Legionella pneumonia is increasingly diagnosed only with urinary antigen rather than cultures, which are often no longer obtained in most hospitals. If UA is positive, how does one then link to enviroinmental samples?
As you know, the urinary antigen detects only L. pneumophila, serogroup 1.
If the Legionella in the environmental water sample is also L. pneumophila, serogroup 1, it is weak circumstantial evidence that the water may be the source. In essence, a positive match might be less useful than a negative match; a negative match might rule out the water as the source. This assumes that the water sample is performed as rigorously as our Special Pathogens Lab which uses multiple selective media and heat/acid treament to exclude contaminating flora.