Diphtheria is an acute bacterial infection caused by toxigenic strains of Corynebacterium diphtheriae, a gram-positive bacillus. The dangerous effects are mainly due to diphtheria toxin. It can affect the upper respiratory tract or the skin. It is a serious infection with a mortality of around 5-10%.
It is spread through respiratory droplets, close contact with infected people and contact with infected skin lesions. The incubation period is 2-5 days.
Vaccination
The diphtheria vaccine is a toxoid vaccine that protects against the diphtheria toxin, rather than the bacteria. It is given as part of the routine UK vaccination schedule, in combination vaccines:
- 6-in-1 vaccine at ages 8, 12 and 16 weeks, and 18 months
- 4-in-1 vaccine at age 3 years and 4 months
- 3-in-1 vaccine at age 14 years
Presentation
Respiratory diphtheria presents with:
- Sore throat
- Low-grade fever
- Swollen cervical lymph nodes
- Dysphagia (difficulty swallowing)
- Shortness of breath in severe cases
The classic finding is a thick grey-white pseudomembrane over the tonsils or pharynx. This is made of dead epithelial cells, fibrin, white blood cells and bacteria. It may bleed if removed.
The characteristic appearance in severe illness is described as a “bull neck”, caused by marked cervical lymphadenopathy and soft-tissue swelling.
Cutaneous diphtheria presents with a chronic, non-healing skin ulcer, often with a grey membrane. It is usually less systemically severe than respiratory disease.
Treatment
Diphtheria is a notifiable disease, and the UK Health Security Agency (UKHSA) must be notified of all suspected and confirmed cases.
The diagnosis can be confirmed by swabs for bacterial culture taken from the throat, nose, or skin lesions. Samples can be tested for toxin production.
Treatment involves:
- Diphtheria antitoxin to neutralise the circulating toxin
- Antibiotics, usually with macrolides (e.g., clarithromycin, azithromycin or erythromycin) or penicillin
Patients need to be isolated, and anyone in contact requires personal protective equipment. Swabs are collected, and prophylactic antibiotics (e.g., clarithromycin) are given to close contacts and asymptomatic carriers (guided by public health advice).
Cutaneous diphtheria is treated with antibiotics. The antitoxin is usually not required unless there is systemic toxicity or respiratory involvement.
Complications
Diphtheria toxin can spread systemically and cause:
- Myocarditis
- Arrhythmias
- Heart failure
- Cranial nerve palsies
- Peripheral neuropathy
- Airway obstruction
- Death
Last updated May 2026
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