Clinical utility of a Legionella pneumophila urinary antigen test in a large university teaching hospital.

OBJECTIVE

To determine the clinical utility of diagnosing Legionella pneumonia by urinary antigen testing (LPUAT) in a low prevalence centre.

DESIGN

The results of LPUATs were abstracted and analyzed from the authors' laboratory information system. Medical records were reviewed in detail for all positive tests and a random sample of 50 negative tests.

SETTING

The Queen Elizabeth II Health Sciences Centre, a large university hospital complex.

POPULATION STUDIED

Patients who were admitted from the emergency room with pneumonia or who had developed pneumonia in hospital and who had a LPUAT performed between April 1998 and October 2000.

MAIN RESULTS

One thousand one hundred fifty-four tests were performed on 1007 patients. Seven patients had nine positive LPUATs. Three of these patients had confirmed Legionella pneumophila pneumonia. Three others had probable or possible L pneumophila pneumonia. There was one probable false positive. Six of the seven patients were already on empirical anti-L pneumophila therapy. Of the 50 negative tests reviewed in detail, 31 patients were on one of the antibiotics of choice for L pneumophila at the time the test was ordered; in 21 (68%) of these patients the negative result did not lead to a change in therapy.

CONCLUSIONS

The cost to diagnose each case of Legionella pneumonia by LPUAT was approximately $5,770 and most patients were already on appropriate antibiotics. In patients with negative tests, antibiotics were often not changed in response to the test result. Rigorous screening of patients is required to increase pretest probability for LPUAT to be justified.