Healthcare Infection Control Quiz

Exanthematous Rashes

• Enterovirus infections can cause rashes
• Parvovirus B19 ("Slapped-cheek rash" or "Fifth disease") causes a rash
• Human Herpesvirus 6 (HHV-6) causes roseola infantum
• Measles is highly contagious, potentially leading to severe complications like pneumonia.
• Rubella can cause congenital rubella syndrome if a pregnant woman is infected

Viral Hemorrhagic Fever

• Ebola virus disease is a major source of outbreaks, predominantly in Africa.
• A recent West African outbreak involved ~30,000 cases.
• Hong Kong is at risk due to its global connections.
• Other causes include severe dengue, hantavirus hemorrhagic fever, yellow fever, Lassa fever, Crimean Congo hemorrhagic fever, and Marburg virus.

Viral-Associated Cancers

• Nasopharyngeal carcinoma is associated with Epstein-Barr virus (EBV).
• Hepatocellular carcinoma is linked to Hepatitis B virus (HBV) and Hepatitis C virus (HCV).
• Cervical cancer, anal cancer, and oropharyngeal cancer are associated with Human papillomavirus (HPV), particularly high-risk genotypes.
• Vaccines are available for HBV and HPV high-risk genotypes.
• Drug treatments exist for HBV and HCV.

Other Medically Important Viruses

• Monkeypox is a poxvirus primarily affecting rodents in West/Central Africa.
• A large international outbreak occurred in 2022, primarily impacting men who have sex with men (MSM) communities.

Arboviruses

• Arboviruses are transmitted by insects
• Japanese encephalitis and dengue are two primary arboviruses in Hong Kong.
• Other significant arboviruses include Zika virus, West Nile virus, and Yellow Fever virus.
• Dengue virus causes a clinical course with viraemia and possible shock, haemorrhage, or dengue fever. Clinical diagnoses include virus isolation, molecular techniques, and the dengue antigen capture ELISA.

Immune System Introduction

• Immunity is a defensive mechanism against diseases
• Antigens (infectious microbes or large molecules) trigger immune responses.
• Pathogens are antigens that break through the immune system.
• Different pathogens can be located in the body's cytosol, intracellular locations, or extracellular spaces.

Innate Immunity

• Innate immunity is fast, but limited in strength and specificity.
• Macrophages and NK cells are part of this type of immunity.

Adaptive Immunity

• Adaptive immunity is slower but stronger and specific to antigens, and has memory.
• B and T lymphocytes are part of adaptive immunity.

Secondary Immune Response

• The secondary immune response has a shorter lag time and higher antibody production.
• Strong memory from past exposure or immunization helps in this.
• Somatic hypermutation is a key process for generating antibody diversity.

Immune Responses to Infections

• Immune responses depend on the type of pathogen (extracellular or intracellular).
• Humoral responses involve B cells.
• Cell-mediated responses involve T cells.

Humoral Response

• Non-specific responses include the complement pathway, interferons, and acute-phase proteins.
• Specific responses rely on antibodies from B cells.
• Neutralisation, opsonization, and complement-mediated lysis are key functions of antibodies.

Cell-Mediated Immunity

• Non-specific responses include phagocytes and natural killer (NK) cells.
• Specific responses include cytotoxic T cells (Tc) and helper T cells (TH).
• Cytotoxic T cells kill infected cells, while helper T cells help other immune cells function.
• Distinct subtypes of TH cells each play different roles in the immune response like TH1, TH2, and TH17.

HIV Infection of CD4+ T Cells

• HIV infection depletes CD4+ T cells over time, progressing through stages from seroconversion to symptomatic disease and finally AIDS.

Phagocytes

• Phagocytosis involves chemotaxis (directed movement), attachment and uptake of microbes, and destruction by lysosomes.
• Macrophages and Granulocytes are two types of phagocytes.

Effector Mechanisms for Phagocytes

• Reactive oxygen intermediates (ROIs), reactive nitrogen intermediates (RNIs), and cytokines are employed for microorganism killing.
• T-dependent macrophages are activated by T cells. Interferons (e.g., IFN-γ) play a significant role in macrophage activation.

Mucosal Immunity

• Mucous is a key first line of defense against pathogens entering through the respiratory tract.
• Antigens are picked up by M cells and presented to dendritic cells in lymphoid follicles, leading to IgA-producing plasma cell activation and differentiation
• IgA is a critical antibody type in mucosal immunity.

Immunodeficiency

• Primary immunodeficiency is typically genetic.
• Secondary immunodeficiency is acquired.
• Consequences include recurrent infections and opportunistic infections.
• Genetic mutations and infections (e.g., HIV) can lead to immunodeficiency.

Anti-Tumor Immunity

• Tumor pathogenesis involves genetic mutations, viral-induced mechanisms, and other factors.
• Immunosurveillance and immune cells infiltrating tumors provide evidence of anti-tumor immunity.

Immune Checkpoints

• Immune checkpoint inhibitors can block PD-1 and PD-L1, allowing T cells to kill tumor cells more effectively.

Innate Immunity Defense Mechanisms

• Anatomical barriers prevent entry of pathogens (e.g., skin, mucosa).
• Chemical mediators (e.g., lysozyme, defensin) inhibit pathogen growth.
• Cellular components (e.g., macrophages, neutrophils) destroy pathogens

Humoral Immune Response

• Major components involved include antibodies (immunoglobulins), complement pathway, and interferons.
• Antibodies target, neutralise, and activate complement to destroy pathogens.

Cell-Mediated Immunological Response

• Involves T-lymphocytes.
• Cell-mediated cytotoxicity targets infected cells directly
• Cytokines from helper T cells help other immune cells function.

Burnet's Clonal Selection Theory

• The theory describes how different antigen-specific immune cells are selected and respond to antigens by proliferating.
• Primary and Secondary Responses are distinct phases of the immunological response.

Immunological Memory

• Primary and secondary responses differ in time of induction, reaction magnitude, and decline after the reaction phase.
• Immunological memory gives a faster and stronger response upon subsequent exposure to the same antigen.

Self and Non-Self Discrimination

• The adaptive immunity has unique mechanisms to prevent self-attack.
• Central tolerance and peripheral tolerance are important for immune-system self-regulation.

Acute Inflammation

• Inflammation is a physiological tissue response to injury caused by ischemia, physical injury, chemical agents, or infections.
• The cardinal signs of acute inflammation are redness, swelling, warmth, pain, and loss of function.
• Chemical mediators, blood vessels, and neutrophils are involved in the process.

Chronic Inflammation

• Prolonged inflammation (weeks or months) with tissue destruction and healing efforts.
• Occurs after unresolved acute inflammation or recurring inflammatory triggers.
• Histologic characteristics include mononuclear cell infiltrates, tissue destruction, fibrosis, and possible regeneration.
• Different chronic inflammatory types exist based on origin (e.g., post-infectious, hypersensitivity).

Antimicrobial Classification

• Classification of antimicrobials is based on structure, target mechanism of action, and activity (e.g., bactericidal, bacteriostatic).

Immunization

• Artificially inducing immunity to diseases.
• Vaccines induce active immunity by including weakened or killed pathogens, and it comes in varying forms (e.g., live-attenuated and inactivated).
• Passive immunity involves administration of pre-formed antibodies.

Infection Control

• Evidence-based procedures aim to prevent or reduce the risk of microbial transmission in healthcare settings (hospital-acquired infections).