Infection: Legionella pneumonia; Legionnaire’s disease; Legionella infection
Brief description:
- Common cause of community acquired pneumonia (CAP), especially in spring/summer in NZ.
- Does not respond to beta-lactam antibiotics e.g. amoxicillin.
- Clinically and radiologically indistinguishable from other forms of CAP.
- Increased suspicion based on: time of year, potting mix exposure, lack of response to beta-lactams.
Did you know?
Does not cause chronic cough or chronic respiratory symptoms. Causes acute CAP.
Who should I test?
- Testing generally reserved for patients with severe CAP in hospital. Testing outside this should be discussed with the microbiologist.
- If there is suspicion of Legionella pneumonia in community patients, in most situations empiric treatment should be considered, rather than testing.
Test of choice:
Request Legionella PCR
PCR of sputum or other deep respiratory sample
- Excellent specificity – positive result confirms the diagnosis
- Good sensitivity – negative result (if good sample) makes diagnosis unlikely
Tests to avoid/specialist tests:
Urinary antigen – not recommended
- Poor sensitivity in the NZ context, as does not detect L.longbeachae, which is the commonest cause of Legionnaire’s disease in NZ.
Serology – not recommended
- Difficult to interpret, only used as part of a Public Health investigation.
- Requires acute and convalescent samples several weeks apart. Cannot confirm infection in a timeframe that is useful for informing treatment.
Other considerations:
Legionella pneumonia is a notifiable disease.