The screenshot of the news article below says it all. I have never seen a case of diphtheria in my career and hence needed to do a little reading up.
Respiratory diphtheria is a clinical syndrome characterized by sore throat and fever (the initial presentation is identical to most viral upper respiratory tract infections), followed rapidly in severe cases by the formation of a greyish pseudomembrane most commonly at the tonsils and/or pharynx. In the severe form of disease, the combination of swollen cervical lymph nodes and inflamed mucosa results in a “bull neck” appearance in the patient, and death occurs as a result of suffocation caused by the pseudomembrane, or less commonly from the concomitant cardiac damage (myocarditis) that occurs in a proportion of patients.
The other form of diphtheria is cutaneous diphtheria, which is classically described as punched out, non-healing skin ulcers covered by a grey membrane and exuding a sweetish-putrid scent.
Both of these conditions are caused by Corynebacterium species – most commonly C. diphtheriae, but also C. ulcerans (especially cutaneous diphtheria) and C. pseudotuberculosis – that produce the extracellular diphtheria toxin. Not all strains of C. diphtheriae are toxigenic and produce the toxin – interestingly, the gene for the toxin (tox) is carried on a lysogenic bacteriophage that can infect all three Corynebacterium spp. mentioned above, although isolates have been found where the tox gene was present without any flanking prophage regions. There is an excellent if very technical review of the diphtheria toxin here.
The bacteria are spread via droplets (sneezing or coughing) and also by contact. Interestingly, it is believed that cutaneous diphtheria may be even more contagious than respiratory diphtheria.
The diphtheria vaccine is a highly effective and safe toxoid vaccine (i.e. a toxin that has been rendered harmless but nonetheless remains able to elicit an immune response) that was independently developed by French veterinarian Gaston Ramon and British immunologist Alexander Glenny in the early 1920s. It is currently combined with different toxoid vaccines (tetanus and/or pertussis) and recommended by the World Health Organization’s (WHO’s) Expanded Program on Immunization since its inception in 1974. Diptheria rates have fallen worldwide with increasing adoption of the vaccine – the WHO reported 97,164 cases worldwide in 1980, and 7,097 cases in 2016 (although the 2015 and 2016 data are curious because Madagascar reported several thousand cases both years after a prolonged period where only a handful of cases were reported).
The vaccine was available in Singapore from 1938, and made mandatory by law for children below 7 years of age in 1962. Uptake of vaccines on the National Childhood Immunisation Programme is very high in Singapore. For example, an estimated 96.8% of all children in Singapore receiving the diphtheria, tetanus and pertussis vaccination in 2013. Therefore, there is considerable herd immunity among the local-born population, which was borne out by a Ministry of Health national serological study in 2010.
In that study, residual sera from 3,293 adults (age 18-79 years) that had participated in the National Health Survey were tested for IgG antibodies to diphtheria and tetanus, with the finding that 92.0% of those tested had at least basic protection against diphtheria. As with the case in other parts of the world, the authors noted that seroprevalence declined with age, with the most marked drop occurring for diphtheria in those in the age 50-59 years bracket.
The last case of diphtheria (prior to this current unfortunate Bangladeshi construction worker) was reported in Singapore in 1992, but as can be seen from the screenshot of the WHO diphtheria page for Singapore below, the disease had already become very rare since before the 1980s.