California Dental Board Approved: Infection Control (2 Units)

The Chain of Infection

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 reservoir.

The method of transmission is how the pathogen moves from place to place.

The means of entry is how the microorganism enters the host.

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 surfaces.
  • 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:

  1. Direct contact with blood, oral fluids, or other patient materials;
  2. . Indirect contact with contaminated objects (e.g., instruments, equipment, or environmental surfaces);
  3. 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
  4. Inhalation of airborne microorganisms that can remain suspended in the air for long periods.

Types of Microorganisms & Chemical Disinfectant Resistance

The following chart of microorganisms is organized from most difficult to kill on surfaces or instruments to least difficult to kill.

Table 1. Resistance to Chemical Disinfectant (OSU, 2011)



Most Resistant

Least Resistant

BACTERIAL SPORES Bacillus subtilis
Clostridium sporogenes
MYCOBACTERIA Mycobacteriumtuberculosis;
M. bovis
FUNGI Trichophyton sp.
Cryptococcus sp.
Candida sp.
VEGETATIVE BACTERIA Pseudomonas aeruginosa Staphylococcus aureus
Salmonella choleraesuis
Respiratory syncytial virus
Hepatitis B virus
Human Immunodeficiency virus

Continue on to Strategies and Controls that Limit Exposure to Infection