collection and analysis of
data regarding occurrence
of disease
Snow
• Analytical
Comparison of a diseased
group and a healthy group
Nightingale
• Experimental
Study of a disease using
controlled experiments
Semmelweis
• Case reporting
Health care workers report
specified disease to local,
state, and national offices
• Nationally
Notifiable
Diseases
Physicians are required to
report occurrence
Table 14.7
Centers for Disease Control and
Prevention (CDC)
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Collects and analyzes epidemiological information
in the U.S.
Publishes Morbidity and Mortality Weekly Report
(MMWR) www.cdc.gov
Morbidity: incidence of a specific notifiable disease
Mortality: deaths from notifiable diseases
Morbidity rate = number of people affected/total
population in a given time period
Mortality rate - number of deaths from a
disease/total population in a given time
CDC and MMWR
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Centers for Disease Control and
Prevention
Morbidity and Mortality Weekly Report
Published by the CDC
 Weekly information on reportable diseases
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