Canned Food

Lore & Background

The most common cause of food-borne botulism is toxin produced by the bacterium in containers of food that have been improperly preserved. Fish that has been pickled without the salinity or acidity of brine that contains acetic acid and high sodium levels, as well as smoked fish stored at too high a temperature, presents a risk, as does improperly canned food. Food-borne botulism results from contaminated food in which *C. botulinum* spores have been allowed to germinate in low-oxygen conditions. This typically occurs in improperly prepared home-canned food substances and fermented dishes without adequate salt or acidity. Given that multiple people often consume food from the same source, it is common for more than a single person to be affected simultaneously. Symptoms usually appear 12–36 hours after eating, but can also appear within 6 hours to 10 days.

In Their Own Story

The muscle weakness of botulism characteristically starts in the muscles supplied by the cranial nerves—a group of twelve nerves that control eye movements, the facial muscles and the muscles controlling chewing and swallowing. Double vision, drooping of both eyelids, loss of facial expression and swallowing problems may therefore occur. The weakness then spreads to the arms (starting in the shoulders and proceeding to the forearms) and legs (again from the thighs down to the feet). Severe botulism leads to reduced movement of the muscles of respiration, and hence problems with gas exchange. This may be experienced as dyspnea (difficulty breathing), but when severe can lead to respiratory failure, due to the buildup of unexhaled carbon dioxide and its resultant depressant effect on the brain. Death occurs in 5 to 10% of people. In the past 50 years, the proportion of patients with botulism who die has fallen from about 50% to 7% due to improved supportive care.

Reader's Guide

Prevention is primarily by proper food preparation. The toxin, though not the spores, is destroyed by heating it to more than 85 °C (185 °F) for longer than five minutes. The clostridial spores can be destroyed in an autoclave with moist heat (120°C/250°F for at least 15 minutes) or dry heat (160°C/320°F for 2 hours) or by irradiation. The spores of group I strains are inactivated by heating at 121°C (250°F) for 3 minutes during commercial canning. Spores of group II strains are less heat-resistant, and they are often damaged by 90°C (194°F) for 10 minutes, 85°C for 52 minutes, or 80°C for 270 minutes; however, these treatments may not be sufficient in some foods. Treatment is with an antitoxin. In those who lose their ability to breathe on their own, mechanical ventilation may be necessary for months. Antibiotics may be used for wound botulism.

Did You Know?

• The word 'botulism' is from Latin *botulus*, meaning 'sausage'.
• About one microgram of botulinum toxin is lethal to humans when inhaled.
• Honey can contain *C. botulinum* spores and should not be fed to children under 12 months.
• Infant botulism was first recognized in 1976 and is the most common form of botulism in the United States.
• The toxin is destroyed by heating to more than 85°C (185°F) for longer than five minutes, but the spores are not.