Since the presence of the tox gene does not necessarily determine the production of DT—as non-toxigenic strains bearing the tox gene (NTTB) of C. diphtheriae, C. ulcerans, and C. pseudotuberculosis have been reported [19,57,58,59,60,61]—all positive NAATs results in patients suspected of diphtheria must be phenotypically confirmed, for example, by the Elek test [22]. This evidence concerns the gene TOX and diphtheria.