Rapid Urine Test Detects Legionella

Scientists at The Regional Laboratory of Public Health, (Haarlem, The Netherlands) evaluated an immunochromatographic urine antigen test (ICT) on 213 frozen urine samples that were unconcentrated from a sample collection of patients with and without LD that were collected between 2000 and 2011. They compared the results of the assay with another commercial test.

The test, called the TRU Legionella assay, has a conjugate tube containing a lyophilized bead of colloidal gold-linked polyclonal antibody to L. pneumophila serogroup 1 detector antibody. The test strip carries a nitrocellulose membrane with dried capture antibodies placed at a designated test line for Legionella. The test strip holder caps the conjugate tube during testing and subsequent disposal to reduce exposure to potential pathogens.

The sensitivity and specificity of the Meridian TRU Legionella assay (Meridian Bioscience; Cincinnati, OH, USA) were compared with the test results obtained by the widely used ICT assay, the Binax NOW urinary antigen test (Binax; Portland, ME, USA). Both antigen tests were performed simultaneously and the results were interpreted at 15 minutes for the Binax NOW test and at 20 minutes for Meridian TRU Legionella strip. To investigate if a prolonged incubation time would affect the sensitivity, the samples were also read at 30, 45, and 60 minutes of incubation.

The sensitivity was estimated as 73.3% for the Meridian TRU Legionella test and 76.3% for the Binax NOW urine antigen test. The specificity was 100% for both assays. There were five samples, which were positive in the Binax NOW and negative in the Meridian TRU Legionella test, and those five samples were all positive in an enzyme immunoassay-control test. After a prolonged incubation, the same five samples were also positive in the Meridian TRU Legionella test. When the tests were re-examined after 60 minutes of incubation the sensitivity of the Meridian TRU Legionella test increased to 80.6 % and to 81.3 % for the Binax NOW urine antigen test.

The authors concluded that both assays evaluated have similar performance characteristics and are suitable for the detection of L. pneumophila antigen in urine from patients suspected of having LD. As the prolongation of incubation does not affect the specificity, it is recommended that an incubation time longer than that recommended by the manufacturer be used routinely. The study was published in the March 2013 issue of the European Journal of Clinical Microbiology & Infectious Diseases.

Related Links:
Dutch Regional Laboratory of Public Health
Meridian Bioscience
Binax