Evaluation of Rapid U Legionella Plus Test, a new immunochromatographic assay for detection of Legionella pneumophila serogroup 1 antigen in urine

Abstract

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 frequently used tools for diagnosing Legionnaires’ disease (LD) [1]. Currently, there are several commercially available tests for detecting L. pneumophila antigen in urine [2, 3]. Commercial kits that use enzyme immunoassay (EIA) methodologies have been available for several years and perform similarly. One immunochromatographic (ICT) assay (Binax NOW Legionella Urinary Antigen Test; Binax, Portland, Maine, USA) has similar sensitivity and specificity to EIA [2]. 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 the study presented here was to evaluate a newly developed ICT urine antigen test (the Rapid U Legionella Plus Test; Diamondial, Sees, France), for its ability to detect L. pneumophila serogroup 1 in urine. We evaluated the ability of the new antigen test to detect LD in a well-described sample of patients with and without LD using frozen urine samples. The samples had been collected between 1997 and 2005 and stored at −70°C until processing. We included 71 urine samples obtained from 71 patients with LD (cases). A case of LD was defined as a patient with pneumonia who had radiological signs of infiltration and laboratory evidence of infection with L. pneumophila. Laboratory evidence included one or more of the following criteria: isolation of L. pneumophila from a lower respiratory tract (LRT) sample; a positive PCR result on a LRT sample using a 16S rRNA-based assay [4]; seroconversion to positive IgM and/or IgG antibodies against L. pneumophila in paired acute-phase and convalescentphase sera using a commercial ELISA (Serion ELISA; Institut Virion\Serion, Wurzburg, Germany). All LD-positive samples tested negative for pneumococcal antigen in urine (PAG; Binax NOW, Portland, Maine, USA). Urine samples of 91 patients with respiratory tract infections caused by pathogens other than Legionella were tested in a similar manner to test specificity. All patients were tested for LD using an immunochromatographic assay (Binax NOW); all samples tested negative. The laboratory results for these patients tested with blood cultures (blood), PAG detection in urine (PAG) and sputum culture (sputum) were as follows: Streptococcus pneumoniae (n=52 patients: detected in sputum in 8 patients, in blood and PAG in 23, and in blood alone in 21), Haemophilus influenzae (n=10: blood, 3; sputum, 7), Moraxella catarralis (n=3: all in sputum), Staphylococcus aureus (n=4: blood and sputum, 2; sputum, 2), Escherichia coli (n=2: blood and sputum, 1; sputum alone, 1), Acinetobacter baumannii (n=1: blood and sputum), Streptococcus pyogenes (n=2: both blood and sputum), Klebsiella pneumoniae (n=1: sputum), Mycobacterium tuberculosis (n=3: all sputum), Pneumocystis jirovecii (n=1: Giemsa and silver-stain positive). Twelve patients with a fourfold or greater rise in (complement-fixating) antibodies against influenza A virus (n=3), adenovirus (n=1), Chlamydia psittaci (n=3), Mycoplasma pneumoniae (n=4) and parainfluenza virus (n=1) were included. The presence of L. pneumophila antigen in urine samples was investigated using Rapid U Legionella Plus Test, a qualitative ICT assay. We compared the sensitivity and specificity of this test with that of a widely used ICT assay, the Binax Now urinary antigen test (Binax NOW). Eur J Clin Microbiol Infect Dis (2006) 25:733–735 DOI 10.1007/s10096-006-0213-0