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    Community Acquired Pneumonia (Adult) – Diagnosis

    Infections, Respiratory

    Last Reviewed on Aug 25, 2020
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    • 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?


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


    Related Information

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