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Infection transmission

cycleDr. A. A. Wegdan

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Disease-Transmission

CycleInfection cannot occur unless all key elements are present

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Components of the Infection

Transmission Cycle I. Infectious agent Is the microorganism that can cause infection or

disease.

Includes bacteria, viruses, fungi, and parasites.

II. Reservoir Is the place where the agent survives, grows, and/or

multiplies. People, animals, plants, soil, air, water, instruments

and other items used in clinical procedures

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Components of the Infection

Transmission Cycle III. Place of exit The route by which the infectious agent leaves the

reservoir.

Bloodstream, broken skin, mucous membranes, therespiratory tract, the genitourinary tract, thegastrointestinal tract, the placenta by means of blood,excretions, secretions, or droplets that come from these

sites. For environmental reservoirs, exit may be accomplished

by contamination of patient care equipment bymicroorganisms.

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Components of the Infection

Transmission CycleIV. Mode of transmission

The way in which the infectious agent moves from thereservoir to a susceptible host.

Transmission can occur by 5 modes:1. Contact.

2. Droplet transmission .

3. Airborne transmission .4. Common Vehicle transmission .5. Vector transmission.

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Components of the Infection

Transmission Cycle1. Contact: Is the most important and frequent mode of transmission

of Hospital-acquired infections. The infectious agent can be transmitted directly from the

reservoir to a susceptible host. Through touch or sexual intercourse. It is divided into two subgroups:a) Direct contact: direct body surface-to-body surface

contact and physical transfer of microorganisms.b) Indirect contact: contact of a susceptible host with acontaminated intermediate object, such as contaminatedmedical instruments, needles, or dressings or contaminated gloves.

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Components of the Infection

Transmission Cycle2. Droplet transmission: Occurs via droplets containing microbes generated by

the source when they cough, sneeze, or talk or byrespiratory tract suctioning or bronchoscopy.

Contaminated droplets are propelled through the air ashort distance, and are deposited on the susceptiblehosts conjunctivae, nasal mucosa, or mouth.

Droplets are too heavy to become suspended. Special air handling and ventilation are not necessary to

interrupt droplet transmission.

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Components of the Infection

Transmission Cycle3. Airborne transmission: Infectious agent can be transmitted via tiny droplet

nuclei (< 5 microns) that remain suspended in the air and that can be carried by air currents at greater distances than large droplets.

Droplets are inhaled by the susceptible host. Droplet nuclei may remain suspended in the air for

varying periods of time. Special air handling and ventilation are required in order

to prevent transmission of these microorganisms.

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Components of the Infection

Transmission Cycle4. Common Vehicle transmission: Infectious agent can be transmitted indirectly from the

reservoir to a susceptible host by material

contaminated with the infectious agent. Examples of common vehicles include food, blood,

water, or contaminated instruments and other items.

5. Vector transmission: Infectious agent can be transmitted to a susceptible

host through insects and other invertebrate animals.

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Components of the InfectionTransmission Cycle

V. Place of entry Is the route by which the infectious agent moves into the

susceptible host.

The infectious agent can enter the susceptible hostthrough: Bloodstream. Broken skin.

Mucous membranes. Respiratory tract. Genitourinary tract. Gastrointestinal tract.

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Components of the InfectionTransmission CycleVI. Susceptible host A susceptible host is a person who can become infected

by the infectious agent.

Susceptible hosts include patients, health carepersonnel, ancillary staff, and visitors.

Vaccination to specific agents reduces susceptibility tospecific agents.

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Disease-Transmission

Cycle The most effective method to implement aneffective Infection Control Program is tobreak the disease transmission cycle at any

point.

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