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Comparative Study
. 2017 Dec 26;56(1):e01440-17.
doi: 10.1128/JCM.01440-17. Print 2018 Jan.

Evaluation of In-House and Commercial Serological Tests for Diagnosis of Human Tularemia

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Free PMC article
Comparative Study

Evaluation of In-House and Commercial Serological Tests for Diagnosis of Human Tularemia

Hadjila Yanes et al. J Clin Microbiol. .
Free PMC article

Abstract

Tularemia is a zoonosis caused by the bacterium Francisella tularensis Its specific diagnosis remains based on serological methods, while F. tularensis is rarely detected in clinical samples by culture or PCR. The aim of the present study was to evaluate the performance of the Serion enzyme-linked immunosorbent assay (ELISA) classic Francisella tularensis IgG and IgM tests (Virion/Serion GmbH Institute, Würzburg, Germany) and the VIRapid tularemia immunochromatographic test (ICT) (Vircell, Granada, Spain) compared to that of the in-house microagglutination test (MAT) and indirect immunofluorescence assay (IFA) currently used at the French National Reference Center for Francisella We evaluated 256 consecutive sera from 208 patients, including 51 confirmed and 23 probable tularemia cases, and 134 control patients not infected with F. tularensis The IFA tests displayed 72.5% sensitivity for IgM (cutoff titer ≥80) and 74.5% for IgG (cutoff titer ≥160), and 99.3% specificity for both IgM and IgG. Using cutoffs advocated by the manufacturer, the Serion ELISAs displayed 88.2% sensitivity for IgM and 86.3% for IgG antibodies; specificity was 94.8% for IgM and 95.5% for IgG. Compared to MAT and IFA tests, the Serion ELISAs allowed earlier detection of specific antibodies (1 to 2 weeks versus 2 to 3 weeks after the onset of symptoms). The ICT sensitivity and specificity were 90% and 83.6%, respectively, when considering the cutoff advocated by the manufacturer. In conclusion, the Serion ELISAs are useful as screening tests for tularemia diagnosis, but additional confirmatory tests (such as MAT and IFA) are needed, especially in areas of low endemicity.

Keywords: ELISA; Francisella tularensis; immunochromatography; immunofluorescence assay; serology; tularemia; zoonosis.

Figures

FIG 1
FIG 1
ROC curves for detection of IgM or IgG anti-F. tularensis antibodies using immunofluorescence assays (IFAs) or ELISAs. AUC, area under the curve.
FIG 2
FIG 2
Negative predictive values (NPVs) and positive predictive values (PPVs) according to tularemia prevalence of ELISA-IgM (top)and ELISA-IgG (bottom) tests, using either the lower cutoff titers recommended by the manufacturer (dashed line) or the higher cutoff titers of 0.9 for IgM and 1.4 for IgG (solid line) defined herein to increase specificity.

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