the changing epidemiology of diphtheria in the united kingdom 2009 to 2017 backgrounddiphtheria is a potentially fatal disease caused by toxigenic strains of corynebacterium diphtheriae c ulcerans or c pseudotuberculosisaimour objective was to review the epidemiology of diphtheria in the united kingdom uk and the impact of recent changes in public health management and surveillancemethodsputative human toxigenic diphtheria isolates in the uk are sent for species confirmation and toxigenicity testing to the national reference laboratory clinical epidemiological and microbiological information for toxigenic cases between 2009 and 2017 are described in this populationbased prospective surveillance studyresultsthere were 33 toxigenic cases of diphtheria aged 4 to 82 years causative species were c diphtheriae n18 and c ulcerans n15 most c diphtheriae cases were cutaneous 1418 while more than half of c ulcerans cases had respiratory presentations 815 two thirds 2333 of cases were inadequately immunised two cases with c ulcerans infections died both inadequately immunised the major risk factor for c diphtheriae aquisition was travel to an endemic area and for c ulcerans contact with a companion animal most confirmed c diphtheriae or c ulcerans isolates 441507 87 submitted for toxigenicity testing were nontoxigenic however toxin positivity rates were higher 1523 for c ulcerans than c diphtheriae 18469 ten nontoxigenic toxin genebearing nttb c diphtheriae were also detectedconclusiondiphtheria is a rare disease in the uk in the last decade milder cutaneous c diphtheriae cases have become more frequent incomplete vaccination status was strongly associated with the risk of hospitalisation and death