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