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Botulism

Epidemiology of Infectious Disease: Botulism

Causal agent
Botulism is caused by a neurotoxin produced by Clostridium botulinum1.
There are 7 neurotoxins (A-G); only types A, B, E and F cause illness in humans.

There are 3 naturally occurring forms of botulism:

    1.Food-borne botulism is a severe intoxication resulting from the ingestion of preformed toxin present in contaminated food1. Food-borne botulism is commonly associated with home preserved foods such as home canned fruit and vegetables with low acid content and smoked or preserved meats and fish.
    2.Wound botulism has the same symptoms as other forms of botulism but occurs when the organisms enter an open wound and are able to reproduce in an 'anaerobic' environment. Injecting drug users are the highest risk group for wound botulism2.
    3.Intestinal botulism occurs in infants and is extremely rare. It is caused by consuming the spores of the botulinium bacteria, which grow in the intestines and release toxin.

Inhalation botulism
In addition, a deliberate release may involve airborne dissemination of toxin4.

Common clinical features
Symmetrical descending flaccid paralysis with prominent bulbar palsies including diplopia, dysarthria, dysphonia and dysphagia4.

Afebrile and no change in sensory awarness4.

Gastrointestinal symptoms occur only in cases of food-borne and intestinal botulism. Common symptoms include nausea, vomiting and diarrhoea followed by constipation. Ingestion of large amounts of toxin may lead directly to neurological symptoms4.

With treatment the case fatality rate is 5-10% of cases.

Epidemiology

  • Naturally occurring botulism is extremely rare in the UK.
  • Between 1990 and 2005 there were 5 laboratory confirmed cases of Clostridium botulinium intoxication in England and Wales (Health Protection Agency).
  • An outbreak in 1989 due to hazelnut yogurt resulted in 26 cases of Clostridium botulinium (Health Protection Agency).
  • Wound botulism is the most common form of botulism in the UK. Between March 2000 and September 2002 there were 24 clinically diagnosed cases of wound botulism in the UK all cases occurred among injecting drug users4.

Reservoir
Spores ubiquitous in soil worldwide, are found in agricultural products including honey, marine sediment and in the intestinal tract of animals including fish3.

Mode of transmission
Ingestion of preformed toxin.
Introduction of spores into a wound.
Ingestion of spores rather than toxin1.

Incubation period
Food-borne - 12-72 hours with a range of 2 hours to 10 days.
Wound - 4-21 days.
Inhalational botulism - Intestinal botulism - unknown.

Period of Communicability
No person to person spread.

Treatment
Treatment is with trivalent equine antitoxin and must be given as early as possible following clinical diagnosis2.4. Recovery may take weeks to months.

Prevention and control

  • A vaccine against botulism exists but there is concern regarding its effectiveness and safety. In addition it has no effect in post-exposure treatment2,4.
  • The use of antibiotics post-exposure is not indicated4.
  • Care with commercial and home canning processes1.
  • Avoid consumption of food from containers that appear to bulge or are damaged1.
  • Boil home canned foods for 10 minutes.

References

    1.Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.
    2.Health Protection Agency Centre for Infections, Botulism Fact Sheet, January 2006.
    3.Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
    4.Health Protection Agency. Botulism, Interim Guidelines for Action in the Event of a Deliberate Release. Health Protection Agency Centre for Infections, January 2006. Available online at: http://www.hpa.org.uk/infections

© CM Kirwan 2006