TOX and diphtheria: Despite reassurances that the vast majority of C. diphtheriae isolated from clinical samples in Ontario are nontoxigenic, several factors advise appropriate vigilance regarding C. diphtheriae infections, including multiple recent diphtheria outbreaks reported globally, human travel-related transmission potentially facilitated by asymptomatic carriage, potential for decreased vaccine efficacy due to tox gene evolution, vaccine hesitancy, and the potential for nontoxigenic C. diphtheriae to cause serious invasive disease.