The Infectious Disease Process
by: Franz
· An infection is the result of the invasion of a pathogen, a microorganism that can cause disease, into a host.
· Disease result when the normal tissue function is impaired.
· Transmission of pathogen is accomplished by an infectious source, a vector of spread and a susceptible host.
· Six components of the infectious disease process. Also known as the Chain of Infection.
o Causative agent
o Reservoir
o Portal of exit from reservoir
o Mode of transmission
o Portal of entry into host
o Susceptible host
· Infection control strategies are based on breaking the chain.
1. Causative Agent
Types:
-
- Bacterium
- Virus
- Fungus
- Parasites
- Rickettsia
- Helminthes
- Prion
Characteristics:
-
- Pathogenicity – ability to cause disease
- Virulence – disease severity – invasiveness – ability to enter and move through tissue
- Infectious dose – number of organism needed to initiate infection
- Organism specificity – host preference
- Antigenic variations – viral genetic recombinations
- Toxigenicity – capacity to produce toxins (poisonous substances)
- Ability to develop resistance to antimicrobial agents
2. Reservoir
The environment in which the infectious agent lives and multiplies
-
- Human – symptomatic case of measles, person with tuberculosis
- Animal – Rocky Mountain spotted fever from ticks, malaria from mosquitoes, rabies from bats and dogs
- Environment/Fomites – dust, garden soil, contaminated water
3. Portal of exit from reservoir
Paths by which infectious agent leaves the reservoir
-
- Respiratory tract (most common path in human)
- GI tract
- Genitourinary (GU) tract
- Skin – open lesion
- From bloodstream or tissue by insect bites, hypodemic needles or surgical instrument
4. Mode of transmission
There are four (4) main routes of transmission
a. Contact Transmission
o Direct contact – person to person
o Indirect contact – usually in inanimate object
o Droplet contact – large particles from coughing, sneezing, or talking by an infected person
b. Common Vehicle Route (through contaminated objects)
o Food – salmonellosis
o Water – shigellosis, legionellosis
o Drugs – bacteria resulting from infusion of contaminated infusion product
o Blood – hepatitis B
c. Airborne Transmission
o Droplet nuclei – residue of evaporated droplets that remain suspended in air
o Dust particles in the air containing the infectious agent
d. Vector-borne Transmission
o Mechanical or biological spread from vectors, such as flies, mosquitoes, ticks and rats
5. Portal of entry into host
Paths by which infectious agent enters the human body.
o Respiratory tract
o GI tract
o GU tract
o Direct infection of mucous membrane/break in the skin
a. Parenteral (via blood)
b. Transplacental – from mother to fetus
c. Conjunctiva
6. Susceptible host
a. One who lack effective resistance to infectious agent
b. Factors: influencing susceptibility:
o Number of organism to which host is exposed; duration of exposure
o Age, genetic constitution of host, and general physical, mental and emotional health and nutritional status of host
o Status of hematopoietic system; efficacy of reticuloendothelial system
o Absence of abnormal immunoglobulins
o The number of T lymphocytes and their ability to function
CARE FOR PATIENT WITH COMMUNICABLE DISEASE
