Incidence of Legionella Pneumonia as Diagnosed by Urinary Legionella Antigen Testing: A Retrospective Analysis

Abstract

PURPOSE: To evaluate the incidence of Legionella pneumonia, as diagnosed by the urinary Legionella antigen in a cohort of hospitalized patients, and to determine the usefulness of testing for infection in patients with upper respiratory illness and severe pneumonia. METHODS: Data was collected retrospectively on hospitalized patients from February 1, 2000 to April 7, 2010, who had been tested for Legionella pneumonia via the urinary antigen. The Binax Now Legionella urinary antigen (Binax, Inc., Scarborough, Maine) was used for testing purposes. RESULTS: Five thousand five hundred and forty-three inpatient tests were conducted. Eleven (0.19%) had a positive antigen test. All patients with a positive antigen were treated appropriately on admission with either a respiratory fluoroquinolone or a macrolide. Since the year 2000, there was an exponential increase in the number of patients who were tested for infection, without a corresponding rise in positive results. CONCLUSION: The incidence of Legionella is extremely low (0.19%) in our cohort of hospitalized patients. The current international guidelines from the American Thoracic Society and the British Thoracic Society recommend testing of all patients with severe community acquired pneumonia for Legionella. All patients with positive results were treated empirically with appropriate antibiotics. Based on the aforementioned guideline recommendations, there has been a dramatic increase in the number of tests ordered. CLINICAL IMPLICATIONS: In our cohort of patients, the overwhelming number of tests ordered without significant benefit suggests that routine testing for legionella is not warranted.