Infection Control: New York State Mandatory Training

Chapter Two - Element II

Chapter 1: Element I

Chapter 2: Element II

Chapter 3: Element III

Chapter 4: Element IV

Chapter 5: Element V

Chapter 6: Element VI

Chapter 7: Conclusion

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Element II: The modes and mechanisms of transmission of pathogenic organisms in the healthcare setting and strategies for prevention and control.

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 and animals, in soils, food, plants, air or water. The reservoir must meet the needs of the pathogen in order for the pathogen 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).

Chain of Infection

Chain of Infection

Using Avian flu as an example of the chain of infection, the following is currently accepted to be accurate (as of October, 2005):

  • The pathogen is the H5N1 virus.
  • The reservoir is wild migratory waterfowl.
  • The pathogen exits the wild fowl through the feces.
  • It is transmitted through direct contact with infected materials.
  • It enters the susceptible host, in this case, humans, through direct contact with mucous membranes or through small droplet nuclei.

While there have been a number of cases of human to human transmission, as of October, 2005 this has occurred only rarely. However, experts expect that the H5N1 virus will mutate soon making human-to-human transmission common, which may lead to an Avian flu pandemic.

In the healthcare setting the pathogens can be varied. According to JCAHO (2003), in their review of sentinel events related to infection control, common pathogens in a variety of healthcare settings include:

  • Human immunodeficiency virus (HIV);
  • Pseudomonas aeruginosa;
  • Escherichia coli;
  • Methicillin resistant Staphylococcus aureus (MRSA);
  • Salmonella;
  • Clostridium sordellii.

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 coughing, sneezing or talking from an infected person and propelled a short distance.
  • Inhalation of airborne microorganisms that remain suspended in the air.

More than 8 million U.S. healthcare workers in hospitals may be exposed to blood or other body fluids through the following types of contact (NIOSH, 2004):

  • Percutaneous injuries (injuries through the skin) with contaminated sharp instruments such as needles and scalpels (82%)
  • Contact with mucous membranes of the eyes, nose, or mouth (14%)
  • Exposure of broken or abraded skin (3%)
  • Human bites (1%)

Up to 800,000 percutaneous injuries may occur annually among all U.S. healthcare workers (both hospital-based workers and those in other health care settings). After percutaneous injury with a contaminated sharp instrument, the average risk of infection is 0.3% for HIV and ranges from 6% to 30% for HBV (NIOSH, 2004).

During the period 1995-2000, there were 10,378 reported percutaneous injuries among hospital workers. The devices most associated with percutaneous injuries among hospital workers during 1995-2000 were hypodermic needles (29% of injuries), suture needles (17%), winged steel needles (12%), and scalpels (7%). Other hollow-bore needles together accounted for 19% of injuries, glass items for 2%, and other items for 14% (NIOSH, 2004).

During the period 1995-2000 there were 6,212 reported percutaneous injuries involving hollow-bore needles in hospital workers. Drawing blood from a vein (venipuncture) was responsible for 25% of percutaneous injuries involving hollow-bore needles during 1995-2000, and injections were responsible for 22% (NIOSH, 2004).

There are a number of different precautions that healthcare workers must utilize to protect against infectious organisms. The most widely accepted method is standard precautions.

Standard precautions are largely based on the previous Universal Precautions, which referred to the concept of bloodborne disease control which requires that all human blood and certain human body fluids are treated as if known to be infectious for HIV, HBV, and other bloodborne pathogens (CDC, 2004a; OSHA, 2003). The use of standard precautions assumes that the blood or body fluids of any person could be infectious, therefore personal protective equipment (PPE) is needed as a barrier to transmission of infectious agents. Decisions about the use of PPE are determined by the type of interaction the healthcare worker has with the patient (CDC, 2004a).

PPE for standard precautions include (CDC, 2004a):

  • Gloves when touching blood, body fluids, secretions, excretions, contaminated items, for touching mucus membranes and non-intact skin.
  • Gowns during procedures and patient care activities when contact of clothing/exposed skin with blood/body fluids, secretions, or excretions is anticipated.
  • Mask and goggles or a face shield during patient care activities likely to generate splashes or sprays of blood, body fluids, secretions or excretions.

Expanded Precautions include the following:

  • Contact Precautions
  • Droplet Precautions
  • Airborne Precautions

PPE for contact precautions include: gowns and gloves for contact with patient or environment of care (e.g. medical equipment, environmental surfaces). In some instances gowns are required when entering a patient's environment.

PPE for droplet precautions: surgical masks within three feet of patient.

PPE for airborne precautions: particulate respirator. In addition positive pressure isolation room is also needed (but this is an engineering control discussed in Element III of this course.

Continue on to Chapter 3: Element III