HOS1-3 Principles of Infection Control; Standard Precautions; Hand Hygiene

Administrative Requirements and Module Overview

• Course and Speaker Information

  • Title: Principles of Infection Control

  • Speaker: Prof Margaret IP, Department of Microbiology, Faculty of Medicine, The Chinese University of Hong Kong (CUHK).

  • Course Code: MEDU 3890; Lecture Date: 1st June 2026.

• Basic Infection Control Module (BICM) Requirements

  • This module is a compulsory requirement for all healthcare students before entering clinical training in Hospital Authority (HA) areas.

  • Activities Included:

    1. Lectures.

    2. Online Multiple Choice Questions (MCQ).

    3. Practical and Assessments.

    4. Qualitative fit-test for N95 (or equivalent) respirators.

  • Consequences of Non-compliance:

    • Barred from entering clinical areas.

    • A $20\%$ deduction from the final Clinical Microbiology (MEDU 3330) exam score.

Fundamentals of Infectious Diseases and Infection Control

• Infectious Diseases:

  • Defined as diseases that are transmissible.

  • Caused by microorganisms including bacteria, viruses, fungi, parasites, and prions (proteins).

• Infection Control:

  • Comprises measures intended to stop the transmission of infectious diseases.

• Definitions: Source vs. Reservoir

  • Source: The thing, person, object, or substance from which an infectious agent passes immediately to a host.

  • Reservoir: Man, animal, plants, soil, or inanimate organic matter in which an infectious agent lives and multiplies.

The Chain of Infection

• Components of the Chain

  1. Infectious Agents: Bacteria, Viruses, Fungi, Parasites.

  2. Reservoir:

     • Human or animal.

     • Environment.

     • Inanimate objects (e.g., medical equipment).

  3. Portal of Exit: Ways germs leave the source/reservoir.

     • Respiratory droplets: Coughing, sneezing.

     • Excretion: Faeces.

     • Blood and body fluids.

  4. Mode of Transmission: Ways germs are passed on.

     • Contact (Person-to-person or via environment/equipment).

     • Droplets.

     • Airborne.

  5. Portal of Entry: Ways germs enter a new host.

     • Non-intact skin.

     • Mucous membranes.

     • Gastrointestinal (GI) tract.

     • Respiratory tract.

     • Catheters and tubes.

  6. Host:

     • Factors include being immunocompromised or the presence of invasive devices.

• Specific Examples of Germs and Diseases

  • Bacteria:

    • Streptococcus pyogenes: Skin and soft tissue infection (SSTI), pharyngitis.

    • Streptococcus pneumoniae: Pneumonia, meningitis.

    • Staphylococcus aureus: SSTI, bacteremia.

  • Viruses:

    • Influenza A & B / COVID-19: Influenza-like illness.

    • Norovirus: Gastroenteritis.

    • Hepatitis B Virus ($HBV$): Hepatitis.

  • Fungi:

    • Candida species: Oral thrush, napkin rash.

  • Parasite:

    • Plasmodium species: Malaria.

Factors Affecting the Chain of Infection

• Organism Factors: Microbial dose and virulence.

• Transmission Route: Contact, aerosol, insect vectors, etc.

• Host Factors: Immunity and the integrity of non-specific immune defenses (e.g., the skin).

Isolation Precautions: Two-Tier System

• Tier 1: Standard Precautions

  • Applies to ALL patients regardless of diagnosis or presumed infection status.

  • Reduces risk from both recognized and unrecognized sources of infection.

  • A combination of Universal Precautions and Body Substance Isolation (BSI).

  • Body Substance Isolation Scope: Covers blood, all body fluids (pleural, ascitic, joint fluid, etc.), all secretions and excretions except sweat (regardless of visible blood), non-intact skin, and mucous membranes.

  • Key Elements: Hand hygiene, PPE (gloves, mask, eye protection, gown), sharps precautions, decontamination of equipment/environment, linen and waste disposal, and immunization/prophylaxis.

• Tier 2: Transmission-Based Precautions

  • Additional precautions used when standard precautions alone are insufficient.

  • Applied based on the mode of transmission: Contact, Droplet, or Airborne.

  • Should be applied empirically based on symptoms (e.g., isolation for measles before diagnosis if rash and fever are present).

Hand Hygiene: The Primary Measure

• Importance: The most important measure to prevent the spread of infection; shown to decrease hospital-acquired infection (HAI) rates and $MRSA$ transmission rates.

• Alcohol Handrub (AHR) vs. Soap

  • Benefits of AHR: Requires less time, more effective for standard handwashing, more accessible than sinks, reduces bacterial counts, and improves skin condition due to glycerol.

  • When to use Soap and Water: Visibly dirty hands, before eating, after using toilets, and after caring for a person with diarrhea.

• Relative Efficacy (Mean Change in $log_{10}$ CFU)

  • Soap: $\approx 0.5$

  • Iodophor: $\approx 1.0\,to\,1.5$

  • $4\%$ Chlorhexidine Gluconate ($CHG$): $\approx 2.0\,to\,2.5$

  • $70\%$ Alcohol: $\approx 3.5$

• The Seven-Step Technique ($20\,seconds$)

  1. Palm to palm.

  2. Right palm over left dorsum with fingers interlaced (and vice-versa).

  3. Palm to palm with fingers interlaced.

  4. Back of fingers to opposing palm with fingers interlocked.

  5. Rotational rubbing of right thumb clasped in left palm (and vice-versa).

  6. Rotational rubbing of fingertips to opposing palm (and vice-versa).

  7. Rotational rubbing of wrists.

• Professional Standards (Extra Tips)

  • "Bare below elbow": No wrist jewelry or watches.

  • No stoned rings.

  • No artificial nails or nail varnish.

• WHO Five Moments of Hand Hygiene

  1. Before touching a patient.

  2. Before a clean/aseptic procedure.

  3. After body fluid exposure risk.

  4. After touching a patient.

  5. After touching patient surroundings.

Personal Protective Equipment (PPE)

• Gloves

  • Use before touching blood, body fluids, secretions, excretions, mucous membranes, or non-intact skin.

  • Change between dirty and clean sites on the same patient.

  • Remove promptly after use; do not wear between patients or outside the patient zone (e.g., canteen, elevator).

  • Note: Gloves do NOT replace hand hygiene. Hand hygiene must be performed before putting on and after removing gloves.

• Gowns

  • Made of impervious material; single-use only.

  • AAMI Level 1: Fluid repellent; used for general patient care.

  • AAMI Level 3: Fluid resistant; used for procedures where splashing is anticipated (e.g., resuscitation).

  • Surgical Gowns: Sterile, lint-free, highest fluid protection in critical zones.

• Masks and Respirators

  • Surgical Masks: Prevent droplet transmission; change when wet/soiled; do not reuse.

  • N95 Respirator: Non-oil resistant; filters at least $95\%$ of airborne particles (up to $0.3\,\mu m$); prevents airborne transmission; requires fit-testing.

• Eye Protection

  • Includes visors, face shields, and goggles to protect mucous membranes from splashes.

Specific Transmission-Based Precautions

• Contact Precautions

  • Microbes: Diarrheal pathogens (C. difficile, Salmonella, Campylobacter, Norovirus), antibiotic-resistant pathogens ($MRSA$, $VRE$, $CPE$), and Scabies.

  • Measures: Single room or cohort patients; single-use gown and gloves; dedicated or disinfected equipment.

• Droplet Precautions

  • Transmission: Large particles (> 5\,\mu m) transmitted via close contact (< 3\,feet).

  • Microbes: Influenza, COVID-19, Pertussis, Mumps, Rubella, Group A Streptococcus, Meningococcal infection.

  • Measures: Single room or cohort; wear surgical mask within $3\,feet$ of patient.

• Airborne Precautions

  • Transmission: Droplet nuclei (< 5\,\mu m) suspended in air over long distances.

  • Microbes: Tuberculosis ($TB$), Measles, Chickenpox.

  • Measures: Airborne Infection Isolation Room ($AIIR$) with negative pressure at $12\,ACH$ (air changes per hour), non-recirculating or HEPA-filtered air; wear fit-tested N95; care by immune staff for measles/chickenpox.

Practical Session: BICM Specifics

• Hand Wash Types

  • Social Hand Wash: Reduces > 80\% of microbial flora.

  • Antiseptic Hand Wash: Produces up to $3\,logs$ ($99.9\%$) reduction; uses antiseptic soap.

  • Surgical Scrub: Highest level of decontamination.

• PPE Donning and Doffing Habits

  • Gown: Tie at the side of the waist; overlap at the back. When doffing, fold from the inside and do not rip or shake the gown.

  • Surgical Mask: Water-repellent side (colored) faces out; malleable metal piece molded to nose bridge; upper strap at the crown, lower strap at the nape.

  • Shoe Covers: Regarded as providing only limited protection and not recommended in usual circumstances due to slip/fall risks.

• Assessment Standards

  • Hand Hygiene Assessment: Students apply $2\,mL$ of fluorescent cream. After washing with the 7-step method, hands are checked under UV light. Residual fluorescence indicates failure.

  • PPE Assessment: Students must demonstrate correct donning and doffing sequences (the "In and Out" poster) without recontamination.