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

The disease may manifest as (2):

  • an upper respiratory tract infection
    • characterised by membranous pharyngitis (known as a pseudo-membrane)
  • 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)
  • 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)


  • 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)


Last edited 04/2019 and last reviewed 03/2022