Etymology
Borrowed from Italian inficiare + English -ate (suffix forming verbs), from Medieval Latin īnficior, alteration of Classical Latin īnfitior (“to deny, contradict”), from *īnfitiae (“denial”) (see īnfitiās eō), from fateor (“to admit, acknowledge”).
Presumably originally a mistranslation by Italian speakers; compare aprimorate (“to elevate, improve”), taken from Portuguese in a similar manner.
Earlier mentions of the word in Randle Cotgrave and Henry Cockeram's Early Modern English dictionaries are likely unconnected to the modern borrowing from Italian.