Diagnostic Use
Legionella is an uncommon cause of community-acquired pneumonia in New Zealand.
The rate is < 10/100,000 population. About two-thirds of all cases are caused by Legionella longbeachae.
The preferred diagnostic test is PCR performed on lower respiratory tract specimens.
The Legionella urinary antigen test is quick but it only detects infection with the L.pneumophila serogroup 1. This serogroup is an uncommon cause of infection in New Zealand compared to other countries. The overall sensitivity of the test on concentrated urine is about 75 – 80% (may sometimes be lower or higher with mild or severe disease respectively). The specificity is high. Note that a negative test does not rule out other Legionella sp. as the cause of infection.
This test should not be done routinely on patients presenting with uncomplicated community-acquired pneumonia, especially children and young adults (< 50 years of age).