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Epidemiology of Infectious Diseases: Diphtheria

Causal agent
Corynebacterium diphtheriae of which there are two main forms, respiratory and cutaneous (affecting the skin).

C. diphtheriae has 3 biotypes - gravis, intermedius, and mitis. The most serious disease is associated with gravis but any strain may produce toxin.

Common clinical features

  • Symptoms range from a moderately sore throat to toxic life-threatening diphtheria of the larynx or of the lower and upper respiratory tracts.
  • Disease can involve almost any mucous membrane. For clinical purposes, it is convenient to classify diphtheria into a number of manifestations, depending on the site of disease1;

Anterior nasal diphtheria
Pharyngeal and tonsillar diphtheria
Laryngeal diphtheria
Cutaneous (skin) diphtheria.

  • Cutaneous diphtheria is usually mild, typically consisting of sores or shallow ulcers and only rarely involving toxic complications.


  • Endemic worldwide.
  • A resurgence of diphtheria in the former Soviet Union occurred in the 1980s followed by a large epidemic from 1990. The epidemic spread throughout all the newly independent states, and peaked in 1994-5. Between 1990 and 1998, more than 157,000 cases and 5000 deaths were reported in the region4.
  • Before the introduction of mass immunization in 1942 diphtheria was common in the UK with around 60,000 cases and 4,000 deaths reported each year2.
  • In 2005 9 cases were notified in England and Wales.
  • The overall case fatality rate is 5-10% with higher death rates (up to 20%) among children under 5 years old and adults aged over 40 years1.


Mode of transmission
Airborne droplets or direct contact with infected respiratory discharges or skin ulcers.

Incubation period
2-5 days.

Period of Communicability

  • Untreated cases remain infectious for up to 4 weeks, after 3 days of antibiotic treatment cases are no longer infectious.
  • Rare chronic carriers may shed organism for 6 months or more1.

Prevention and control
Immunisation with diphtheria toxoid.  


  1. National Immunization Program, Centers for Disease Control and Prevention, Epidemiology and Prevention of Vaccine-Preventable Disease 'The Pink Book', 9th edition, U.S. Department of Health and Human Services, 2006.  Available at
  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association, 2004.
  2. Health Protection Agency (HPA), Diphtheria fact sheet.
  3. Salisbury DM, Begg NT.  Immunisation against infectious disease (The green Book). London: HMSO, 1996. Available at

© CM Kirwan 2006