title: Detection of Echinococcus multilocularis by MC-PCR: evaluation of diagnostic sensitivity and specificity without gold standard.
abstract: BACKGROUND
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  The sensitivity of the MC-PCR (0.88) was comparable to the sensitivity of SCT (0.83).
authors.affiliation: Department of Disease Control and Epidemiology, National Veterinary Institute, Uppsala, Sweden; Helene.wahlstrom@sva.se.
authors.forename: Helene
authors.initials: H
authors.lastname: Wahlström
authors.affiliation: Department of Disease Control and Epidemiology, National Veterinary Institute, Uppsala, Sweden.
authors.forename: Arianna
authors.initials: A
authors.lastname: Comin
authors.affiliation: Department of Microbiology, National Veterinary Institute, Uppsala, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Isaksson
authors.affiliation: Institute of Parasitology, Vetsuisse and Medical Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Deplazes
keywords: Echinococcus multilocularis; PCR; SCT; latent class analysis; sensitivity; specificity