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. 2016 Mar 9:6:30173.
doi: 10.3402/iee.v6.30173. eCollection 2016.

Detection of Echinococcus multilocularis by MC-PCR: evaluation of diagnostic sensitivity and specificity without gold standard

Helene Wahlström  1 , Arianna Comin  2 , Mats Isaksson  3 , Peter Deplazes  4
Affiliations

Detection of Echinococcus multilocularis by MC-PCR: evaluation of diagnostic sensitivity and specificity without gold standard

Helene Wahlström et al. Infect Ecol Epidemiol. .

Abstract

Introduction: A semi-automated magnetic capture probe-based DNA extraction and real-time PCR method (MC-PCR), allowing for a more efficient large-scale surveillance of Echinococcus multilocularis occurrence, has been developed. The test sensitivity has previously been evaluated using the sedimentation and counting technique (SCT) as a gold standard. However, as the sensitivity of the SCT is not 1, test characteristics of the MC-PCR was also evaluated using latent class analysis, a methodology not requiring a gold standard.

Materials and methods: Test results, MC-PCR and SCT, from a previous evaluation of the MC-PCR using 177 foxes shot in the spring (n=108) and autumn 2012 (n=69) in high prevalence areas in Switzerland were used. Latent class analysis was used to estimate the test characteristics of the MC-PCR. Although it is not the primary aim of this study, estimates of the test characteristics of the SCT were also obtained.

Results and discussion: This study showed that the sensitivity of the MC-PCR was 0.88 [95% posterior credible interval (PCI) 0.80-0.93], which was not significantly different than the SCT, 0.83 (95% PCI 0.76-0.88), which is currently considered as the gold standard. The specificity of both tests was high, 0.98 (95% PCI 0.94-0.99) for the MC-PCR and 0.99 (95% PCI 0.99-1) for the SCT. In a previous study, using fox scats from a low prevalence area, the specificity of the MC-PCR was higher, 0.999% (95% PCI 0.997-1). One reason for the lower estimate of the specificity in this study could be that the MC-PCR detects DNA from infected but non-infectious rodents eaten by foxes. When using MC-PCR in low prevalence areas or areas free from the parasite, a positive result in the MC-PCR should be regarded as a true positive.

Conclusion: The sensitivity of the MC-PCR (0.88) was comparable to the sensitivity of SCT (0.83).

Keywords: Echinococcus multilocularis; PCR; SCT; latent class analysis; sensitivity; specificity.

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