The Chain of Infection is a basic component of understanding
the prevention and control of infection that most healthcare
workers recall from their early days of training. It is a
critical concept in infection control that is worth reviewing:
The pathogen is the micro-organism that causes infection
such as bacteria, viruses, fungi and parasites. There must
be an adequate number of pathogens to cause disease.
The reservoir is the place where micro-organisms live,
such as in humans, animals, soils, food, plants, air or water.
In the dental workplace, the most common reservoirs are humans,
water and dental equipment. The reservoir must meet the needs
of the pathogen in order to survive and multiply.
The means of exit are how the micro-organism leaves
The method of transmission is how the pathogen moves
from place to place.
The means of entry is how the microorganism enters
The susceptible host is the person who may become
infected. The host cannot have immunity to the pathogen such
as may occur through previous infection with the pathogen
or through immunization.
The occurrence and presence of all these factors and events
is considered the "chain of infection". In the healthcare
setting, all of these factors come into play in the spread
and the control of infection. Effective infection control
strategies prevent disease transmission by interrupting one
or more links in the chain of infection (CDC, 2003.)
Common modes of transmission of pathogens
in the healthcare setting include:
- Direct contact of intact or non-intact skin with blood
or body fluids or other potentially infectious material.
- Indirect contact with contaminated instruments or environmental
- Contact of mucous membranes of the eyes, nose or mouth
with droplets or spatter containing pathogens that are generated
through dental handpiece and water/air syringe aerosols,
coughing, sneezing or talking from an infected person and
propelled a short distance.
- Inhalation of airborne microorganisms that remain suspended
in the air.
Dental patients and dental professionals may be exposed to
a variety of disease-causing microorganisms that are present
in the mouth and respiratory tract. These organisms may be
transmitted in dental settings through several routes, including:
- Intact or non-intact skin.
- Contact with a contaminated object (e.g., instruments,
operatory equipment, or environmental surfaces).
- Contact with mucous membranes of the eyes, nose, or mouth.
with droplets (e.g., spatter) containing microorganisms
generated (e.g., dental procedural splatter, coughing, sneezing,
talking) from an infected person and propelled a short distance.
Inhalation of airborne microorganisms that can remain suspended
in the air for long periods of time (e.g. aerosols from
dental handpieces and air/water syringes).
These organisms can be transmitted in dental settings through:
- Direct contact with blood, oral fluids, or other patient
- . Indirect contact with contaminated objects (e.g., instruments,
equipment, or environmental surfaces);
- Contact of conjunctival, nasal, or oral mucosa with droplets
(e.g., spatter) containing microorganisms generated from
an infected person and propelled a short distance (e.g.,
by coughing, sneezing, or talking); and
- Inhalation of airborne microorganisms that can remain
suspended in the air for long periods.
Types of Microorganisms & Chemical
The following chart of microorganisms is organized from most
difficult to kill on surfaces or instruments to least difficult
Resistance to Chemical Disinfectant (OSU,
|NONLIPID OR SMALL VIRUSES
||Pseudomonas aeruginosa Staphylococcus
|LIPID OR MEDIUM-SIZE VIRUSES
||Herpes simplex virus
Respiratory syncytial virus
Hepatitis B virus
Human Immunodeficiency virus
Continue on to Strategies
and Controls that Limit Exposure to Infection