infection control

Chain of Infection

  • The chain of infection is a sequence of factors needed for an infection to occur.
    • This sequence includes the following links:
    • Presence of an infectious agent
    • An available reservoir
    • A portal of exit from the reservoir
    • A mode of transmission from the reservoir to a host
    • A portal of entry to enter a susceptible host
    • A susceptible host
    • A break in any of the links can prevent the development of an infection.
    • The section will discuss each link of the chain of infection and how to break it.

Links in the Chain of Infection

1. Infectious Agent

  • An infectious agent is something that can cause disease, including:
    • Bacterium
    • Fungus
    • Virus
    • Parasite
    • Prion
  • Infectious agents can become dangerous in various ways:
    • Resident flora (non-pathogenic bacteria that live in the body) can cause infections when displaced to a different body location.
    • Example: Flora from the gastrointestinal tract moving to another part of the body.
    • To break this link, infectious pathogens must be destroyed through:
    • Disinfecting
    • Sterilizing and cleaning
    • Antimicrobial treatment (e.g., antibiotics, antifungals)

2. Reservoir

  • A reservoir is the habitat where the infectious agent lives, grows, and replicates.
    • Reservoirs can be:
    • Animate (e.g., humans, insects, birds, animals)
    • Inanimate (e.g., contaminated soil, water, food, medical equipment, IV fluids, feces)
  • Human reservoirs may not always show disease symptoms but can still transmit pathogens.
  • To break the chain of infection regarding reservoirs:
    • Nurses should practice proper hand hygiene when caring for clients.
    • Preoperative skin preparation must be performed before surgery.
    • Clean and disinfect clinical and surgical environments according to facility protocols.

3. Portal of Exit

  • A portal of exit is how an infectious pathogen leaves the reservoir.
    • Examples:
    • Body orifices (e.g., ears, nose, mouth, skin)
    • Blood or body fluids through the gastrointestinal or respiratory tract.
  • To break the chain at the portal of exit:
    • Implement careful containment of body fluids using drains or dressings.
    • Utilize methods to reduce body secretions.

4. Modes of Transmission

  • Transmission modes include:
    • Contact
    • Droplet
    • Airborne
    • Vehicle
    • Vector-borne
  • Hand hygiene and proper barrier devices can eliminate various modes of transmission.

5. Portal of Entry

  • A portal of entry is necessary for an infectious agent to enter a susceptible host.
    • It can also include any body orifice (e.g., ears, nose, mouth) or breaks in mucous membranes or skin.
    • Example: Influenza virus can enter and exit through the respiratory tract.
  • Invasive lines (e.g., catheters) also provide portals of entry.

6. Susceptible Host

  • A susceptible host is required for the infectious agent to take hold and potentially cause infection.
    • Not everyone exposed to an infectious agent becomes ill; some may be colonized without symptoms.
    • Factors that determine host susceptibility include:
    • Individual's immunity level at time of exposure.
    • Age, underlying diseases (e.g., HIV/AIDS, malignancies), and medications (e.g., immunosuppressants).
    • Surgical procedures, radiation therapy, and the use of indwelling devices (e.g., catheters).
  • To break this link, increase the host’s line of defense through:
    • Immunizations
    • Proper nutrition
    • Hygienic practices
    • Control of blood sugar levels

Factors That Increase Host Susceptibility

  • Age
  • Underlying Disease: Example: HIV/AIDS, malignancy
  • Medications: Immunosuppressants, antirejection medications, antineoplastics, antimicrobials, corticosteroids, gastric suppressants like proton pump inhibitors.
  • Surgical Procedures
  • Radiation Therapy
  • Indwelling Devices: Examples include endotracheal tubes, urinary catheters, central venous catheters, arterial catheters, and implants like pacemakers or artificial joints.

Modes of Transmission

Contact Transmission

  • Contact transmission occurs via:
    • Direct contact transmission: Micro-organisms move directly from an infected person to another.
    • Example: Client's blood contacting a nurse’s open abrasion.
    • Indirect contact transmission: Micro-organisms transferred via a contaminated object.
    • Example: Staphylococcus aureus spread through contaminated surfaces.
  • Personal Protective Equipment (PPE) should be used and changed between clients to prevent infectious agent transmission.

Droplet Transmission

  • Droplet transmission occurs when infectious droplets travel through the air and contact the mucosa of another person (e.g., sneezing, coughing).
  • Infectious droplets can spread pathogens such as:
    • Influenza virus
    • Bordetella pertussis
  • Client practices include:
    • Sneeze/cough into a disposable tissue.
    • Wearing surgical masks outside of their rooms.

Airborne Transmission

  • Airborne transmission occurs when small particulate matter remains suspended in the air and can be inhaled by others.
  • Clients with airborne conditions require negative pressure private rooms.
    • Examples of airborne infections include tuberculosis, rubeola (measles), and varicella (chickenpox).
  • Some droplet infections under specific conditions may also be airborne.

Vehicle and Vector-Borne Transmission

  • Vehicle transmission involves contaminated items transferring pathogens to multiple persons.
  • Vector-borne transmission involves organisms (e.g., mosquitoes, rats) carrying pathogens without being infected themselves.

Body Defenses Against Infections

1. Physical and Chemical Barriers

  • Skin is the largest organ and primary physical defense mechanism against pathogens.
    • Functions include:
      • Reducing loss of water
      • Protection against abrasion and microorganisms
      • Providing a semi-permeable barrier
    • Skin integrity is critical in fighting infections.
  • Mucous membranes secrete mucus to protect against invaders.
    • Humidification can be added to oxygen to keep membranes moist.

2. Nonspecific Immunity

  • Maintained by neutrophils and macrophages which destroy microorganisms through phagocytosis.

3. Specific Immunity

  • Involves antibodies (immunoglobulins) and lymphocytes.
  • Antibodies bind to antigens and activate immune responses.

Inflammatory Response

  • Activated during injury or presence of foreign bodies.

Steps of Inflammation

  1. Recognition of harmful stimuli.
  2. Activation of the inflammatory pathway.
  3. Release of inflammatory markers.
  4. Recruitment of inflammatory cells.
  • Triggers for inflammation can be infectious or noninfectious.
  • Manifestations of inflammation include heat, redness, swelling, pain, and loss of function.

Stages of Infection

  1. Incubation Stage: Time from exposure to the first symptom.
  2. Prodromal Stage: Initial non-specific symptoms develop as the infection replicates.
  3. Acute Illness Stage: Specific symptoms become obvious and the infection is severe.
  4. Period of Decline: Symptoms begin to subside and the host feels better.
  5. Period of Convalescence: The host returns to previous or new levels of health.

Types of Infection

  • Local Infection: Confined to one area; treated with topical and oral antibiotics.
  • Systemic Infection: A local infection that spreads, requiring intravenous antibiotics and monitoring.

Diagnostic Tests

  • Diagnostic tests assess diseases based on indications.
  • Examples include urinalysis for UTIs and blood tests for WBC counts to indicate infection severity.

Infection Control Measures

1. Hand Hygiene

  • Major source of transmission; practices include:
    • Using soap and water or alcohol-based sanitizers.
    • Hands should be washed for at least 15-30 seconds, approximately the length of two verses of “Happy Birthday.”

2. Medical Asepsis

  • Reduces the number of disease-causing organisms using isolation precautions.

3. Surgical Asepsis

  • Ensures sterile environments for surgical procedures; involves using sterile gloves and gowns.

4. Personal Protective Equipment (PPE)

  • Critical for protecting against transmission; includes gloves, masks, goggles, gowns, and face shields.

Multidrug-Resistant Infections (MDROs)

  • Infections caused by organisms resistant to multiple antimicrobials.
  • Examples include:
    • Methicillin-resistant Staphylococcus aureus (MRSA)
    • Vancomycin-resistant Enterococcus (VRE)
  • Precautions to prevent transmission include hand hygiene and contact precautions.

Healthcare-Associated Infections (HAIs)

  • Acquired in healthcare settings; four major types are:
    • CLABSIs, CAUTIs, SSIs, and VAPs.
  • Risk increased by indwelling devices and procedures performed in a high-risk environment.
  • Infection control bundles are utilized to minimize infection risks.

Needlestick Injury Prevention

  • Used needles should be immediately disposed of in designated containers to prevent injuries and contamination.