Week 1 (Part 2): Infection Transmission Flashcards
What are the 6 steps of the Chain of Infection?
1) Reservoir
2) Portal of Exit
3) Mode of Transmission
4) Portal of Entry
5) Susceptible Host
6) Infectious Agent
The traditional epidemiologic triad model holds that infectious diseases result from (3) :
The interaction of:
- agent
- host
- environment
When does transmission occur? (3)
Transmission occurs when:
- the agent leaves itsreservoiror host through aportal of exit
- is conveyed by somemode of transmission
- and enters through an appropriateportal of entryto infect asusceptible host
Chain of Infection:
- Describe the reservoir
- The habitat in which the organism normally lives, grows, and multiplies
- There can be human reservoirs, animal reservoirs or environmental reservoirs
Chain of Infection:
- Describe the Portal of Exit
The portal of a pathogens tend to be the same as portals of entry (or where they tend to be localized)
- pathogens often leave hosts in materials the body secretes/excretes
Chain of Infection:
- Describe the (5) types of Mode of Transmission
a) Physical contact – direct person to person contact, whether skin to skin, kissing, or sexual intercourse ie) STIs, cold sores, HPV
b) Vehicle borne - is where the pathogen is transmitted from source to susceptible host via intermediate object (fomites), as well as food and water
c) Airborne - occurs when infectious agents are carried by dust or droplet nuclei suspended in air, which can sometimes by for a long time and can be blown over large distances
d) Droplets – large spray with short-range aerosols produced by sneezing coughing or even talking etc. which are sprayed only a few feet before dropping to the ground
e) Vector borne – animal or insect
Chain of Infection:
- Describe the 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.
Chain of Infection:
- Describe the Host Susceptibility
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.
How is the chain of infection broken? (5)
Transmission may be interrupted when:
1) The infectious agent is eliminated, inactivated or cannot survive in the reservoir (E.g. rapid identification and management of organisms, cleaning and disinfecting of the environment)
2) The portal of exit is managed through good infection prevention and control practices (E.g. Hand Hygiene, appropriate use of PPE, safe packaging and disposal of waste)
3) Transmission does not occur due to good infection prevention and control practices (E.g. Hand Hygiene, isolation of infected patients, air flow control where appropriate)
4) The portal of entry is protected (E.g. Aseptic non-touch technique, safe catheter care, wound care)
5) Reducing the susceptibility of patients receiving healthcare (E.g. Treatment of underlying disease, recognising high risk patients)
Interventions aimed at breaking the chain of infection are directed at (3):
1) Controlling or eliminating agent at source of transmission
2) Protecting portals of entry
3) Increasing host’s defenses
What are emerging barrier to decreasing disease transmission (6):
1) Increases in host susceptibility due to changes in demographics and behaviour
2) Microbial adaptation and change (ie drug resistance, or pathogen mutation)
3) Emergence of new diseases
4) Breakdown of public health measures
5) International travel and commerce
6) Changes in the environment, technology and industry practices
Define infection:
- How is it distinguished from disease?
Infection is the invasion of the host by microorganisms, which then multiply in close association with the host’s tissues.
- Infection is distinguished from disease, a morbid process that does not necessarily involve infection (diabetes, for example, is a disease with no known causative agent).
The Host pathogen Relationship is dependent on 3 main factors:
1) Number of organisms in or on the host
– in most cases, the higher the number, the greater the risk to the host
2) The virulence of the organism which is the capacity of a pathogen to cause disease
- Pathogen infectivity generally results from a disturbance in the balance between pathogen virulence and host resistance
3) Host defenses and resistance, which can also be reversed to look at the host’s susceptibility to infection
- Obviously defenses are protective, while susceptibility factors put the host at risk.
Virulence factors should never be considered independently of? Why?
The host’s defenses
- The clinical course of an infection often depends on the interaction of virulence factors with the host’s response
- An infection begins when the balance between pathogenicity and host resistance is upset
Why do some pathogens cause disease and others don’t?
Provide examples:
Virulence! The ability of an organism to cause infectious disease
- Some infectious agents are easily transmitted (very contagious), but they are not very likely to cause disease (not very virulent)
- Other infectious agents are very virulent, but not terribly contagious
Example 1: Polio infects most people who contract it but only 5-10% of those infected will actually develop clinical disease
Example 2: Ebola virus virulence is very high (50-90% fatality rate among those infected); however virus not transmitted easily by casual contact
Example 3: Most worrisome infectious agents are those that are both very contagious and very virulent (COVID)
