NURS 216: Infection

Infection Basics

• What is Infection?

  • The entrance of harmful agents into the body.

  • These agents multiply and cause damage to tissues.

  • This process ultimately leads to signs of inflammation.

• Infection vs. Colonization

  • Infection: Involves the invasion of a host by a pathogen, leading to a host response characterized by inflammation.

  • Colonization: Refers to the presence of microorganisms in or on the body without causing signs of inflammation or disease.

• Factors Influencing Severity of Infection

  • Pathogen Factors:

    • Pathogenicity: The inherent ability of a pathogen to cause disease; refers to the severity of the pathogen itself.

    • Dose: The concentration or amount of the bacteria or pathogen present.

    • Virulence: The degree of pathogenicity, specifically how quickly a pathogen invades cells or its replication rate.

    • Portal of Entry: The specific entry site for the pathogen (e.g., cuts, skin breaks, ingestion).

      • The airway is highlighted as the most significant portal of entry.

  • Host Factors:

    • Susceptibility: The fragility of the host or their inability to effectively protect themselves against the pathogen.

    • Barriers: The body's natural lines of defense (e.g., skin, mucous membranes).

    • Immunity: The host's immune status and ability to mount a defense.

    • Comorbidities: Existing health conditions that can weaken the host or increase susceptibility.

The Chain of Infection

• The Chain of Infection describes the sequential process required for an infection to occur and spread.

• Links in the Chain and How to Break Them:

  1. Infectious Agent: The pathogen (e.g., bacteria, virus, fungus, parasite).

     • Break the Chain: Sterilization, antimicrobial stewardship (appropriate use of antimicrobials).

  2. Reservoir: The place where a pathogen can live, grow, and flourish.

     • Types of Reservoirs:

       • Animal: Infected animals.

       • Human:

         • Asymptomatic: Carriers who show no symptoms but can transmit the pathogen.

         • Symptomatic: Individuals showing signs of illness.

       • Non-living Reservoirs: Soil, water, contaminated surfaces.

     • Break the Chain: Vaccination, better nutrition, glycemic control (for certain host situations).

  3. Portal of Exit: The pathway by which a pathogen leaves the reservoir.

     • Examples: Gastrointestinal tract, genitourinary tract (mostly genital secretions), respiratory tract (coughing, sneezing), skin (open wounds), mucous membranes, blood.

     • Break the Chain: Cough etiquette, wound coverage.

  4. Mode of Transmission: The method by which a pathogen is transferred from the reservoir to a susceptible host.

     • Types of Transmission:

       • Contact Transmission:

         • Direct Contact: Skin-to-skin touch (e.g., touching, kissing).

         • Indirect Contact (Fomite): Contact with contaminated surfaces or objects.

         • Enteric Contact: Fecal-oral route.

       • Droplet Transmission: Occurs via large respiratory droplets expelled during coughing, sneezing, or talking.

         • Example: Influenza.

       • Airborne Transmission: Involves small aerosol particles that can remain suspended in the air for longer periods and travel further.

         • Example: Tuberculosis.

       • Vehicle-borne Transmission: A pathogen carried by a shared medium.

         • Examples: Contaminated food (e.g., Salmonella), contaminated water, blood, IV fluids, medications.

       • Vector-borne Transmission: Transmission via arthropods (like mosquitoes).

         • Biological Vectors: The pathogen multiplies or develops within the vector (e.g., malaria in mosquitoes).

         • Mechanical Vectors: The vector carries the pathogen on its body without being infected (e.g., flies carrying bacteria on their legs).

     • Break the Chain: Hand hygiene, masking, isolation, environmental cleaning (for specific pathogens like influenza).

  5. Portal of Entry: The site where the pathogen enters the susceptible host.

     • Examples: Skin and mucous membranes, respiratory tract, gastrointestinal tract, genitourinary tract, blood.

     • Break the Chain: Aseptic technique, proper device/line care.

  6. Susceptible Host: An individual who lacks effective resistance to a particular pathogen.

     • Break the Chain: Vaccination, adequate nutrition, glycemic control.

Stages of Infection

• The progression of an infection typically follows four stages:

  1. Incubation Period:

     • The time from exposure to the first appearance of symptoms.

     • No specific signs are evident yet.

     • For many pathogens, the patient can be contagious during this stage.

  2. Prodromal Period:

     • Characterized by vague, nonspecific symptoms.

     • Examples: Malaise (general discomfort), low-grade fever, mild myalgias (muscle aches).

  3. Acute Period (Illness):

     • The pathogen activity peaks.

     • Presents with localized signs at the infection site plus systemic responses.

     • Systemic responses include fever, tachycardia (rapid heart rate).

  4. Recovery Period (Convalescence):

     • Symptoms begin to resolve.

     • Energy levels return.

     • There is a risk of secondary issues, especially if the patient became deconditioned during the illness.

Local vs. Systemic Infection

• Local Infection:

  • Confined to a specific area of the body.

  • Symptoms are localized:

    • Redness

    • Swelling

• Systemic Infection:

  • Spreads throughout the body, often via the bloodstream.

  • Symptoms are systemic:

    • Fever

    • Rapid heart rate

    • Fatigue

Evasion of Host Defenses

• Pathogens employ various strategies to evade the host's immune system:

  • Presence of a Capsule: A protective outer layer that helps pathogens resist phagocytosis.

  • Building Proteins: Pathogens can produce proteins that interfere with immune responses.

  • Altering Organism's Antigenicity: Changing surface antigens to avoid recognition by immune cells.

  • Avoiding Contact with Defenses: Mechanisms to prevent interaction with immune cells.

  • Inhibiting Engulfment by Phagocytes: Preventing immune cells (phagocytes) from engulfing and destroying them.

  • Surviving Inside Phagocytes: Some pathogens can survive and even multiply within phagocytic cells.

  • Producing Toxins to Damage Defenses: Secreting substances that directly harm immune cells or inhibit their function.

Invasion of Cell Membranes

• Invasins: Enzymes produced by pathogens that destroy host cells and disrupt physical barriers.

  • Example: Hyaluronidase, an enzyme that breaks down hyaluronic acid (a component of connective tissue), allowing the pathogen to spread.

Nosocomial Infections

• Also known as healthcare-associated infections (HAIs).

• These are infections that occur in healthcare facilities.

• Examples:

  • Pneumonia

  • Urinary tract infections (UTIs)

  • Wound infections

Exemplar: Influenza (The Flu)

• Type of Virus: RNA virus.

• Major Types:

  • Type A: Most common type, responsible for major pandemics and epidemics.

  • Type B: Can be dangerous at times, especially in specific seasons.

  • Type C: Present but typically causes mild illness.

• Surface Proteins (Impact Virulence):

  • H (Hemagglutinin): Helps the virus attach to host cells.

  • N (Neuramindase): Helps the virus leave the host cell and spread to others.

• Transmission: Primarily by droplets and contact.

• Incubation Period: Typically $1-4$ days after exposure.

• Prominent Symptoms: Fever, chills.

Breaking the Chain of Influenza

• Specific interventions to prevent the spread of influenza:

  • Vaccination: Annual flu shots to build immunity.

  • Masking: Wearing masks to prevent droplet transmission.

  • Hand Hygiene: Frequent and thorough hand washing.

  • Isolation: Separating infected individuals to prevent spread.

  • Environmental Cleaning: Disinfecting surfaces to eliminate the virus.

References

• VanMeter, K. C., & Hubert, R. J. (2023). Gould's Pathophysiology for the Health Professions (7th ed.). Elsevier.