Causes and Types of Pneumonia

Question 1

What are the causes of bacterial CAP?

Answer 1

• Streptococcus pneumoniae
• H. influenzae
• Legionella pneumophila
• Mycoplasma pneumoniae
• Clamydophila pneumoniae
• Moraxella catarrhalis - COPD, CRD

Question 2

What is a common cause of HAP?

Answer 2

Gram negative bacilli

Question 3

Describe S pneumoniae

Answer 3

• Most common pathogen, especially post influenza
• More common with splenic dysfunction
• Capsule that inhibits phagocytosis
• Pneumolysin - cytolytic toxin
• Culture and urine Ag
• Usually very sensitive to penicillin (20-25% macrolide resistance worldwide)

Question 4

What antibiotic is S pneumoniae usually v sensitive to?

Answer 4

Penicillin

Question 5

Describe viral pneumonia

Answer 5

• Together - second commonest cause of CAP after S. pneumoniae
• Influenza A&B cause 50% of cases

Question 6

Which viruses are more common causes of pneumonia in children?

Answer 6

RSV and parainfluenza (but RSV has higher mortality in adults)

Question 7

Which virus can lead to SARS (rare, epidemic strain)?

Answer 7

Coronavirus

Question 8

Which viruses more commonly lead to pneumonia in immunocompromised patients?

Answer 8

Adenovirus, HSV, VSV

Question 9

Describe S. aureus

Answer 9

• More common post influenza
• Common in IVDU - likely haematogenous spread (people injecting into femoral artery)
• Increased risk of rapidly progressing necrosis and cavitation
• Often associated GI Sx
• Has a variety of toxins → rarely develop toxic shock syndrome (superantigens the cause widespread T cell activation and cytokine release)
• Flucloxicillin (and maybe steroids for inflammatory response)
• Vancomycin, teicoplanin, fusidic acid
• Some cover with co-amoxiclav but otherwise not v good with broad spectrum

Question 10

Describe Legionnaire’s disease

Answer 10

• Contaminated water supply often seen in endemic outbreaks → cooling towers, humidifiers, portable water distribution (more likely in people coming back from travel e.g. Spain)
• Resist intracellular killing by alveolar macrophages unless activated by Th cells
• Neuro Sx - confusion, agitation, ataxia, lethargy
• GI Sx - watery diarrhoea, abdominal pain, nausea, vomiting
• Other systems → myocarditis/pericarditis, cellulitis, pancreatitis
• Pontiac fever - flu-like, self-limiting
• Worse with co-morbidities e.g. heart failure

Question 11

What are features of atypical pneumonia?

Answer 11

• More systemic Sx → myalgia, fatigue, headache, often non-productive cough
• CXR → often multipolar
• Mycoplasma pneumoniae, clamydophila pneumoniae

Question 12

Describe mycoplasma pneumoniae

Answer 12

• 4 yearly cycles
• Associated with hepatitis, autoimmune haemolysis, ITP, erythema multiforme, Stephen Johnson’s, transverse myelitis, bullous myringitis
• Long incubation

Question 13

Describe clamydophila pneumoniae

Answer 13

• 4 yearly cycles (not at same time as above)
• Biphasic → initial URTI, persistent hoarse voice and sinus disease more prevalent
• Outpatient treatment with doxycycline is sufficient

Question 14

Describe aspiration pneumonia

Answer 14

• Alcohol excess
• Dysphagia/GORD (gastro-oesophageal reflux)
• Seizures, altered mental status
• Altered swallow - MS, Parkinson’s
• Mechanical - NG tube, ETT, tracheostomy, OGD, bronchoscopy
• Cover anaerobes in addition to CAP, though recent studies suffuse similar aetiology to CAP or HAP depending on situation

Question 15

What might you see in a CXR in aspiration pneumonia?

Answer 15

Head slumped down (→ poor swallowing)

Question 16

Describe HAP

Answer 16

• Inhalation/aspiration/haematogenous
• More gram negative organisms/with resistant organisms
• Pseudomonas aeruginosa, klebsiella spp, E. Coli, acinetobacter, S. pneumoniae, H. influenzae
• Increased risk of drug resistance → multi-resistant pseudomonas, MRSA, VRE, CPO
• Broader spectrum antibiotics e.g. antipseudomonal penicillins, aminoglycosides, MRSA cover (vancomycin?)

Question 17

Which pathogens are likely to cause pneumonia in different types of immunocompromised hosts?

Answer 17

1) Neutrophil defect (post chemotherapy, AML - defect so can’t make neutrophils) → bacteria, filamentous fungi
2) Antibody defect (CLL, CVID) → encapsulated bacteria, respiratory viruses
3) T cell defect (HIV, HSCT) → (non-TB) mycobacteria, nocardia, pneumocystis
4) High dose steroids (CT disorders e.g RA) → pneumocystis, aspergillus

Question 18

Describe aspergillus as a cause of pneumonia

Answer 18

• Ubiquitous mould, inhaled (most common), always inhale but with normal immune system doesn’t cause problems
• Aspergillus fumigatus, niger
• Toxic metabolites that inhibit macrophage and neutrophil function
• Immunosuppressed, allowing haematogenous spread - especially after organ Tx, prolonged neutropenia
• Local invasion into the blood - bone marrow problems, T cell deficiency, transplant
• Rx → amphotericin, voriconazole, posaconazole, caspofungin

Question 19

Describe nocardia as a cause of pneumonia

Answer 19

• N. asteroides complex
• Often affects pt with T cell dysfunction
• Pneumonia with cavitation and abscesses, empyema or inflammatory endobronchial lesions
• Often concurrent non tender erythematous nodules that may drain purulent material (occ CNS)
• Get infected skin and nodules
• 6 months-year treatment (long term) with antibiotics

Question 20

Describe how HIV can cause pneumonia

Answer 20

• Increased risk of bacterial pneumonia, esp. S. pneumoniae
  Increased risk of infection with endemic mycoses, and more likely disseminated (reactivation of states esp. in southern states of USA)
• With low CD4 high risk of disseminated mycobacterium avium/intracellulare
• Cryptococcal pneumonia more likely to be symptomatic (bacteria more commonly causes meningitis)
• Lots of drugs now which worsen immune system

Question 21

Describe how PJP can cause pneumonia

Answer 21

• Pneumocystis jirovecii (fungus)
• Often found in immunocompetent lungs without Sx
• Adheres to alveolar epithelium and increases leak → bilateral effusion
• Progressive SOB, fever, non-productive cough → desaturated on exertion
• Rx septrin (trimethoprim sulphamethoxazole) + high dose steroids if pO2 < 9.3 kPa (hypoxic)