What is botulism and how can you prevent it?

Botulism is a disease caused by the action of a toxin produced by Clostridia bacteria, in particular Clostridium botulinum. Found almost everywhere in the environment, this bacterium is responsible for rare but severe cases of food poisoning in humans. The foods most often involved in human cases include canned foods as well as home-made and artisanal cured meat and fish.

What is botulism?

Botulism is a disease caused by the action of a toxin produced by bacteria, in particular Clostridium botulinum. This bacterium is found everywhere in the environment – soil, dust, marine and freshwater sediments, contaminated water, slurry, etc. – in the form of highly resistant spores. In humans, botulism is a rare disease, but it can prove fatal in less than 5% of cases in France. 

Botulism can also affect animals, primarily cattle and farmed and wild birds.

How can you get botulism?

In humans, there are several forms of botulism that differ depending on the mode of contamination. The two most common forms in humans are: 

  • Foodborne botulism (botulinum poisoning), which is caused by the ingestion of botulinum toxin produced by the bacterium in food. This is the most common form in adults.
  • Infant botulism (intestinal toxaemia botulism) caused by the ingestion of Clostridium botulinum bacteria and/or spores. This form occurs in children under 12 months of age because their intestinal flora is not fully formed or fully functional.

There are also other forms of botulism, although they are much less common:

  • Adult intestinal botulism, which is similar to infant botulism but occurs in adults with an imbalanced microbiota (for example, after intestinal surgery or prolonged use of antibiotics),
  • Wound botulism, which occurs when Clostridium botulinum spores get into a deep wound, for example in drug addicts who use needles contaminated by the bacterium,
  • Iatrogenic botulism linked to an overdose of toxin during medical or cosmetic treatment (e.g. with Botox injections),
  • Inhalation botulism.

Botulism cannot be transmitted between individuals in any of these cases.

What foods are involved?

Low levels of C. botulinum spores are found in a wide variety of foods. The presence of botulinum toxin in low-acid processed foods is often due to a failure to control the sterilisation or curing process and/or to a break in the cold chain

The vast majority of the foods that cause botulism are home-made/artisanal products. In France, the foods most commonly involved in cases of botulism are:

  • dried cured meat and fish (cured ham),
  • canned vegetables (asparagus, green beans, carrots and carrot juice, peppers, Greek-style olives, pumpkin, tapenade, etc.), meat (terrine, pâté), ready-to-eat meals, and vacuum-packed salted and dried fish.

Honey contaminated by Clostridium botulinum spores has already been reported as being involved in cases of infant botulism, in particular in the United States.

Are certain population groups more susceptible to botulism?

Any individual could potentially develop botulinum poisoning after ingesting the toxin produced in a food.

Because their intestinal flora is not fully formed or fully functional, infants under the age of 12 months are prone to intestinal toxaemia botulism. This form is rare in France, but it is the most common form of botulism in the United States.

What are the health effects?

Botulism is a disease with an incubation period ranging from a few hours, usually 12 to 48 hours, to eight days.

The severity of symptoms depends in particular on the amount of botulinum toxin absorbed. They include:

  • digestive problems: vomiting, diarrhoea, constipation
  • ocular impairment: blurred or double vision, dilated or fixed pupils
  • dry mouth, difficulty swallowing and speaking
  • for the most severe forms, flaccid paralysis of the limbs and respiratory muscles, which can lead to death in less than 5% of cases in France.

The symptoms can last from a few days to several months.

How can you prevent it?

To avoid becoming ill, here are a few rules to follow:

  • Carefully prepare any food intended to be canned: clean fresh produce, comply with hygiene rules when slaughtering animals on the farm and preparing meat, and clean the containers and packaging used;
  • Follow the sterilisation instructions given by steriliser manufacturers, in terms of temperature/time and the number of canned units per steriliser. Note that boiling is not sufficient to sterilise food, as Clostridium botulinum spores are resistant even to boiling water.
  • Do not eat food from dented or bulging cans, or food that smells suspicious when opened. When opening glass jars, you should hear a popping sound caused by air intake. If this is not the case, you should discard the product.
  • For home-made ham, you must use the correct salt concentration in the brine, and brine the ham for a sufficient amount of time to enable the salt and nitrite that inhibit the growth of C. botulinum to reach the centre.
  • Compliance with the cold chain is essential for cooked but non-sterilised products that need to be kept cold: ready-to-eat meals, pâté, etc.
  • For commercial food, you must follow the cold storage instructions and comply with the use-by dates.
  • Do not feed honey to infants under 12 months of age.

What is ANSES doing about botulism?

  • Research mission:
    • developing and validating detection, typing and sequencing methods and characterising botulism strains as part of its reference mandate;
    • collecting data on animal botulism outbreaks and studying reservoirs and routes of contamination;
    • taking part in the investigation of animal botulism outbreaks in conjunction with managers and professionals in the field;
    • studying host/pathogen interactions and control methods with a view to controlling and preventing outbreaks of botulism.
  • Risk assessment mission: carrying out risk assessment work and issuing recommendations to prevent animal botulism outbreaks and control the Clostridium botulinum bacterium in food.
  • ANSES’s Ploufragan-Plouzané-Niort Laboratory has been the National Reference Laboratory for avian botulism since 2011.