Evaluation of Two New Immunochromatographic Assays (Rapid U Legionella Antigen Test and SD Bioline Legionella Antigen Test) for Detection of Legionella pneumophila Serogroup 1 Antigen in Urine

Abstract

We evaluated two new immunochromatographic assays for their abilities to detect Legionella pneumophila serogroup 1 antigen in urine. The results were compared with those obtained by the Binax NOW urinary antigen test. The sensitivities and specificities were estimated to be 71.2% and 96.6%, respectively, for the Rapid U test; 31.5% and 98.9%, respectively, for the SD Bioline test; and 91.8% and 100%, respectively, for the Binax NOW test.Legionnaires' disease (LD) is a pneumonia responsible for 1 to 5% of cases of community-acquired pneumonia (CAP) requiring hospital admission (3,15). Legionella pneumophila causes 91% of all reported cases of LD, with serogroup 1 being the most predominant serogroup, causing approximately 80% of all culture-confirmed cases (12). However, this percentage is found to be lower in some European countries (10). Since antigen detection in urine has proved to be a sensitive and rapid method for the detection of L. pneumophila serogroup 1, this technique has become one of the most-used tools for the diagnosis of LD (10). An immunochromatographic (ICT) assay (the Binax NOW legionella urinary antigen test) that has a sensitivity and a specificity similar to those of enzyme immunoassays (EIAs) has been developed (4). ICT assays have important advantages over conventional EIAs: the tests are simple to perform, they do not require special laboratory equipment, and results can be obtained within 15 min.The aim of our study was to evaluate two newly developed ICT urine antigen tests, the Rapid U Legionella antigen test (Rapid U test; Diamondial, Sees, France) and the SD Bioline Legionella urinary antigen test (SD Bioline test; Standard Diagnostics, Inc., Kyonggi-do, Korea), for the detection of L. pneumophila serogroup 1 in urine. Neither test is yet commercially available.We evaluated the abilities of the new antigen tests to diagnose LD in a well-described sample of patients with and without LD using frozen urine samples. Urine samples were collected between 1997 and 2005 and were stored at Ϫ70°C until processing was performed. We included 73 urine samples from 73 patients with LD (cases). A case of LD was defined as a patient with pneumonia who had radiological signs of infiltration and who showed laboratory evidence of infection with L. pneumophila. One or more of the following criteria constituted laboratory evidence of infection with L. pneumophila: isolation of L. pneumophila from a lower respiratory tract (LRT) sample, a positive PCR result with an LRT sample by a 16S rRNAbased assay (16), or seroconversion to positivity for immunoglobulin M (IgM) and/or IgG antibodies to L. pneumophila in paired acute-phase and convalescent-phase sera by a commercial enzyme-linked immunosorbent assay

Legionella spp. and Legionnaires' disease

“…71,72 The Binax NOW urinary antigen test, in concordance with the findings of previous studies, has excellent sensitivity and specificity. The performance of some new tests are below the acceptable level for diagnostic assays.…”

“…The performance of some new tests are below the acceptable level for diagnostic assays. 71 Detection of Legionella nucleic acid…”

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…These complications were confirmed in several research studies, where presumably low antigen excretion presented "delayed positive" ICT results (using the BinaxNOW Legionella ICT) observed at later time points (e.g., after 1 to 4 h of incubation) for samples initially giving borderline EIA absorbance measurements (267,268,276,308). However, with some commercial products, this procedure may occasionally yield false-positive results, and manufacturers typically do not endorse this method of use (with some exceptions, e.g., Oxoid Xpect); in any case, results should be interpreted with caution if this method is performed (278,309). In general, if initial UAT results are negative but the index of suspicion for LD remains high, clinicians are encouraged to perform testing multiple times over a longer period and/or to employ alternative testing modalities, such as PCR (283,305), and additionally, concentrating urine can increase sensitivity without decreasing specificity (266,279,283,306); however, boiling to reduce nonspecific interactions may be advised.…”

“…To date, one company has applied research toward a potential pan-Legionella rapid ICT (SD Bioline Legionella) using this antigen. Despite an initial negative review, this ICT was compared favorably to the Alere BinaxNOW Legionella UAT for Lp1 diagnosis; however, further evaluation is needed to assess its potential for non-sg1 disease diagnosis (309,585).…”

Evaluation of the Oxoid Xpect Legionella Test Kit for Detection of Legionella pneumophila Serogroup 1 Antigen in Urine

“…We studied a panel of frozen nonconcentrated urine samples collected between 1995 and 2005 from 86 patients with pneumonia caused by L. pneumophila (cases) (3). LD patients were admitted with pneumonia, had radiological signs of infiltration, and showed laboratory evidence of infection with L. pneumophila.…”