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Pneumonia

Background knowledge ๐Ÿง 

Definition

  • An inflammatory condition of the lung affecting primarily the alveoli, usually caused by infection
  • Pneumonia differs from a lower respiratory tract infection (LRTI) in that there is consolidation seen on chest radiograph

Aetiology and clues

  • Bacterial
    • Streptococcus pneumoniae (may be preceded by viral infection) โ†’ rusty colour sputum, associated HSV reactivation common
    • Haemophilus influenzae (often comorbidities such as COPD, smoking, immunocompromise)
    • Staphylococcus aureus (IVDU, occurs after influenza)
    • Klebsiella pneumoniae (alcoholism, COPD, diabetes) โ†’ red currant jelly colour sputum
  • Atypical โ†’ headache, malaise, myalgia, rash, diarrhoea
    • Mycoplasma pneumoniae (young patients)
    • Legionella pneumophila (exposure to travel/air conditioning) โ†’ prominent GI symptoms, SIADH
    • Chlamydia pneumoniae (bird exposure)
    • Coxiella burnetii (farmyard animal exposure)
  • Mycobacterial
    • Tuberculosis โ†’ upper lobe consolidation/cavitation
  • Viral โ†’ pneumonitis, coryza
    • Influenza
    • Respiratory syncytial virus (RSV)
    • Parainfluenza
  • Fungal
    • Pneumocystis jirovecii (immunocompromised) โ†’ exertional dyspnoea/hypoxaemia
    • Histoplasma
    • Aspergillus

Clinical Features ๐ŸŒก๏ธ

Symptoms

  • Fevers
  • Cough (with or without sputum production)
  • Breathlessness
  • Chest pain (pleuritic in nature)

Signs

  • Tachypnoea and tachycardia
  • Fever
  • Dullness to percussion
  • Coarse crepitations on auscultation
  • Bronchial breathing

Investigations ๐Ÿงช

Investigations

  • Chest X-ray: consolidation, air bronchograms, alveolar opacities
  • Blood tests
    • Full blood count: leucocytosis or leucopenia
    • Inflammatory markers: raised CRP
    • Consider serology for: HIV, Mycoplasma, Coxiella
  • Blood cultures: identify causative organism in bacteraemic cases
  • Sputum Gram stain and culture: detect causative bacteria
  • Urine antigen tests (legionella, pneumococcal)

Management ๐Ÿฅผ

Supportive care

  • Oxygen (aim saturations 92-96%)
  • Invasive ventilation may be required in severe hypoxaemia
  • Hydration
  • Antipyretics

Definitive management

  • Antibiotics
    • Usual bacterial cover: e.g. amoxicillin, co-amoxiclav, benzylpenicillin, ceftriaxone, doxycycline, levofloxacin
    • Atypical bacterial cover: e.g. clarithromycin, azithromycin, doxycycline, levofloxacin
  • Antivirals: in cases of viral pneumonia (e.g. oseltamivir for influenza)

Complications

  • Pleural effusion: accumulation of fluid in the pleural space
  • Empyema: pus in the pleural space
  • Abscess formation: localised collection of pus within the lung
  • Respiratory failure: insufficient gas exchange due to alveolar involvement
  • Septicaemia: spread of infection to the bloodstream

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