From black olives in water to homemade preserves: where botulism strikes

In Italy, "the home-produced foods most responsible for cases of botulism are black olives in water, canned mushrooms in oil, canned turnip tops, canned meat and fish (especially tuna)."

The Istituto Superiore di Sanità (National Institute of Health) provides the update on its website page dedicated to botulism, a neuro-paralytic disease caused by clostridial toxins (Clostridium botulinum, the best known of the clostridia that produce botulinum toxin).

Foodborne botulism can affect people of all ages and is not transmittable from person to person, experts point out. Symptoms typically appear within a few hours to over a week after consuming contaminated food (6 hours, 15 days). However, in cases of foodborne botulism occurring in Italy , symptoms typically appear within 24 to 72 hours after consuming the contaminated food. Obviously, the earlier the symptoms appear, the more severe the illness will be.

First in Sardinia, now in Calabria, several cases of possible foodborne botulism have been reported in Italy in recent weeks. Symptoms can range from mild, self-resolving cases to very severe, potentially fatal cases.

The most common symptoms are: blurred or double vision; dilated pupils; difficulty keeping the eyelids open; slurred speech; difficulty swallowing; dry mouth and throat; and constipation.

In the most severe forms, respiratory failure occurs, which can be fatal due to blockage of nerve conduction in the muscles responsible for respiration. The symptoms are clear: botulism has a symmetrical progression (it affects both the right and left hemispheres of the body) and a descending progression (from the head, to the neck, to the chest, up to paralysis of the limbs) and manifests as flaccid paralysis.

Since the spores of botulinum toxin-producing clostridia are ubiquitous, they can also contaminate foods and raw materials. However, not all foods are at risk of botulism . A food product—warns the ISS—is at risk of botulism if the spores of botulinum toxin-producing clostridia can find the conditions for germination and vegetative development within it.

Botulinum toxins are produced during the multiplication of the microorganism. Since one of the essential conditions for spores to develop is the absence of oxygen, fresh foods (salad, bread, pasta) are not at risk of botulism. However, canned and semi-canned foods that are not acidic or have not undergone acidification/fermentation treatments are at risk .

Industrially produced canned foods are generally not dangerous because the production technologies are well standardized and allow for the control of the development and toxigenicity of clostridia that produce botulinum toxin. Home- made canned foods are more dangerous because they are often made following recipes passed down over time and revised to reduce the amount of protective agents (primarily vinegar and salt), without any scientific basis.

To make safe vegetable preserves at home, "you need to cook the vegetables in a solution containing equal parts water and vinegar, jar the vegetables, add oil if necessary, and pasteurize after sealing the jar. Pasteurization is a heat treatment that can be done at home by completely immersing the filled, hermetically sealed jar in water, which is then brought to a boil for a time proportional to the size of the jar. For 350-400 g jars, 15-20 minutes of treatment may be sufficient," advise the ISS experts.

" Jams and preserves should instead be made using equal parts fruit and sugar. If the amount of sugar is reduced, lemon juice should be added in sufficient quantities to make the fruit acidic enough (pH less than 4.6) to block the growth of clostridia that produce botulinum toxin. To be safe , olives and other pickled products should be prepared using 100 g of salt per liter of water," the experts continue.

" Homemade canned meat or fish should be avoided . These products cannot be acidified or treated with quantities of salt or sugar sufficient to block the development and toxigenesis of clostridia that produce botulinum toxin. Their safety depends on the destruction of any spores present, applying a thermal process called sterilization. This process is carried out with superheated steam at a temperature of 121 degrees Celsius and a pressure of 2 atmospheres and cannot be conducted with the tools normally found in home kitchens," concludes the ISS.