Comparison of Diagnostic Sensitivities of Three Assays (Bartels Enzyme Immunoassay [EIA], Biotest EIA, and Binax NOW Immunochromatographic Test) for Detection of Legionella pneumophila Serogroup 1 Antigen in Urine

Abstract

The Bartels enzyme immunoassay (EIA), Biotest EIA, and Binax NOW immunochromatographic test (ICT) urinary antigen kits for the detection of Legionella pneumophila serogroup 1 were compared using 178 frozen urine samples. When nonconcentrated urine samples were used, the sensitivity levels of both enzyme EIAs were significantly higher than the sensitivity level of the ICT (Bartels EIA, 71.3%; Biotest EIA, 65.1%; Binax NOW ICT, 37% [P < 0.001]). After concentration of the urine samples, no significant differences in sensitivity were found among the three tests.Laboratory diagnosis of Legionella pneumophila infection is performed on the basis of the results of culture growth, direct immunofluorescence, serologic testing, and antigen detection in urine. Since antigen detection in urine has proved to be a sensitive and rapid method for detecting L. pneumophila serogroup 1, this technique has become one of the most used tools for the diagnosis of Legionnaires' disease. The urinary antigen test permits early diagnosis and initiation of appropriate antibiotic therapy (9), and it leads to the recognition of outbreaks of Legionnaires' disease, allowing a rapid epidemiological investigation (10, 11, 13). Currently, there are several commercially available tests (the Binax Legionella urinary antigen enzyme immunoassay [EIA], the Biotest Legionella urine antigen EIA, and the Binax NOW Legionella urinary antigen immunochromatographic test [ICT]) for the detection of L. pneumophila antigen in urine. All of these tests have been previously evaluated, confirming their utility for the diagnosis of Legionnaires' disease (6,12). A wider range of sensitivity has been reported, however, although no research has demonstrated significant differences in sensitivity between these tests. Recently a new EIA (Bartels Legionella Urinary Antigen) for the detection of L. pneumophila serogroup 1 antigen in urine has been developed. We evaluated this new test by comparing its sensitivity to that of two widely used tests: the Biotest EIA and the Binax NOW ICT.A total of 178 urine specimens (obtained from patients with Legionnaires' disease during an outbreak which occurred in Murcia, Spain, in July 2001) were included in the study. The samples were from patients who fulfilled the epidemiological criteria, suffered from symptoms compatible with pneumonia, and showed radiological signs of infiltration and for whom Legionnaires' disease was confirmed either by culture (defined as isolation of L. pneumophila serogroup 1 from respiratory specimens) or serology (defined as a fourfold increase in L. pneumophila serogroup 1 antibody titer in paired sera or, in patients with clinically compatible illness, a high [Ն 256] stationary titer value).During the outbreak, nonconcentrated urine samples were tested within a few hours after receipt by using Biotest EIA (182 were positive and 47 were negative); the samples were then frozen at Ϫ80°C. Samples were retested simultaneously using the Biotest Legionella urine antigen EIA (Biotest AG, Dreieich, Germany), Bi...

Value of Serological Testing for Diagnosis of Legionellosis in Outbreak Patients

“…In the present study, antigen detection was by far the most sensitive technique for detecting legionellosis in first samples drawn at patient admission; its sensitivity was slightly over 50%, thus broadly agreeing with recent surveys reporting a sensitivity of 60 to 70% (16,22,26). In a previous study of samples from different patients belonging to the same outbreak, a sensitivity of 69.6% was recorded for the Binax NOW antigenuria test performed on concentrated samples (9). This higher sensitivity value is probably attributable to the inclusion only of samples from patients with positive diagnoses of legionellosis by serology and/or culturing; a positive correlation between test sensitivity and clinical severity has been documented (26).…”

Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations

“…However, sensitivities among commercially available tests for non-Lp1 LD are highly variable and generally much lower than those for Lp1-associated disease when assayed with urine from patients with confirmed LD (267,(270)(271)(272)(273)(274)(275). Importantly, the sensitivities of most similar-format UATs are generally equivalent, regardless of the manufacturer (267)(268)(269)(276)(277)(278)(279), and they all allow for rapid assessment and patient treatment (280)(281)(282), unlike culture or serology, which may take days to weeks (139). Overall, the card-based ICT is a rapid, simple, qualitative assay for basic laboratory or POC use, while the EIA format is quantitative, may offer comparatively higher sensitivity and specificity, and is more suited for larger clinical, reference, or research laboratories (283).…”

“…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. These additional steps would likely abrogate the time advantages of the rapid ICT.…”

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

“…Based on prospective and retrospective studies with data from solitary cases, moderate to high urinary antigen test sensitivities have been described, ranging from 56 to 99% (2,5,6,8,13). This may be explained by differences in test and patient characteristics, the serogroup with which the patient is infected, the timing of specimen collection in the course of the illness, and whether the urine is concentrated before it is tested.…”