Infection Concept Review Flashcards

Concept Overview and Definitions

  • Infection: Defined as the invasion of body tissue by microorganisms (pathogens) with the potential to cause illness or disease.
  • Temporal Trajectory:
    • Acute Infection: Characterized by a rapid onset, severe symptoms, and a short duration.
    • Chronic Infection: Characterized by a prolonged duration, persisting for months or years, often with insidious onset.
  • Extent of Systemic Involvement:
    • Localized Infection: Confined to a specific, limited area of the body.
    • Systemic Infection: Spreads throughout the entire body or affects multiple body systems (e.g., sepsis).
  • Epidemiological Scope:
    • Epidemic: An outbreak of disease that spreads rapidly and affects many individuals within a given population, community, or region simultaneously.
    • Pandemic: An epidemic that has spread across multiple countries, continents, or worldwide, affecting a substantial portion of the population.

Scope of Infection

Infections are systematically categorized across multiple dimensions:

  • Mode of Transmission: Direct, indirect, vehicle-borne, vector-borne, airborne.
  • Trajectory of Illness: Acute vs. chronic progression.
  • Body Systems Affected: Respiratory, gastrointestinal, urinary, reproductive, neurological, cardiovascular, musculoskeletal, integumentary.
  • Classification of Causative Organism: Bacteria, viruses, fungi, parasites, prions.
  • Length of Transmission: Short-term exposure vs. prolonged/continuous transmission risks.
  • Closely Related Concept: Immunity (the host's structural and cellular defense mechanisms against foreign pathogens).

Normal Microbial Flora

Microorganisms normally reside as commensal or mutualistic flora across specific anatomical locations within the human body:

  • Skin: Primary external physical barrier hosting resident microbiota.
  • Nasal Passages: Mucosal surfaces of the upper respiratory tract.
  • Oropharynx: Posterior pharyngeal mucosa.
  • Mouth: Oral cavity, gingiva, and sublingual surfaces.
  • Intestine: Gastrointestinal lumen (colonizing both small and large intestines).
  • Anterior Urethra: Distal segment of the urinary tract.
  • Vagina: Vaginal mucosal epithelial surface.

The Chain of Infection

Transmission of infectious agents requires a complete, unbroken sequence of six interconnected links:

  • Infectious Agent / Microorganisms: The pathogen (bacteria, virus, fungus, parasite) capable of producing infection.
  • Reservoir: The natural habitat or environment where the pathogen lives, multiplies, and survives (e.g., humans, animals, environmental surfaces, water, soil).
  • Portal of Exit: The site through which the microorganism escapes from the reservoir.
    • Respiratory Tract: Mucus, sputum, droplets ejected via coughing or sneezing.
    • Gastrointestinal (GI) Tract: Saliva, emesis, feces.
    • Urinary Tract: Urine, urethral secretions.
    • Reproductive Tract: Vaginal secretions, semen.
    • Blood: Needlesticks, open wounds, blood transfusions.
    • Tissue: Exudate, skin lesions, drainage.
  • Mode of Transmission: The mechanism by which the pathogen travels from the reservoir to the host.
    • Direct Transmission: Direct physical contact between host and source (e.g., touching, kissing, sexual contact, direct droplet spray over short distances).
    • Indirect Transmission:
    • Vehicle-Borne: Inanimate objects (fomites), contaminated food, water, biological products, or surgical instruments carrying the pathogen.
    • Vector-Borne: Intermediate biological carriers (e.g., mosquitoes, ticks, fleas) or mechanical vectors.
    • Airborne: Transmitted via fine droplet nuclei or dust particles suspended in air currents over extended distances and times.
  • Portal of Entry: The route through which the pathogen enters a susceptible host (e.g., non-intact skin, mucous membranes, respiratory tract, GI tract, genitourinary tract).
  • Susceptible Host: An individual with impaired or insufficient immune defense mechanisms vulnerable to infection.

Disease Categorization and Microbial Characteristics

  • Communicable Disease: An infectious disease capable of being transmitted directly or indirectly from one individual, animal, or reservoir to a susceptible host.
  • Infectious Disease: A clinical manifestation of disease resulting from the presence and activity of pathogenic microbial agents.
  • Pathogenicity: The intrinsic ability of a microorganism to cause disease in a host.
  • Virulence: The degree or intensity of pathogenicity of a specific microorganism, determined by its invasion dynamics and toxin production.
  • Opportunism: The capacity of normally non-pathogenic organisms to cause disease when host immune defenses are compromised or normal flora is disrupted.

Healthcare-Associated Infections (HAIs) and Aseptic Techniques

  • Healthcare-Associated Infections (HAIs): Infections acquired by patients during the course of receiving healthcare treatment for other conditions within a healthcare facility.

    • Major Types: Central line-associated bloodstream infections (CLABSI), catheter-associated urinary tract infections (CAUTI), surgical site infections (SSI), ventilator-associated pneumonia (VAP).
    • Prevention Strategies: Rigorous hand hygiene, strict adherence to aseptic techniques, bundle care practices, routine environmental disinfection, antimicrobial stewardship, timely removal of invasive devices.

  • Asepsis: The state of being free from pathogenic microorganisms.

    • **Medical Asepsis (