Respiratory Tract Infections

• What types of pathogens are associated with respiratory tract infections?


  • Bacterial
  • Fungal
  • Viral
• Which virus is commonly associated with respiratory infections?

  Influenza
• What is the role of ciliated cells in the respiratory tract?


  They help to clear mucus and pathogens from the airways.
• Why do humans not succumb to respiratory infections more often despite inhaling many organisms daily?


  Due to effective host defense mechanisms.
• What are the physical host defense mechanisms in the respiratory tract?

  • Mucus
  • Ciliated columnar epithelium
  • Saliva
  • Hairs in anterior nares
  • Cough and epiglottic reflex
• What are the immunological host defense mechanisms in the respiratory tract?


  • Humoral and cell-mediated immunity
  • Cytokines
  • Antibodies
  • Polymorphonuclear leukocytes and monocytes
• What is the typical source of respiratory infections?

  Contact, droplets, aerosols, and fomites.
• What are the steps involved in laboratory diagnosis of respiratory infections?

  1. Assess clinical history and specimen suitability
  2. Collect appropriate sample
  3. Interpret culture significance
  4. Isolate and identify pathogens
  5. Conduct antimicrobial susceptibility testing
  6. Release report with findings
• What types of pathogens are associated with respiratory tract infections?


  • Bacterial
  • Fungal
  • Viral
• Which virus is commonly associated with respiratory infections?

  Influenza
• What is the role of ciliated cells in the respiratory tract?


  They help to remove microbes and debris from the respiratory tract.
• What is the average number of organisms a human can inhale in a day?


  Over 500,000 organisms
• What are the physical host defense mechanisms against respiratory infections?

  • Saliva
  • Hairs in anterior nares
  • Cough and epiglottic reflex
  • Ciliated cells in the respiratory tract
• What are the immunological host defense mechanisms against respiratory infections?


  • Humoral and cell-mediated immunity
  • Cytokines
  • Antibodies
  • Polymorphonuclear leukocytes and monocytes
• What is the significance of the alveolar lining fluid in respiratory defense?


  It contains specific and non-specific antimicrobial peptides.
• What are the common routes of respiratory pathogen transmission?


  • Infected contact
  • Droplets
  • Aerosols
  • Saliva/Nasal secretions
  • Hands
  • Mucous membranes
  • Fomites
• What are the steps involved in laboratory diagnosis of respiratory infections?

  1. Assess clinical history and suitability of specimen
  2. Collect appropriate sample to culture specimen
  3. Interpret significance of culture
  4. Isolate any pathogen(s)
  5. Identify pathogen(s)
  6. Antimicrobial susceptibility testing
  7. Release report with significance of pathogen and sensitivities
• What types of samples are collected for respiratory infections?

  Swab, BAL, pleural aspirate, bloods, lung biopsy, sputum
• Why must respiratory samples be processed in a microbiology safety cabinet?


  To ensure safety and prevent contamination.
• What are the common infections of the upper respiratory tract?

  • Pharyngitis/Tonsillitis
  • Rhinitis
  • Sinusitis
  • Laryngitis
  • Otitis media
• What are the typical symptoms of sinusitis?


  Fluid build-up, runny and stuffy nose, facial pain, headaches.
• How long do symptoms of sinusitis typically last?


  Up to 10 days
• What is the typical treatment for sinusitis?


  Self-care and pain relief; antibiotics are rarely given.
• What are the typical symptoms of laryngitis?


  Hoarse voice, sore throat, irritating cough.
• How long do symptoms of laryngitis typically last?


  1. 2 weeks
• What are the typical symptoms of otitis media?


  Ear pain, trouble hearing, drainage of fluid from the ear.
• What is the most frequent bacterial cause of pharyngitis?

  Streptococcus pyogenes
• What are the characteristics of Streptococcus pyogenes?


  • Non-motile Gram-positive cocci, arranged in chains
  • Fastidious facultative anaerobe
  • Known as β-haemolytic, Lancefield group A
  • Carriage rate of 15-20%
  • Susceptible to most antibiotics, with penicillin generally used
• What are the Lancefield groupings?


  • Serological analysis of specific carbohydrate (C) antigens within the cell wall of β-haemolytic Streptococci
  • Arranged in 20 groups: A-H and K-V
  • Most relevant groups: A, B, C, D, F, and G
• What is the principle behind the Lancefield assay?


  It uses antigen-antibody binding to identify specific Streptococcus groups.
• What are the virulence factors of Streptococcus pyogenes?


  • Pili
  • M protein
  • Hyaluronic acid capsule
  • Superantigens (SpeA, SpeC, SpeG)
  • DNases
  • Leukotoxins (SLO, SLS)
• What are the post-pharyngitis complications?


  • Scarlet Fever
  • Myocarditis
  • Sydenham’s chorea
  • Rheumatic fever
  • Subcutaneous nodules and erythema marginatum
• How does GAS infection lead to rheumatic heart disease?


  It stimulates immune responses that cause inflammation in the heart.
• What is the role of chemokines in neutrophil migration towards bacteria?


  Without chemokines, neutrophils will not migrate towards bacteria.
• What is the significance of the capsule in Streptococcus pyogenes?


  It repels opsonin binding, aiding in evasion of the immune response.
• What is the effect of DNase on neutrophil extracellular traps (NET)?


  DNase cleaves NET, aiding bacterial evasion of the immune response.
• What is the role of C5a peptidase in Streptococcus pyogenes?


  It cleaves chemokines, inhibiting neutrophil migration.
• What is the significance of mitral valvulitis in rheumatic heart disease?


  It involves inflammation due to GAS infection and immune response.
• What is the main focus of the study material provided?

  Respiratory Tract Infections
• Who is the author of the study material?

  Dr. Ryan Kean