Botulism – the Rare But Potentially Fatal Foodborne Illness

All my life I’ve been a little fearful of eating home-canned beans, because of the rare but potentially fatal illness caused by the Clostridium botulinum bacterium. The botulinum toxin produced by this bacterium is one of the most lethal natural toxins known to man. Now that my organic garden is overflowing with fresh beans, and I can’t possibly eat them all fresh, my mind has turned again to this microscopic organism, which lives naturally in the soil.

Eating poorly prepared food isn’t actually the only way you can be sickened by this type of bacteria. It is also possible for the bacterium to infect an open wound, (often caused when drug users share needles), and babies can sometimes be sickened by consuming the spores of the bacteria. Fortunately, the incidence of botulism poisoning is quite rare – only an average of 110 cases are reported in the United states each year. The majority of these cases, 72%, are infant botulism, and 25% are caused by eating contaminated food.

Infants can be infected by eating honey, corn syrup or other sweetener that contains dormant bacterial spores, so parents are warned to not give honey in any form to babies under one year old. Once the child begins to eat solid food, stomach acids will kill the bacterial spores and prevent them from growing.

As a gardener, it is the food-born illness that most concerns me, and the list of symptoms and side effects makes it reasonable to be concerned. Botulism is a paralytic illness, and the symptoms are very similar to those of people who are having a stroke. Symptoms can include difficulty swallowing, drooping eyelids, muscle weakness, and double or blurred vision. These symptoms can occur anywhere from 6 hours to 10 days after eating contaminated food. Patients treated for this illness can be on a ventilator for weeks, under intensive medical care. Paralysis will slowly improve over a number of weeks if the illness is diagnosed early enough. In the past, up to 1/2 of the people contracting the illness dies, but medical care has now reduced the fatality rate to 8%. Patients may continue to feel tired and have difficulty breathing for years after recovering from this illness.

Clostridium botulinum bacteria grow and multiply in oxygen-free environments that are high in moisture and low in acidity. This is an excellent description of the inside of a jar of low-acid vegetables. High levels of sugar can help reduce the production of the bacteria, and its toxins. The bacteria are killed when vegetables are canned under high heat and pressure, the way store-bought canned goods are processed.

My parents canned thousands of jars of beans over the years, but were always careful to follow the common practice of boiling the beans for at least 10 minutes before eating them. The Centers for Disease Control (CDC) agrees that this is a good idea. It also makes sense to use the most recent home canning advice from the US Department of Agriculture, since new methods are being developed all the time. It just pays to be safe if you can low-acid foods, like beans, asparagus, beets, and corn.

People have also been known to be sickened by botulinum bacterium growing in chopped garlic stored in oil, which should always be kept refrigerated, and in
potatoes baked in aluminum foil, if the potatoes are left in the foil and are not refrigerated.

Do frozen vegetables pose the same dangers as home-canned produce? According to the USDA Safe Food Handling Fact Sheet, “Food stored constantly at 0o F will always be safe. Freezing keeps food safe by slowing the movement of molecules, causing microbes to enter a dormant stage. Freezing preserves food for extended periods because it prevents the growth of microorganisms that cause both food spoilage and foodborne illness.”

However, the same document goes on to say that freezing does not kill bacteria – it simply puts it into dormancy. As soon as the food is thawed, the bacteria can begin to grow and multiply, just as they can in any food. To be safe, use up any thawed (and even fresh) veggies as soon as possible, and keep any left-overs in the fridge.