MLSP WEEK 14

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.