Ya en su dictamen científico de enero de 2015, la EFSA concluía que los olivos sintomáticos estaban, en general, afectados por un complejo de plagas y patógenos, incluidos Xylella fastidiosa, varios hongos y el insecto Zeuzera pyrina.Sin embargo, aunque aún no se conoce plenamente el papel específico de Xylella fastidiosa en el síndrome de decaimiento rápido del olivo, se ha comprobado la presencia de dicha bacteria en plantas jóvenes con signos de este síndrome, sin que se encontraran otros patógenos.
Already in the Scientific Opinion of January 2015, EFSA concluded that olive trees showing symptoms of the bacterium, were generally affected by a multitude of pests and pathogens including Xylella fastidiosa¸ several fungi and Zeuzera pyrina (commonly known as the 'leopard moth'). However, although the specific role of Xylella fastidiosa in the quick "decline syndrome of olive" remains to be fully understood, Xylella fastidiosa has been found in young plants showing signs of the declining syndrome, where no other pathogens where found.