Botulism

Updated - September 2023

What are the causes?

The pathogen that causes botulism is a bacterium known as Clostridium botulinum (C. botulinum). C. botulinum bacteria develop in anaerobic conditions, in other words in the absence of oxygen. They multiply and produce toxins in food, and it is these extremely potent toxins that are responsible for botulism. Of the seven types of botulism known today, four (types A, B, E and more rarely F) affect humans. 

In foodborne botulism, the toxin is ingested directly via contaminated food. In infant botulism, resistant forms of the bacteria, spores, are ingested. C. botulinum then colonize the infant's intestines and release toxins, which cause illness. Infants are particularly at risk because their immune system is not yet mature. 

In rare cases, botulism can occur when spores get into a wound and bacteria then develop in anaerobic conditions. 

How does the disease spread?

Foodborne botulism in humans is caused by eating food that has been improperly stored in low oxygen conditions and has been contaminated by botulinum toxins. 

Infants under the age of one can contract infant botulism by ingesting C. botulinum spores. 

There is no human-to-human transmission. 

Quels sont les symptômes ?

Les symptômes diffèrent selon le type de botulisme. 

Les symptômes liés au botulisme alimentaire apparaissent généralement au bout de quelques jours : atteinte oculaire (défaut d’accommodation, vision floue), sécheresse de la bouche accompagnée d’un défaut de déglutition voire d’élocution, troubles digestifs et neurologiques. Dans les formes avancées, les symptômes évoluent vers une paralysie descendante des membres et des muscles respiratoires. C’est cette insuffisance respiratoire qui entraîne le décès.  

Le botulisme infantile est de gravité variable et se caractérise par des troubles digestifs, notamment la constipation de l’enfant. Celui-ci peut également être irritable, avoir des pleurs altérés, une perte de contrôle des mouvements de la tête.

How is the disease diagnosed?

Diagnosis begins with a clinical examination, but this is not enough to confirm botulism as symptoms can be confused with those of stroke or Guillain-Barré syndrome. So the clinical examination is followed by laboratory tests to confirm the presence of the toxin in the suspected food sample or to identify the bacteria in the patient's stools. 

What treatments are available?

Patients must be treated as soon as possible. An antitoxin may be administered.

If the patient's condition deteriorates, intensive respiratory therapy with mechanical ventilation may be required. The vast majority of patients treated immediately recover without any long-term effects, but treatment and convalescence may take several weeks or even months. 

Antibiotics can only be used for wound botulism. 

There is a vaccine against botulism, but it is only used for certain categories of people (for example military personnel) and it can cause severe side effects. 

How can botulism be prevented?

Prevention is based on observance of good hygiene practices when preparing and storing food to prevent the development of C. botulinum and production of the toxin. Foodborne botulism can be prevented by washing food and cooking it properly (toxins are destroyed by lengthy boiling), using clean water and storing food at the right temperature. 

As C. botulinum spores can be found in honey, it is recommended not to give honey to infants under one year old. 

How many people are affected?

In France, botulism is rare: the average incidence has stabilized at around ten outbreaks per year, each generally involving one to three individuals. Most outbreaks are foodborne botulism caused by consumption of home-canned food or sometimes also artisan or mass-produced products. Cases of infant and wound botulism are rarer.