A proficiency test (PT) to evaluate the performance of laboratories involved in molecular
and serological detection of X. fastidiosa was carried out in early 2017; 35 laboratories from EU/non-
EU Countries tested 4 different methods to purify DNA, conventional and qPCR assays, and 2 ELISA
tests. The number of resultant positive agreement/negative agreement/positive deviation/negative
deviation was used to determine the laboratory performance (i.e. accuracy 100%). The overall results
showed that all laboratories were able to correctly diagnose X. fastidiosa in the blind samples containing the highest X. fastidiosa concentrations, whereas the performance of several laboratories
was negatively affected by the lack of detection in the samples with the lowest concentrations, both
through molecular and serological tests. Accuracy level of 100% (laboratory conformed to the PT) was
successfully recovered in the majority of the laboratories performing qPCR and PCR assays on DNA
purified using at least 2 of the 4 tested protocols. The use of automated platform ensured higher
laboratory performance. As expected, results of the ELISA tests generated lower performance values
in the majority of the laboratories, due to the lack of detection of positive samples containing the
lowest the bacterial concentration. This study provides a good overview on the laboratory
performance for the diagnostics currently used in the EPPO countries and indicate useful
improvements that laboratories can adopt to achieve a better performance