EFSA pest survey card on Xylella fastidiosa: how to define the detection method?

EFSA developed the “Pest survey card on Xylella fastidiosa” for the preparation of surveys, with the aim of guiding the Member States in gathering information needed for designing statistically sound and risk-based surveys for the pathogen. In particular, it addresses the key question on how to detect the organism. The method of detection needs to be defined and consists of a sequence of operations starting from the selection of the units to inspect, the inspection itself, the sampling of plant material and finally the diagnostic and testing in the laboratory using available protocols. The inspection unit is the elementary subdivision of the host plant population targeted by the survey and to which the detection method is applied. For X. fastidiosa, the inspection units are the individual host plants. A major challenge for the detection of the bacterium is that both symptomatic and asymptomatic plant material should be scrutinised and systematically sampled. This is because infected plants can be asymptomatic for a long and variable period, and symptoms can be confused with drought-induced stress and other biotic or abiotic stresses. Nonetheless, an accurate visual examination to detect Xylella-like symptoms plays a major role during the collection of samples. The performance of the detection method, defined as the overall method sensitivity, should be estimated based on the available information. It is suggested to combine the sampling effectiveness, related to the sampling procedures, and the diagnostic sensitivity, defined by the laboratory tests. Characterising the detection method and its overall sensitivity is necessary for designing a robust survey, and to calculate the survey effort required to detect the pest in terms of number of inspections, samples, and laboratory tests.