Transcript Introduction to Epidemiology

Introduction to
EPIDEMIOLOGY
Daniel Cothran
BIOL 422 – Microbiology
10/19/2009
Overview
• Introduction to Public Health
• What is Epidemiology?
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History
Who Uses It?
Terminology
Infectious Disease Transmission
The Host Community
Disease Burden
Introduction to Public Health
Introduction to Pubic Health
What is it?
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A field devoted to the promotion and
maintenance of well-being
Attributes
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Multidisciplinary
Often focused on prevention rather than
treatment (upstream)
Operates on multiple levels
Introduction to Public Health (cont’d)
What is Epidemiology?
What is Epidemiology?
Two Definitions:
• “The study of the occurrence, distribution,
and determinants of health and disease in a
population”
• “The study of the distribution and
determinants of disease frequency in human
populations and the application of this study
to control health problems”
History of Epidemiology
• Almost 400 years old!
• “First” epidemiologist:
John Graunt
• William Farr
• Controlled trials! (public
health people love these)
• Shift from studying
infectious to chronic
diseases
• Divergence: molecular
and genetic epidemiology
vs. social epidemiology
Who Uses Epidemiology?
• Health Care Service Providers
• Governments
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Legislature
Health Departments
International Health & Development Agencies
Community-based NGOs
Researchers
Journalists
You
Terminology
Terminology
Terminology (cont’d)
• Case
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An instance of a disease or health condition in an
individual
• Incidence
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Number of new cases of a disease or health condition
in a population over a given period of time
• Prevalence
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Number of new and existing cases of a disease or
health condition in a population over a given time
period
Hand Check!
What’s are the incidence and
prevalence for the class?
• Incidence = _____ /
~70 (per hour)
• Prevalence = ___
+___ /~70 (per hour
Symptoms of Glitter
Disease
Terminology (cont’d)
• Morbidity
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Used commonly to mean illness
Morbidity Rate: refers to the incidence of disease in a
population
• Mortality
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Used commonly to mean death
Mortality Rate: refers to the incidence of death in a
population
➡Morbidity from a disease can be high without
mortality being high
Terminology (cont’d)
• Host – organism capable of supporting the
growth of a virus or other parasite
• Carrier – sub-clinically infected individuals
who may spread a disease
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Examples?
Terminology (cont’d)
• Reservoir – source of viable infectious agents
from which individuals may be infected
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Vector – agent (usually insect or animal) able to
carry pathogens from one host to another
Vehicle – nonliving source of pathogens that infect
large numbers of individuals (food, water, etc)
Terminology (cont’d)
• Zoonosis – a disease, primarily of animals,
that is occasionally transmitted to humans
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Examples: avian and swine flu
Don’t forget to cover your snout when
you sneeze!
Terminology (cont’d)
Disease Progression
• Infection
• Incubation Period
• Acute Period
• Decline Period
• Convalescent Period
Disease Transmission
Direct Host-to-Host Transmission
• Pathogen transmitted
directly from host to
host
Respiratory illnesses
 Sexually-transmitted
infections
 Skin infections
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Vampirism? 
Indirect Host-to-Host Transmission
• Transmitted through living agents (vectors) or
inanimate agents (vehicles)
Mosquito: vector
Lenoir food: vehicle
What type of transmission was at work here?
Epidemics
Common-source epidemic
• Transmission can occur
rapidly
• Classic example: London’s
cholera epidemic in the
1850’s
Epidemics (cont’d)
Host-to-Host Epidemic
• Typically occurs over a longer period of time
than the common-source epidemic
• Examples: Influenza, Chickenpox
Epidemics (cont’d)
The Host Community
Coevolution
• The continued existence of host and pathogen
frequently requires coevolution
• Examples
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Myxoma
Malaria
E. coli
Herd Immunity
Is this what it is?
Herd Immunity (cont’d)
• Resistance of a group to infection due to the
immunity of a high proportion of individuals
• Depends on:
Density of the
population
 Virulence of the
agent
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The Host Community
• Disease is not purely biological!
• Behavior matters
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Examples of protective behaviors?
• Who you are matters
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Racism
sexism
classism
Etc.
Disease Burden
Disease Burden
Disease Burden (cont’d)
Sources
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Aschengrau A, Seage G. Essentials of Epidemiology in Public Health. 2nd Ed. Jones and Bartlett
Publishers, Inc. Salsbury, MA, 2008.
Clark DP, Dunlap PV, Madigan MT, Marinko MM. Brock Biology of Microorganisms. 12th Ed. Pearson
Edu, Inc. San Fransisco, CA, 2009.
http://a3.vox.com/6a00c2252582c1f21900d4144dabbb6a47-500pi
http://himetop.wdfiles.com/local--files/broad-street-pump/Broad%20Street%20Pump.jpg
http://mydogumentary.files.wordpress.com/2009/08/mosquito.jpg
http://farm4.static.flickr.com/3123/2604408184_5718abdaa8.jpg
http://www.independent.co.uk/multimedia/archive/00079/twilight_79981t.jpg
http://images.buyfairycostumes.com/deluxe-fairy-makeup.jpg
http://www.measlesinitiative.org/mi/photos
http://www.whspip.co.uk/images/occu2.jpg
http://www.msf.ca/blogs/cholera/files/2009/03/latrine.jpg
http://www.youtube.com/watch?v=6Pq98sZSBtc
http://www.medicine.manchester.ac.uk/images/epidemiology/home_checkerboard.jpg
http://www.youtube.com/watch?v=LU8DDYz68kM
http://www.dailytarheel.com/content/fewer-h1n1-cases-reported