Laboratory diagnosis of legionnaires’ disease due to Legionella pneumophila serogroup 1: comparison of phenotypic and genotypic methods

Abstract

Laboratory results of 67 cases of legionnaires' disease caused by Legionella pneumophila serogroup (Sg) 1 spanning a 6-year period were analysed by both phenotypic and genotypic methods. The methods compared were urinary antigen enzyme immunoassay (EIA), an immunofluorescent antibody (IFA) test, direct fluorescent antibody (DFA), culture and a 5S rRNA PCR with Southern blotting confirmation. Urine was available in 53 cases, of which 35 (66 %) were positive, with an antigen peak observed at 5-10 days after onset of disease symptoms. The IFA test was positive in 62 (92 . 5 %) cases, with 56 (90 . 3 %) cases producing a greater than fourfold rise in titre and 6 (9 . 7 %) giving presumptive high titres of >1 : 128. There were two antibody peaks, one at 10-15 days and another at .25 days after onset. In 23 cases where samples were available, DFA and culture were respectively positive in 5 (22 %) and 10 (48 %) cases. There was a peak in culturepositives 5-10 days after onset of disease. A Legionella-specific 5S rRNA PCR on patient serum was positive in 54 (80 . 5 %) cases, with a peak in PCR positivity at 6-10 days after disease onset. In 22 of the 67 cases, the full panel of diagnostic methods was available for comparison. The relative sensitivity and specificity of the urinary antigen EIA and the serum PCR was 100 %. The IFA gave relative sensitivity and specificity values of 93 . 8 and 95 %. DFA and culture, although 100 % specific, produced only low sensitivities, of 19 and 42 . 8 %, respectively. This study has shown that urinary antigen and serum PCR are valuable tests in the acute phase of disease, with excellent sensitivity and specificity values. At present, the Legionella species causing infection requires to be verified by IFA serology and/or culture, but this could become unnecessary as new antigen and L. pneumophila Sg 1-specific PCR tests become available.

Value of Serological Testing for Diagnosis of Legionellosis in Outbreak Patients

“…Although antigen detection remains the best method for the early diagnosis of legionellosis, the results obtained here support the suggestion made by other authors (12,16) that other laboratory methods, including those aimed at detecting antibodies, may provide a valuable complement. Of these, IgM detection by ELISA proved here to be the best alternative.…”

“…This method has been reported to show very good sensitivity values (10,13,17). 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).…”

“…In a recent study, sensitivities of 66% and 92.5% were reported for antigen detection and IFA, respectively (16). Taking into account the large number of patients not evaluable in some IFAs due to the lack of second suitable samples, ELISA for IgM proved to be the best of the serological tests, showing a high statistical significance (P Ͻ 0.01) when compared with antigenuria detection.…”

Limited Applicability of Direct Fluorescent-Antibody Testing for Bordetella sp. and Legionella sp. Specimens for the Clinical Microbiology Laboratory

“…In this study, less than 0.5% of more than 12,000 specimens tested positive by the DFA method, and DFA testing detected only 2 of the 19 specimens found to be culture positive for L. pneumophila. Previous studies corroborate our finding of a low sensitivity of DFA testing versus culture (8,9). Our numbers were too small to adequately assess the DFA method compared to PCR, precluding statistically significant conclusions in this case.…”

The role of atypical respiratory pathogens in exacerbations of chronic obstructive pulmonary disease

“…The primers of the first Legionella spp. PCR-probe assay are based on the primers described by LINDSAY et al [22], and detected in real time using a TaqMan probe Leg5S (Applied Biosystems, Nieuwerkerk a/d Ijssel, the Netherlands) [23]. The second PCR was a L. pneumophila-specific PCR based on the sequences of the mip gene [23].…”