(A&E) (Clinical Imaging) (Infection)

Overview

• Respiratory infection characterized by inflammation of the alveolar space
• Bacterial pneumonia is most common (can also have viral and fungal). Streptococcus pneumoniae is the most common pathogen.
• CAP
  • Typical
    • Streptococcus Pneumoniae → most common. May have rusty sputum.
    • Haemophilus Influenzae → especially in COPD patients. Gram negative coccobacilli.
    • Staphylococcus Aureus → IVDU and also occurs after influenza. Causes cavitating lesions (gas filled lesions) on CXR. Gram positive cocci found in clusters.
    • Klebsiella Pneumoniae → alcoholics and diabetics. Causes cavitating lesions on CXR (typically upper lobe). Typically causes blood stained sputum (red-currant jelly appearance). Commonly due to aspiration. Commonly causes lung abscess formation and empyema.
  • Atypical
    • Mycoplasma Pneumoniae → associated with erythema multiforme (ring-shaped rash) and autoimmune haemolytic anaemia (cold agglutins, IgM). Dx with serology and positive cold agglutination test.
    • Legionella Pneumophilia → faulty air conditioning, recently returned from holiday. Causes hyponatraemia and abnormal LFTs. (Legionella = Low sodium and Liver derangement). Dx with urinary antigen.
    • Chlamydia Psittaci → pet birds
    • Pneumocystis Jirovecii → HIV (any immunosuppressed individual). Causes desaturation on exercise. Tx with co-trimoxazole (trimethoprim and sulfamethoxazole).
• HAP (>48 hrs after hospital admission). Tx with Tazocin.
  • Staphylococcus Aureus → IVDU. Causes cavitating lesions on CXR. (MRSA = tx with Vancomycin)
  • Pseudomonas Aeruginosa → CF and bronchiectasis.
• Majority of patients develop community-acquired pneumonia, however some patients within hospitals develop hospital-acquired pneumonia (arise >48 hrs after hospital admission)
• Risk Factors → old age, chronic diseases (COPD, HF, Bronchiectasis), Immunosuppression (HIV, DM), crowded living conditions
• Pneumonia Overview + Tx Flowchart

Aspiration Pneumonia ⇒ seen in patients with dysfunctional or unsafe swallow (stroke, myasthenia gravis, bulbar palsy, alcoholics). Most commonly affects the right lung as the right bronchus is wider and more vertical than the left, making it more likely to facilitate the passage of aspirate (ie. on CXR, consolidation would be at right lung base). Tx with amoxicillin + metranidazole.

Making Diagnosis

Clinical Features:

(Typical Pneumonia)

• Productive cough with purulent sputum (yellow-greenish)
• High fever and chills
• Pleuritic chest pain