Chapter 25: Asepsis and Infection Control

Components of the Infection Cycle

The infection cycle describes the sequence of events that allows infectious diseases to spread. Understanding each component is essential for effective infection control.

• Infectious Agent: Microorganisms such as bacteria, viruses, and fungi that can cause disease.

• Reservoir: The natural habitat where the organism lives and multiplies (e.g., humans, animals, soil, water).

• Portal of Exit: The path by which the organism leaves the reservoir (e.g., respiratory tract, blood, skin).

• Means of Transmission: How the organism is transferred (direct contact, indirect contact, airborne, vector, fomite, droplet).

• Portal of Entry: The route through which the organism enters a new host (e.g., mucous membranes, skin breaks).

• Susceptible Host: An individual who lacks effective resistance to the invading organism.

The Infection Cycle

Interrupting any link in the infection cycle can prevent the spread of infection. Effective infection control strategies target these links.

Infectious Agents

Different types of microorganisms can cause infections, each with unique characteristics.

• Bacteria: Most significant and prevalent in healthcare settings; can be classified by shape, Gram stain reaction, and oxygen requirements.

• Viruses: The smallest microorganisms; cause diseases such as the common cold; not responsive to antibiotics.

• Fungi: Plant-like organisms (molds and yeasts) found in air, soil, and water; can cause infections.

• Parasites: Organisms that live on or in a host, deriving nourishment at the host's expense.

Classification of Bacteria

Bacteria are classified based on several criteria:

• Shape:

  • Spherical (cocci)

  • Rod-shaped (bacilli)

  • Corkscrew-shaped (spirochetes)

• Gram Staining:

  • Gram-positive

  • Gram-negative

• Oxygen Requirement:

  • Aerobic (require oxygen)

  • Anaerobic (do not require oxygen)

Factors Affecting an Organism’s Potential to Produce Disease

• Number of organisms present

• Virulence (ability to cause disease)

• Competence of the host’s immune system

• Length and intimacy of contact between host and microorganism

Identification of Infectious Agents

• Endemic: Disease occurs predictably in a specific region or population.

• Pandemic: Global outbreak of a new or previously unidentified virus.

Possible Reservoirs for Microorganisms

• Other people

• Animals

• Soil

• Food, water, milk

• Inanimate objects

Common Portals of Exit

• Respiratory tract

• Gastrointestinal tract

• Genitourinary tract

• Breaks in skin

• Blood and tissue

Means of Transmission

• Direct contact

• Indirect contact (via fomites)

• Vector (e.g., insects)

• Droplet

• Airborne

Stages of Infection

Infections progress through several stages, each with distinct characteristics:

• Incubation Period: Organisms grow and multiply; no symptoms yet.

• Prodromal Stage: Person is most infectious; early, vague symptoms appear.

• Full Stage of Illness: Specific signs and symptoms of disease are present.

• Convalescent Period: Recovery phase; symptoms subside.

Inflammatory Response

The inflammatory response is a protective mechanism that helps neutralize, control, or eliminate pathogens and initiates tissue repair.

• Vascular Phase: Vasodilation increases blood flow (redness, heat); increased vessel permeability leads to swelling, pain, and loss of function.

• Cellular Phase: White blood cells (especially neutrophils) ingest debris; tissue repair begins.

Immune Response

The immune response is the body's defense against foreign substances (antigens).

• Humoral Immunity: Production of antibodies in response to antigens.

• Cell-Mediated Immunity: Activation of lymphocytes that destroy or react with harmful cells.

Factors Affecting Risk for Infection

• Integrity of skin and mucous membranes

• Normal pH levels

• White blood cell count

• Age, sex, hereditary factors

• Immunization status

• Fatigue, climate, nutrition, general health

• Stress

• Use of invasive medical devices

Laboratory Data Indicating Infection

• Elevated white blood cell count (normal: 5,000–10,000/mm3)

• Increase in specific types of white blood cells

• Elevated erythrocyte sedimentation rate (ESR)

• Presence of pathogens in urine, blood, sputum, or draining cultures

Outcome Identification and Planning/Infection Control

• Practice effective hand hygiene and personal hygiene

• Recognize signs of infection

• Maintain adequate nutrition

• Dispose of soiled articles properly

• Use appropriate cleaning and disinfecting techniques

• Stay up to date with immunizations

• Practice stress-reduction techniques

Asepsis

Asepsis includes all activities to prevent infection or break the chain of infection.

• Medical Asepsis: Clean technique to reduce the number of pathogens (e.g., hand hygiene, wearing gloves).

• Surgical Asepsis: Sterile technique to keep areas free from microorganisms (e.g., inserting catheters or IVs).

Five Moments for Hand Hygiene (WHO)

• Before touching a patient

• Before a clean or aseptic procedure

• After a body fluid exposure risk

• After touching a patient

• After touching patient surroundings

Bacterial Flora

• Transient Flora: Loosely attached to skin; removed easily with handwashing.

• Resident Flora: Found in skin creases; requires friction and sometimes a brush to remove.

Health Care-Associated Infections (HAIs)

HAIs are infections acquired in healthcare settings. Seven targeted HAIs include:

• Catheter-associated urinary tract infection (CAUTI)

• Surgical site infection (SSI)

• Central-line–associated bloodstream infection (CLABSI)

• Hospital-onset methicillin-resistant Staphylococcus aureus (MRSA) infections

• Clostridioides difficile (C. diff) infections (CDIs)

Multidrug-Resistant Organisms (MDROs)

• Methicillin-Resistant Staphylococcus aureus (MRSA)

• Vancomycin-Intermediate/Resistant Staphylococcus aureus (VISA/VRSA)

• Vancomycin-Resistant Enterococci (VRE)

• Carbapenem-Resistant Enterobacteriaceae (CRE)

• Carbapenem-Resistant Acinetobacter baumannii (CRAB)

• Clostridioides difficile (CDI)

Factors Determining Use of Sterilization and Disinfection Methods

• Nature and number of organisms present

• Type and intended use of equipment

• Available means for sterilization/disinfection

• Time required for the process

Personal Protective Equipment (PPE) and Supplies

• Gloves

• Gowns

• Masks

• Protective eyewear

Standard Precautions

Standard precautions are used for all patients, regardless of infection status, and apply to blood, body fluids (except sweat), nonintact skin, and mucous membranes. They include respiratory hygiene, safe injection practices, and mask use for high-risk procedures.

Transmission-Based Precautions

These are used in addition to standard precautions for patients with known or suspected infections transmitted by airborne, droplet, or contact routes. PPE must be donned upon entering and removed upon leaving the patient’s room.

• Airborne precautions

• Droplet precautions

• Contact precautions

Patient Teaching for Medical Asepsis at Home

• Wash hands before preparing/eating food and after using the bathroom

• Cook foods to appropriate temperatures

• Clean hands, cutting boards, and utensils before/after handling raw meat

• Keep food refrigerated

• Wash raw fruits and vegetables

• Use pasteurized milk and juices

• Use individual care items

Evaluating Patient Goals

• Correctly use medical asepsis techniques

• Identify health habits that promote health

• Recognize signs and symptoms of infection

• Identify unsafe situations in the home environment

Selected Questions and Answers

Additional info: This summary integrates foundational microbiology concepts with practical infection control measures, as relevant to healthcare and public health settings.