UK NTTB study
The combination of PCR and the Elek test to identify toxigenic corynebacteria by the presence of both the diphtheria toxin gene (tox) and diphtheria toxin expression, has revealed organisms described as non-toxigenic toxin-gene bearing (NTTB) Corynebacterium diphtheriae or C. ulcerans (i.e., PCR tox positive; Elek negative). These organisms carry part or all of the diphtheria toxin gene but are unable to express functional toxin and present a challenge to their clinical and public health management.    There is little data on the theoretical risk of NTTB reverting to becoming fully toxigenic. This unique cluster and subsequent epidemiologically linked isolates recovered over a 7-year period allowed the opportunity to determine if there was any change in diphtheria toxin expression status.      We report a cluster of NTTB C. diphtheriae cases in a skin clinic and evidence of onward household transmission. There was no evidence of reversion to diphtheria toxin expression in the isolates over the 80 month period studied. These data will help to inform updates to future guidance in the management of NTTBsuch cases and contacts in the UK.