Corynebacterium diphtheriae

Last edited 11/2022 and last reviewed 02/2023

Diphtheria is an acute infectious disease caused by the action of diphtheria toxin produced by toxigenic Corynebacterium diphtheriae or by Corynebacterium ulcerans (1).

Classical respiratory diphtheria is characterised by the insidious onset of membranous pharyngitis with fever, enlarged anterior cervical lymph nodes, and oedema of the surrounding soft tissue, giving rise to the "bull neck" appearance

  • although not always present, the membrane is typically grey, thick, fibrinous, and firmly adherent

The disease may manifest as (2):

  • an upper respiratory tract infection
    • characterised by membranous pharyngitis (known as a pseudo-membrane)
    • laryngeal diphtheria is characterised by gradually increasing hoarseness and stridor and most commonly occurs as an extension of pharyngeal involvement in children (4)
    • nasal diphtheria, usually mild and chronic, is marked by unilateral or bilateral nasal discharge, which is initially clear and later becomes bloody (4)

  • a cutaneous infection
    • occurs mainly in people who live in tropics
    • in industrialised countries it is reported in disadvantaged populations such as alcoholics, intravenous drug users and the homeless (1)
    • usually appears on exposed limbs, particularly the legs
      • lesions start as vesicles and quickly form small, clearly demarcated and sometimes multiple, ulcers that may be difficult to distinguish from impetigo (4)
      • classic description of diphtheritic lesions is that they are usually covered with an eschar, a hard bluish-grey membrane that is slightly raised. Individuals may have both respiratory and cutaneous symptoms (4)
  • an asymptomatic carrier state
    • may occur during the incubation period of diphtheria, during convalescence, or in healthy people (3)

Diphtheria is rare in the UK as a result of immunisation, but is still an important cause of disease in the developing world. It is quite common in South Africa and Russia. In the developed world a careful immunisation history must be taken

  • milder infections (without toxin production) resemble streptococcal pharyngitis and the pseudo-membrane may not develop, particularly in vaccinated individual
  • carriers may be asymptomatic
  • diphtheria toxin affects the myocardium, nervous and adrenal tissues, causing paralysis and cardiac failure

In countries where hygiene is poor, cutaneous diphtheria is the predominant clinical manifestation and source of infection. The normal reservoir of C. ulcerans is cattle. Infections in humans are associated with the consumption of raw dairy products and contact with animals. Person-to-person spread cannot be ruled out, although it is probably uncommon

Diphtheria is a notifiable disease in the UK (1)

Diphtheria is no longer easily diagnosed on clinical grounds as classic respiratory diphtheria is now rare in the UK due to the success of the routine immunisation programme. (4)

  • however, when healthcare systems are disrupted and vaccine coverage declines, diphtheria is one of the first of the vaccine preventable diseases to emerge as was the case in the former Soviet Union in the 1990s and, more recently, in camps of displaced Myanmar nationals in Bangladesh
  • mild respiratory cases of the disease resemble streptococcal pharyngitis and the classical pseudomembrane of the pharynx may not develop, particularly in people who have been vaccinated
  • with vaccine coverage for the routine childhood vaccination programme having been maintained at around 95% for the last 2 decades, the majority of cases within the UK now are mild infections in partially immunised individuals, or in adults that have been fully immunised but have waning immunity
  • infections may still occur in fully vaccinated individuals as the diphtheria toxoid vaccine prevents the clinical manifestations of toxigenic strains but does not prevent acquisition of carriage

Notes:

  • there is little likelihood of developing natural immunity from sub-clinical infection acquired in the UK. Based on sero-surveillance studies, approximately 50% of UK adults over 30 years are susceptible to diphtheria. The proportion susceptible increases to over 70% in older age cohorts
    • high immunisation uptake must be maintained in order to prevent the resurgence of disease which could follow the introduction of cases or carriers of toxigenic strains from overseas (1)

Reference:

Related pages:

clinical features

organism properties

transmission

diagnosis

management

complications

Schick test

diphtheria vaccination

Corynebacterium

diphtheroids