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

Background: Diphtheria is a potentially fatal disease caused by toxigenic strains of Corynebacterium diphtheriae, C. ulcerans or C. 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 were C. diphtheriae (n = 18) and C. ulcerans (n = 15). Most C. diphtheriae cases were cutaneous (14/18) while more than half of C. ulcerans cases had respiratory presentations (8/15). Two thirds (23/33) 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 (441/507; 87%) submitted for toxigenicity testing were non-toxigenic, however, toxin positivity rates were higher (15/23) for C. ulcerans than C. diphtheriae (18/469). Ten non-toxigenic toxin gene-bearing (NTTB) C. diphtheriae were also detected. Conclusion: Diphtheria 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.