(From the article by T. Shimada, Y. Noguchi, J.L. Jackson, J. Miyashita, Y. Hayashino, T. Kamiya, Sh. Yamazaki, T. Matsumura, S. Fukuhara in CHEST)
The Legionella urinary antigen test is the most frequently used method to diagnose Legionnaires’ disease because of its simplicity and rapidity of results. It also has very good specificity for Legionella pneumophila serogroup 1 (the most common bacteria type for Legionnaires’ disease), but low sensitivity.
A systematic review and meta-analysis of urinary antigen tests for Legionellosis was done by a group of researchers in Japan and the U.S. in order to “assess the test characteristics of Legionella urinary antigen. The 2008 study performed by these researchers found that there was a 26% false-negative rate when using the urinary antigen test for Legionella. This means that over a quarter of patients confirmed for Legionellosis also had a negative urinary antigen test result.
Because of this finding, it is recommended that if L. pneumophila is suspected to be the cause of illness, Legionella antibiotic treatment for patients should not cease even if a negative urine antigen test results.
Shimada, T.; Noguchi, Y.; Jackson, J.L.; Miyashita, J.; Hayashino, Y.; Kamiya, T.; Yamazaki, S.; Matsumura, T.; Fukuhara, S. (2009). Systematic Review and Metaanalysis – Urinary Antigen Tests for Legionellosis. CHEST 136:1576-1585.