Infection: community-acquired pneumonia (CAP)
Also refer to: Sputum culture test information
Brief description:
- One of the commonest infectious conditions leading to hospitalisation, although is commonly over-diagnosed.
- Streptococcus pneumoniae is the most important bacterial cause.
- In NZ Legionella is an important cause, particularly in spring and summer, with the commonest species being L. longbeachae (often associated with potting mix).
- Patients living in rest homes, including ‘hospital-level care’, should generally be managed as CAP, rather than hospital-acquired pneumonia.
Did you know?
- Determining the causative organism for CAP is usually not possible with any degree of certainty. This is because many of the organisms that can cause CAP are also normal inhabitants of the upper respiratory tract, so tend to grow in sputum samples regardless.
- Viruses are also likely an under recognised cause of CAP, however, again, differentiating between post-viral upper respiratory tract carriage and pneumonia is difficult.
Diagnostic approach & tests of choice:
- Patients not requiring admission to hospital generally do not require any microbiological testing other than for COVID-19.
- Exception: if patient would meet criteria for Oseltamivir, then influenza testing is recommended. If result will not be available in a timely fashion, it may be appropriate to start Oseltamivir and then stop if influenza PCR is negative.
- For adult patients requiring admission to hospital, these tests are recommended:
- 2 sets of blood cultures before antibiotics
- Nasopharyngeal swab for COVID-19 and influenza PCR
- Special situations:
- Strong exposure history for Legionella (e.g. potting mix) send sputum for Legionella PCR
- Radiological features of staphylococcal pneumonia (e.g. cavitation) send sputum for Gram stain and culture
- Farming/contaminated water exposures send blood samples for Leptospirosis serology and PCR
- Prolonged symptoms, or suspicious radiological features, send sputum for TB culture
- For adult patients with severe pneumonia requiring ICU admission, add these tests:
- Sputum (or other deep respiratory sample) for Gram stain and culture
- Sputum (or other deep respiratory sample) for Legionella PCR
Tests to avoid/specialist tests:
- Urinary pneumococcal antigen testing:
- We do not recommend this as a routine, as all empiric antibiotic regimens for CAP are targeted at S. pneumoniae anyway, and antigen testing does not provide a susceptibility result to allow antibiotic adjustment.
- Although it may be used as an antimicrobial stewardship tool to narrow the antibiotic spectrum away from other organisms, evidence suggests this actually occurs infrequently in clinical practise.
- Urinary Legionella antigen testing:
- This only detects Legionella pneumophila serotype 1, not L. longbeachae, which is the commonest species in NZ, so is not recommended.
- Sputum Gram stain and culture:
- Not recommended for the majority of patients with CAP (other than indications above), as is heavily contaminated by upper respiratory tract organisms, and can be misleading as to the causative organism.