The Chain of Infection Transmission

Chain of Infection Transmission


Understanding the chain of infection can help healthcare professionals develop and implement policies and procedures aimed at reducing the risk of infection transmission.  Properly performing cleaning and decontamination in healthcare facilities is essential in the prevention of transmission of diseases from one person to another.    

Healthcare-care-associated infections or HAIs (formally termed nosocomial infection) are those infections that patients acquire after being admitted and were not developing at the time of admission to the healthcare facility.

Six main factors make up the chain of infection: the etiologic agent, a reservoir, the portal of exit, the mode of transmission, the portal of entry, and a susceptible host.  All six of these factors are vitally important and must be present for an infection to take place.  The chain of infection includes the:

  1. Etiologic agent such as bacterium, virus, fungus, or other microorganism.  The infectious agent must be present and pathogenic (capable of causing disease) and in an infectious dose (minimum number needed to cause disease).
  2. Presence of a reservoir or source that will allow the microbes to survive.  Frequent reservoirs include supplies and equipment (e.g. surgical instruments) used in patient care as well as food and drink, linen, and other inanimate objects.  Patients themselves play a significant role in the infection transmission.
  3. Portal of exit which is the source that allows the pathogen to emerge. These portals of exit include the respiratory tract, blood vascular system, skin, and mucous membranes, as well as the gastrointestinal and genitourinary tracts. Contact with patient care supplies and equipment and instruments will most likely result in potential contamination and the possibility of disease transfer.
  4. The chief mode of disease transfer is the contact  transmission, either through direct or indirect contact with the patient or through droplet spread via contact with respiratory secretions. Direct-contact transmission involves person-to-person spreading such as improperly cleaned and disinfected devices or contact with the unwashed hands of a healthcare provider.
  5. Portal of entry, or how the pathogens gain entry into the body.  The portal of entry is very similar to the portals of exit.
  6. The susceptible host, someone who does not have effective resistance to the pathogenic agent they are exposed to.  Most transmissions require some breach of skin integrity.

Healthcare professionals play a major role in the prevention of disease transmission.  Proper reprocessing of reusable medical devices is a vital role in the prevention of HAIs.


ST79 – Comprehensive guide to steam sterilization and sterility assurance in health care facilities, ANSI/AAMI ST79:2010 & A1:2010 & A2:2011 & A3:2012 & A4:2013