principles of epidemiology
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Principles of Epidemiology
www.doh.state.fl.us
Studying DiseasePathology
Study of disease
EpidemiologyStudy of the frequency and distribution
of diseaseEpidemiologist – “disease detective”
Work to prevent, control, and eradicate diseases
What does an epidemiologist have to consider in today’s world when
studying human disease?
Do you speak my language?(Or rather the
epidemiologist’s language)
Endemic DiseasesDiseases that are always present in a
population of a particular geographic region
Examples (in U.S.):TuberculosisChickenpoxInfluenzaMumpsPlague (not in human populations)
Epidemic DiseasesAn unusually large number of
disease cases in a population in a particular region
Usually occur within a relatively short period of a time
Ex. Influenza Ex. Ebola virus in Africa
Zoonotic DiseasesInfectious diseases that humans
acquire from animal sourcesEx. Ebola virusEx. Plague (Yersinia pestis)
Chimpanzee – ebola virus host. www.primates.com
Prairie Dogs – carriers of plague. www.nps.gov
Legionnaire’s Disease - EpidemicType of bacterial
pneumonia (Legionella pneumophila)
First described in 1976 after an outbreak during an American Legion convention in Philadelphia
How did this happen?
Sporadic DiseaseA disease that occurs only
occasionally within a population of a particular geographic region.
Ex. Tetanus, plague, botulism, cholera
Disease TransmissionCommunicable Disease
Disease that is transmitted from human to human.
Noncommunicable DiseaseDiseases that are nontransmissible.
Ex. Botulism from ingestion of tainted foodContagious Disease
A communicable disease that is easily transmitted from person to person.Ex. Influenza
Terms Concerned With the Rate of Disease
Incidence Rate# of new cases in a specific time period in a given
population
Prevalence Rate# of total existing cases in a population
Morbidity Rate# of new cases of a particular disease that occurred during
a specified time period per a specifically defined population
Mortality RateFraction of people who die from a disease
Pandemic DiseaseA disease that occurs in epidemic
proportions in many countries or sometimes worldwide.
Examples: HIV/AIDSTuberculosisMalaria
Factors Affecting InfectionCharacteristics of the:
Pathogen
Host
Environment
Factors Concerning the Pathogen
Virulence of pathogen
How pathogen enters body
Number of organisms that enter the body
Factors Concerning the Host
Health of individual
Nutrition of individual
Behavior of individual
Factors Concerning the Environment
Characteristics of geographic location
A sufficient reservoir for pathogens and appropriate carriers of a disease
Sanitary conditions
Access to drinkable water
Chain of Infection
safetydrs.blogspot.com
www.thorstenconsulting.com www.ericmstrauss.com
Reservoirs of InfectionAny site where a pathogen can
multiply and survive until it is transferred to a host.
Living ReservoirsAnimal/Human carriers
Nonliving ReservoirsAir, soil, dust, food, milk, water, fomites
Types of CarriersPassive Carrier
Carry pathogen without ever having had diseaseIncubatory Carrier
Able to transmit pathogen during incubation period
Convalescent CarrierTransmit a pathogen while recovering from a
diseaseActive Carrier
Recovered from a disease but continue to carry pathogen indefinitely
Modes of TransmissionDirect Contact
Skin-to-skin contactMucous membrane-to-mucous membrane contact
Indirect ContactAirborne droplets that contain respiratory secretions
from sneezing or coughingFood and water contaminated by fecal material.Arthropod vectors (ticks, fleas, lice, mosquitoes, flies,
mites)From fomitesTransfusion of contaminated blood or blood products
Public Health Agencies
World Health Organization (WHO)
Centers for Disease Control and Prevention (CDC)
The End
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