Test performance study to evaluate diagnostic tests for the detection and identification of Xylophilus ampelinus in vine material spiked with cells from X. ampelinus cultures

Abstract

A test performance study (TPS) was conducted in 2020 to evaluate performance of serological and PCR-based tests for the detection of Xylophilus ampelinus in homogenised vine samples. In total, 11 labs participated, although there were fewer participants for the serological tests than the PCR-based tests. The panel of samples sent to participants included spiked samples containing 104–108 cfu per ml (serological tests) or 102–106 cfu per ml (PCR-based tests) as well as positive and negative controls. The five PCR-based tests were found to be fit for purpose, with similar performance across a range of metrics (analytical sensitivity, diagnostic sensitivity and specificity, and repeatability and reproducibility assessed in terms of accordance and concordance, respectively). Serological methods (two immunofluorescence tests and two ELISA tests) were found to be less sensitive with regard to both analytical and diagnostic sensitivity. Furthermore, the occurrence of false positives suggests that a positive IF result may not be conclusive when considered in isolation. One of the ELISA tests exhibited much lower analytical and diagnostic sensitivity than the other serological tests and would not be considered suitable for the purpose considered by this TPS.