Organisms

• CAP typical organisms:

  • Streptococcus pneumonia (most common)
  • Haemophilus influenzae
  • Moraxella catarrhalis
• CAP atypical organisms:

  • Mycoplasma pneumonia
  • Legionella pneumophila
  • Chlamydophila pneumonia
• Atypical organisms tend to have a more insidious, subacute onset. Combination of pulmonary and extrapulmonary symptoms.
• HAP typical organisms:

  • Gram-negative bacilli (e.g. Pseudomonas aeruginosa)
  • Staphylococcus aureus
  • Legionella pneumophilia
• Immunocompromised patients:

  • At risk of infective organisms not usually seen in other patient groups
  • Bacterial - typical organisms as well as mycobacterium and non-tuberculosis mycobacterium
  • Fungal pathogens- aspergillus fumigatus and pneumocystis jirovecii
  • Viral pathogens - varicella zoster virus and cytomegalovirus
  • Parasitic pathogens - seen almost exclusively in immunocompromised patients
• Streptococcus pneumoniae:

  • Gram-positive alpha-haemolytic streptococci
  • Most common cause of CAP
  • Frequently causes a significant leucocytosis and a raised CRP
  • Classically gives rust coloured sputum
  • Diagnosed via urinary antigen tests
• Mycoplasma pneumoniae:

  • Rod-shaped bacterium that lacks a cell wall
  • Tends to affect a younger demographic
  • Causes a pneumonia with a prolonged, insidious onset that may exhibit extrapulmonary features: erythema multiforme, arthralgia, pericarditis and haemolytic anaemia
  • Diagnosis made by serology/ PCR (sputum sample)
• Legionella pneumophilia:

  • Gram-negative coccobacillus that causes atypical CAP
  • Encountered in those exposed to contaminated cooling systems, humidifiers and showers
  • Chest symptoms may be preceded by several days of myalgia, headache and fever
  • Hyponatraemia secondary to SIADH is a classical finding
  • Diagnosis is via urinary antigen testing
• Pseudomonas aeruginosa:

  • Typically causes HAP
  • In patients with bronchiectasis it may cause CAP
  • Often described as an opportunistic pathogen
  • Sputum is characteristically green
  • Bronchoalveolar lavage may be used to obtain samples
• Klebsiella pneumoniae:

  • Gram negative bacillus
  • Classically causes CAP in alcoholics
  • Sputum may have the characteristic red current jelly appearance
• Pneumocystis jirovecii:

  • Fungi
  • AIDS defining illness
  • Hypoxia and raised LDH are common findings
  • Diagnosed with sputum stains
  • Does not respond to antifungals
• Alcoholism is associated with klebsiella pneumoniae infection
• Exposure to birds is associated with Chlamydophila pneumoniae infection
• Hotel or cruise ship stay in the previous 2 weeks is associated with Legionella pneumophilia infection
• CAP = Streptococcus pneumoniae

  HAP = Pseudomonas aeruginosa
• Mycoplasma pneumonia can also cause abdominal pain and diarrhoea in young adults

  Causes a persistent dry and hacking cough