Chain of infection, Infective process. Aseptic measures.

Chain of infection, Infective process. Aseptic measures.
Chain of infection.
What is the chain of infection?

        Whether or not an infection happens will depend on a number of things. It is best explained by looking at the ‘chain of infection’ which consists of six ‘links’ that have to be present for an infection to happen. The links are:

  1. Pathogen: Microorganism that causes disease.
  2. Reservoir: Where the pathogen lives and grows usually in warm, moist, dark places. Examples – cut or open area, bladder, and lungs.
  3. Portal of exit: How pathogen leaves one place or host. Examples – drainage & secretions, urine, stool, blood, breathing, sneezing, or coughing.
  4. Transmission: How pathogen is carried from portal of exit to portal of entry. Examples – hands, food, mouth, and clothing.
  5. Portal of Entry: How pathogen enters new place or host. Examples – cuts, mucous membranes (eyes, nose, mouth).
  6. Susceptible Host: Someone more likely to become infected. Elderly people are more susceptible due to aging changes.

        You can stop the process by ‘breaking’ the chain and removing one of the links.

        Some examples are:

  1. Reservoir: Keep cuts, etc. clean and uncovered. Keep surroundings clean.
  2. Portal of exit: Cover mouth and nose when coughing or sneezing. Cover open areas if draining.
  3. Transmission: Wash hands. Keep clothing clean by holding things away from you. Wear gloves, mask, and apron when needed.

        By doing these things, you may stop an infection either to you or your care.

Infective process.

Modes and control of transmission

        There are six common modes of transmission of infection. (See Table) If the mode of transmission is known, precautions can be put in place to prevent outbreaks. Precautions will vary according to the microorganism involved and the context of the case. For instance a case of influenza in a normal household setting does not require strict precautions, where as one in a long term care home might. In hospitals, the infection control team can be a source of advice on which precautions to use. Outside hospitals, the local public health authority can be consulted.

         Modes of transmission of infections and corresponding ways of controlling spread. Note that the precautions to be taken vary with the microorganism and the context of the illness.

ContactDirectDirect physical contact (body surface to body surface) between infected individual and susceptible host.Examples: Influenza virus; Infectious mononucleosis; chlamydia.Precautions: Hand hygiene; masks; condoms.
IndirectInfectious agent deposited onto an object or surface (fomite) and survives long enough to transfer to another person who subsequently touches the object.Examples: RSV; Norwalk; rhinovirus; perhaps influenza.Precautions: Sterilizing instruments; disinfecting surfaces and toys in school.
DropletVia coughing or sneezing, or (in health care) during suctioning. Droplets are relatively large (>5 µm) and can be projected up to about one metre.Examples: Meningococcus; influenza (though there is some debate); respiratory viruses.Precautions: Masks; cover mouth; stand clear.
Non-contactAirborneTransmission via aerosols (airborne particles <5µm) that contain organisms in droplet nuclei or in dusts. Can be spread via ventilation systems.Examples: TB; measles; chickenpox; smallpox (and maybe influenza: controversial, as more likely via droplets).Precautions: Masks; negative pressure rooms in hospitals.
VehicleA single contaminated source spreads the infection (or poison). This can be a common source or a point source.Examplesa) Point source: Food-borne outbreak from infected batch of food; cases typically cluster around the site (such as a restaurant)b) Common source: The Listeriosis outbreak in Canada in 2008 was linked to a meat production facility in Ontario. It caused 20 cases across five provinces. Cases may be widely dispersed due to transport and distribution of the vehicle.Precautions: Normal safety and disinfection standards. Deliberate contamination of Tylenol in 1982 led to the use of tamper-proof containers for medicines.
Vector-borneTransmission by insect or animal vectors.Example: Mosquitoes – malaria vector, ticks – Lyme disease vector.Precautions: Protective barriers (window screens, bed nets); insect sprays; culling animals.
  • Immune response.

The human immune system has two levels of immunity: specific and non-specific immunity.    Through non-specific immunity, also called innate immunity, the human body protects itself against foreign material that is perceived to be harmful. Microbes as small as viruses and bacteria can be attacked.

Aseptic measures.

Principles of ‘clean’/medical asepsis.

        Medical asepsis (clean technique) all practices that reduce the dumber, growth, transfer and spread of pathogenic microorganisms. They include hand washing, bathing, cleaning environment, gloving, gowning, wearing mask, hair and shoe covers, disinfecting articles and use of antiseptics. You can prevent infection from spreading by providing clients with clean surroundings.

Principles of disinfection

        Disinfection: Process of eliminating pathogenic organisms on an inanimate object with the exception of spores. Disinfectant: Is a chemical substance that kill most of the bacteria is used for disinfecting only an inanimate object e.g. (phenol, chlorine).Those bacteria that not killed are slowed in their growth. Reusable plastic bedpans, trays, and equipment are sanitized (washed in bacterial cleanser), dries, and stored in clean bags.

        Antiseptic solution: Is a substance that is used on person’s skin to inhibit the growth and activity of microorganisms, but not necessarily destroy them. Contamination: The process by which something is rendered unclean or unsterile

        Concurrent disinfection; Practices that are done, on a day to day basis in the care of the patient, his lies, and his immediate environment to limit or control spread of microorganisms.

Principles of sterility/Principles of surgical asepsis

        Surgical asepsis (sterile technique); Practices that keep an area or objects free from all microorganisms nonpathogenic and pathogenic including spores and viruses. Sterilizing kills all bacteria. Unless bacteria are dead, an object is not sterile. A sterile object becomes contaminated when exposed to air or other objects. Diagnostic equipment and metal bedpans are most commonly sterilized by autoclaving (an intense heat process).


        One way to stop the spread of infection is by keeping the care recipient’s home clean. You can do this by following these guidelines:

  • Hold linens and other supplies away from your body.
  • Separate clean and dirty objects.
  • Keep things off the floor. Anything that falls on the floor is considered dirty and must be cleaned appropriately before using.

Cleaning and disinfecting – Keeping germs away:

        Another critical method for preventing the spread of germs is cleaning and disinfecting surfaces. Cleaning refers to washing with soap and water, and disinfecting refers to use of a cleaning product that kills bacteria and other germs. Disinfection is especially important in the kitchen and bathroom.

        Some general steps are involved in the proper cleaning and disinfection of surfaces:

  • Carefully follow directions and precautions on all cleaning products.
  • Begin by cleaning the surface thoroughly with soap and water or another cleaner.
  • After cleaning, if you need to use a disinfectant, apply it to the area and let it stand for a few minutes or longer following the directions on the product.
  • Wipe the surface with a paper towel that can be thrown away or a cloth that will be washed immediately afterward.
  • After cleaning or disinfecting, always wash hands, even if you wore gloves.