Urinary Antigen Assay Detects Legionella

Laboratory diagnosis of Legionella pneumophila infections in patients with pneumonia is based on culture, serological testing, molecular testing, and detection of soluble L. pneumophila antigen in urine.

Scientists at the Regional Laboratory of Public Health (Haarlem, The Netherlands) tested frozen urine samples from a well-described sample of patients with and without LD. Urine samples were collected between 1997 and 2010 and were stored at -70 °C until processing was performed. These included 58 urine samples from 58 patients with LD. The specificity of the test was determined by using urine samples collected from 38 patients with respiratory tract infections other than Legionella infections.

The SD Bioline Legionella Urinary Antigen test (Standard Diagnostics Inc., Kyonggi-do, Korea) was compared with those obtained by the BinaxNOW Legionella Urinary Antigen enzyme immunoassay (EIA) (Galway, Ireland). A total of 96 samples were tested with the SD Bioline and BinaxNOW test. SD Bioline test was positive for 46/58 samples with sensitivity of the assay estimated as 79%. The BinaxNOW urinary antigen test was positive 47/58, with a sensitivity of 81%. These results were obtained after 15 minutes of incubation. The difference in sensitivity between SD Bioline test and BinaxNOW is comparable. Both tests were negative in the 38 samples from the non-Legionella patients giving a specificity of 100% for both assays.

LD is an acute pneumonia caused by Legionella species, which are non-spore-forming Gram-negative rods. L. pneumophila serogroup 1 accounts for more than 90% of human infections and is the most important etiological agent of LD. It is estimated that 8,000-18,000 cases of Legionnaires' disease occur in the USA each year. The authors concluded that the findings of the evaluation indicate that the SD Bioline test is both sensitive and specific and could be a good alternative for the detection of L. pneumophila serogroup 1 antigen in urine from patients suspected of having LD. The study was published in the January 2012 edition of the Journal of Infection.

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Regional Laboratory of Public Health
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