Legionnaire’s disease can be diagnosed by testing for
antigen in the urine of infected patients and most cases are diagnosed using this method. However, urine antigen testing only identifies
serogroup 1. All
species and serogroups can be identified by culture of sputum or bronchoalveolar lavage specimens, but culture is less sensitive in patients who have already begun antibiotic therapy.
Testing for legionellosis should be considered particularly in patients who have failed outpatient antibiotic therapy for community-acquired pneumonia and patients with severe pneumonia, such as those requiring intensive care.