The changing epidemiology of diphtheria in the United Kingdom, 2009 to 2017

Background Diphtheria is a potentially fatal disease caused by toxigenic strains ofCorynebacterium diphtheriae, C. ulceransorC. pseudotuberculosis. Aim Our objective was to review the epidemiology of diphtheria in the United Kingdom (UK) and the impact of recent changes in public health management and surveillance. Methods Putative 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 population-based prospective surveillance study. Results There were 33 toxigenic cases of diphtheria aged 4 to 82 years. Causative species wereC. diphtheriae(n = 18) andC. ulcerans(n = 15). MostC. diphtheriaecases were cutaneous (14/18) while more than half ofC. ulceranscases had respiratory presentations (8/15). Two thirds (23/33) of cases were inadequately immunised. Two cases withC. ulceransinfections died, both inadequately immunised. The major risk factor forC. diphtheriaeaquisition was travel to an endemic area and forC. ulcerans,contact with a companion animal. Most confirmedC. diphtheriaeorC. ulceransisolates (441/507; 87%) submitted for toxigenicity testing were non-toxigenic,however, toxin positivity rates were higher (15/23) forC. ulceransthanC. diphtheriae(18/469). Ten non-toxigenic toxin gene-bearing (NTTB)C. diphtheriaewere also detected. Conclusion Diphtheria is a rare disease in the UK. In the last decade, milder cutaneousC. diphtheriaecases have become more frequent. Incomplete vaccination status was strongly associated with the risk of hospitalisation and death.