INDEX

    Community Acquired Pneumonia (Adult) – Diagnosis

    Infections, Respiratory

    Last Updated Aug 25, 2020
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    Context

    • Community Acquired Pneumonia (CAP) = no prior hospitalization in past 14 days or onset <48 hours since admission.
    • In immunocompetent adults:
      • Typical bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus.
      • Atypical bacteria: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella species.
      • Viral: Influenza A/B, respiratory syncytial virus, adenovirus, parainfluenza, coronavirus (see Covid 19: Clinicians).

    Diagnostic Process

    • Clinical Manifestations
      • Dyspnea, tachypnea, cough +/- sputum changes, pleuritic pain.
      • Fever and/or rigors, malaise, muscle aches and confusion.
      • Abnormal lung exam (eg. crackles on auscultation or dullness to percussion).
    • Investigations
      • Chest radiographs:
        • New opacity, not suggestive of another diagnosis, confirms CAP.
      • FAST Ultrasound: B lines, hepatization.
      • Arterial blood gases: Consider if SpO2 <94%, receiving oxygen or otherwise severe CAP.
    • Severity Assessment
      • A prognosis clinical prediction rule, in addition to clinical judgement, is recommended. Two are commonly used:
      • Pneumonia Severity Index (PSI)
        • Useful tool which provides an excellent risk stratification. For most patients however, the CURB-65 is easier to use and requires fewer inputs.
      • CURB-65
        • Confusion, BUN > 7 mmol/L, RR > 30, SBP < 90 or DBP < 60 mmHg, Age > 65
    • Pathogen Identification
      • MRSA/Pseudomonas Risk:
        • Locally validated risk factors are best.
        • Risk factors include:
          • prior infection with MRSA or Pseudomonas or,
          • hospitalization involving IV antibiotics within the last 90 days.
      •  Sputum Testing:
        • Sputum Culture for patients admitted to hospital who can produce a sputum sample.
        • Sputum Gram Stain if severe CAP or if MRSA or Pseudomonas are suspected.
        • Obtain before starting antibiotics if possible.
      • Blood Culture:
        • Recommendations based on low quality evidence suggest only obtaining for severe CAP, or if MRSA or Pseudomonas are suspected.
        • Obtain before starting antibiotics if possible.
      • Urinary Antigen Testing:
        • pneumoniae – Consider for severe CAP.
        • Legionella – Obtain if there are risk factors (eg. travel) or ongoing outbreak. Consider for severe CAP.
      • Tests for Atypical Bacteria and Viruses (eg. Nasopharyngeal swab):
        • During flu season or an outbreak test for responsible pathogens.
    • Differential Diagnosis
      • Heart Failure.
      • COPD/Asthma exacerbation.
      • Aspiration pneumonitis.
      • Pulmonary embolism.
      • Acute Coronary Syndrome.
      • Pneumothorax.

    Quality Of Evidence?

    Justification

    Evidence relies on American Thoracic Society updated guidelines on CAP from 2019 as well as other sources all produced in the last few years.

    Moderate

    Related Information

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