A 67 year old male, having presented with a presumptive diagnosis of Community Acquired Pneumonia (CAP) remains intubated and in need of mechanical ventilation at Day 5 of his admission to hospital.

  • Outline the factors that may affect the expected rate of resolution of their CAP
  • Outline your approach, and indication for, the diagnostic evaluation of non-resolving pneumonia
 

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College Answer

a) Host factors

Alcoholism, older age, and the presence of comorbid diseases such as diabetes and chronic obstructive lung disease. In addition, disorders of immune function, particularly AIDS and syndromes associated with deficient humoral immunity, can be associated with delayed resolution of pneumonia.

Severity of CAP Pathogen:

In general, resolution is more rapid with Mycoplasma pneumoniae, non-bacteremic Streptococcus pneumoniae, Chlamydophila (formerly Chlamydia) species, and Moraxella catarrhalis than with other organisms

(note to Examiners – don’t need to list all of these, just indicate that some organisms associated with rapid resolution, and which some of those organism are)

Unusual pathogen:

Such as: Mycobacterium tuberculosis, Nocardia, Actinomyces israelii, Aspergillus, Coxiella burnetii (Q fever), Chlamydia psittaci (psittacosis), Leptospira interrogans (leptospirosis), Pseudomonas pseudomallei (melioidosis)

Antibiotic Resistance

Development of complications from initial CAP

The two main forms of sequestered focus preventing adequate resolution of pneumonia are empyema and lung abscess.

Non-infectious aetiology to initial CAP and/or underlying lung disease

Respiratory Malignancy, lymphoma, Granulomatosis with polyangiitis (Wegener's), Diffuse alveolar hemorrhage, Bronchiolitis obliterans-organizing pneumonia (BOOP), Acute or Chronic eosinophilic pneumonia, Acute interstitial pneumonia, Pulmonary alveolar proteinosis, Sarcoidosis, Systemic lupus erythematosus, Heart failure, Pulmonary embolism

b)

Chest CT to look for sequestered areas of infection or for findings that suggest an alternative diagnosis.

Fiberoptic bronchoscopy patients – lesions, mechanicals respiratory lesion, unusual pathogen

Thoracoscopic or open lung biopsy

Discussion

Outline the factors that may affect the expected rate of resolution of their CAP

This is a question regarding a community-acquired pneumonia which meets with treatment failure.

There is a good article about that. It lists the following factors, which were identified as predictors of poor response to antibiotics:

  • Elderly patient
  • Multiple comorbidities
  • Alcoholism
  • Smoking (and COPD)
  • Multilobar pneumonia
  • Bacteraemia
  • Empyema and lung abscess
  • Legionella pneumonia
  • Polymicrobial pneumonia

However, the college goes even further. They list pathogens which are expected to resolve rapidly:

  • Strep pneumoniae
  • Moraxella catarrhalis
  • Chlamidophyla
  • Mycoplasma pneumoniae

They then list pathogens which are expected to respond poorly to antibiotic therapy:

  • Mycobacterium tuberculosis
  • Nocardia
  • Actinomyces israelii
  • Aspergillus
  • Coxiella burnetii (Q fever)
  • Chlamydia psittaci (psittacosis)
  • Leptospira interrogans (leptospirosis)
  • Pseudomonas pseudomallei (melioidosis)

They then mention offhand that a list of pathogens of this magnitude was not expected from the candidates.

Then, they cheat.

The discussion turns to non-infectious aetiology for the respiratory failure, which is somewhat unfair (as the candidates would have been focussing on pneumonia). However, the savvy graduate would have noticed the sneaky word "presumptive" in the question text. This patient does not have a confirmed diagnosis. So, their respiratory failure could be totally non-infectious. The following differentials are suggested:

  • Vasculitis (eg. Wegeners)
  • Malignancy (eg. lung primary, mets or lymphoma)
  • Alveolar haemorrhage
  • BOOP
  • Alveolar proteinosis
  • SLE
  • Heart failure
  • PE
  • Sarcoidosis
  • Eosinophilic pneumonia

This is a broad list, and the key message is that one should read the question carefully.

Outline your approach, and indication for, the diagnostic evaluation of non-resolving pneumonia

A list of investigations can be generated.

  • High-resolution CT
  • Bronchoalveolar lavage, with culture, gram stain, PCR for atypical bacterial fungal and viral pathogens
  • Serology for atypical bacterial fungal and viral pathogens
  • Investigations for immune compromise, including HIV serology and blood film to consider hematological malignancy
  • Bronchoscopy for sampling
  • Lung biopsy if other diagnostic modalities fail to yield an answer

References