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EPIDEMIOLOGY
words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of.
EPIDEMIOLOGY
the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.
EPIDEMIOLOGY
Study of interrelationship of factors in particular areas in the field of health, and the application of the results of such studies to influence such factors to achieve a given outcome
CHAIN OF INFECTION
Traditional epidemiologic triad model holds that infectious diseases result from the interaction of agent, host, and environment
CHAIN OF INFECTION
Transmission occurs when the agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host.
Agent
virulence
Agent
infectivity of the pathogen
Agent
addictive quality of a substance of abuse
Host
genetic susceptibility
Host
resiliency
Host
nutritional status
Host
behavior
Environment
availability of healthcare
Environment
sanitary conditions
Environment
social context
EPIDEMIOLOGY
Study of ecology of health and disease, and the application of knowledge gained to promote health and control diseases.
AGENT
Any element, substance, or force whether living or non-living, the presence or absence which can initiate or perpetuate a disease process.
AGENT
Could be physical and mechanical in nature Chemicals
Exogenous
(common poisons)
Endogenous
(accumulation of toxic products)
INHERENT CHARACTERISTICS OF AGENTS
Physical features, biologic requirements, chemical make-up, viability, and resistance.
CHARACTERISTICS IN RELATION TO THE ENVIRONMENT
Refers to the reservoir and sources of infection and modes of transmission.
Antigenicity
to induce immune response
Virulence
refers to the severity of the reaction produced and is usually measured in terms of fatality.
Pathogenicity
measures the ability of an agent when lodged in the body to set-up a specific reaction, local or general, clinical or sub-trial.
RESERVOIR
The habitat in which the agent normally lives, grows, and multiplies.
HUMAN RESERVOIR
Many common infectious diseases have human reservoirs. For example, sexually transmitted diseases, measles, mumps, streptococcal infection, and many respiratory pathogens.
ENVIRONMENTAL RESERVOIR
Plants, soil, and water in the environment are also reservoirs for some infectious agents.
Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil.
Zoonosis
Refers to an infectious disease that is transmissible under natural conditions from vertebrate animals to humans.
ANIMAL RESERVOIR
Many of these diseases are transmitted from animal to animal, with humans as incidental hosts
Direct contact
Occurs through skin-to-skin contact, kissing, and sexual intercourse.
Droplet spread
Refers to spray with relatively large, shortrange aerosols produced by sneezing, coughing, or even talking.
Indirect transmission
Refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors)
Airborne transmission
Occurs when infectious agents are carried by dust or droplet nuclei suspended in air.
Vehicle-borne
May indirectly transmit an infectious agent include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). A vehicle may passively carry a pathogen — as food or water may carry hepatitis A virus.
Vector-borne
Such as mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent.
PORTAL OF ENTRY
The portal of entry refers to the manner in which a pathogen enters a susceptible host. The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act.
HOST
The final link in the chain of infection is a susceptible host. Susceptibility of a host depends on genetic or constitutional factors, specific immunity, and nonspecific factors that affect an individual’s ability to resist infection or to limit pathogenicity. An individual’s genetic makeup may either increase or decrease susceptibility.
