After seeing Seina's condition firsthand and discovering its source, Izroth was indeed confident in curing her. However, there was one glaring issue at hand.
'Assuming that those great masters who paid a visit are not all working together to deceive the Holy Maiden, whatever unspecified substance was used to poison her is capable of evading their eyes. This type of poison should be scarce and not easy to come by. This means that as long as I can uncover the identity of the substance that was used, I should be able to pinpoint its origins.'
Since the Holy Maiden was a high-ranking Apothecary, even if she were in a weakened state, she should have discovered the presence of an unknown substance on the tea leaves. This is why Izroth leaned away from the fact that those healing experts were working together with someone to deceive her. But, this also revealed the vicious nature behind the poison.