Legionella

• 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.

Does not cause chronic cough or chronic respiratory symptoms. Causes acute CAP.

• 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.

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

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.

Legionella pneumonia is a notifiable disease