What Is Botulism Poisoning?

Botulism is a food-borne illness caused by the Botulinum toxin produced by Clostridium botulinum, a spore-forming anaerobic bacteria. Botulism poisoning is rare but extremely serious, and it can be potentially fatal. Approximately 10 to 30 outbreaks are reported each year. This poison is extremely potent; it is widely considered the most potent biological toxin for humans. 1

The type of foods most frequently contaminated with Clostridium botulinum are low-acid canned foods. The bacteria thrives in anaerobic environments, so it is particularly at home in these sealed containers. The most frequent sources are canned foods such as:

Canned Corn
Asparagus
Peppers
Green Beans
Beets
Mushrooms
Ripe Olives
Soups
Chicken
Chicken Liver
Liver Pate
Luncheon Meats
Ham
Sausage
Smoked and Salted Fish
Uneviscerated Fish 2 3

The germination of the bacterial spores in foods is enhanced when the pH is greater than 4.5 and the salt concentration is less than 3.5%. 4 This does not mean, however, that highly acidic or highly salted foods cannot be contaminated.

home canned foods — Home canned foods are often the source of botulism

There have been some high-acid foods that have been involved in botulism poisoning, such as tomatoes, pears, and apricots. In these cases, it is thought that the foods must have been previously contaminated with another organism, such as mold, yeast, or bacteria, and that this organism grew and raised the pH of the food to below 4.5 so that Clostridium botulinum could grow. 5

Home Canned Peppers Contaminated with Botulinum

Nitrite also greatly retards the growth of Clostridium botulinum, and cured meats are a major concern for botulism. The addition of nitrites to cured meats helps mitigate this danger, and currently, no protection from botulinum is known to be better than nitrites. There are concerns about the health effects of added nitrites in foods, such as it being a carcinogen.

However, the risk of botulism may be greater than the risk of nitrite, and the amount of nitrite added to the diet, when a moderate amount of cured meats is consumed, is much less than the amount of nitrite produced by bacteria in the mouth and swallowed with saliva. Since 1990 over 90% of cured meats have contained less than 50 ppm of nitrate and only 0.1% contain more than 200 ppm. 6

The bacteria is found in soil and water. Seafood is a more common source than animal meats. Home-canned vegetables and fruits of low acidity are a much more common source than commercially canned products. Sometimes the poison can come from less expected places, like canned tomato products or from baked potatoes wrapped in aluminum foil that are not kept hot. The bacteria can only release its toxins into the food if it can grow in an oxygen-free environment.

The bacteria can sometimes exist in a hibernating form on the surface of potatoes, and baked potatoes can therefore be a source of the contaminant. The temperatures required to bake potatoes would not destroy the bacteria. Still, they should pose no hazard for adults if consumed immediately.

However, if potatoes harboring the bacteria are wrapped in foil, baked, and then allowed to sit out and cool for long enough, the bacteria can become active and find itself in an oxygen-free environment. If these potatoes are then eaten, poisoning can occur. One should never eat baked potatoes that have been wrapped in foil and then allowed to set for a long time. 7 8

Dented cans like these should raise concern about potential botulism.
Photo by Debora Cartagena

Honey can harbor botulism spores. In studies of honey, up to 13% of the test samples contained low numbers of C. botulinum spores, although usually not the toxin itself.

Do not give honey to infants. As will be explained below, botulism spores themselves are relatively non-harmful to healthy adults, but can be dangerous for children. In adults, the poisoning occurs as a result of ingesting the protein toxins produced by the botulism bacteria; in children, it can occur from the spores themselves, which are able to germinate in their underdeveloped colons.

By far the most frequent cause of botulism is improperly home-canned food, especially food with low acid content. To avoid this toxin, home canners should educate themselves and use proper methods for canning low-acid foods.

Visit the National Center for Home Food Preservation for up-to-date and safe procedures for canning most types of food, as well as other home preservation methods.

Avoid commercially canned foods with leaky seals or with bent, bulging, or broken cans. Refrigerate oils containing garlic or herbs since bacterial spores may have been introduced into the oil. Refrigeration retards the growth of the bacteria. 7

There have been cases of botulism poisoning from commercially prepared foods, including potato salad, cheese sauces, and chopped garlic. 9

Others include:

Potato Soup (2011)
Clam Chowder
Bean Dip
Chili Sauce (2007)
Beef Stew
Hash
Corned Beef Hash
Barbecue Pork
Barbecue Beef
Chip Beef
Brunswick Stew
Sausage Gravy 10

Most of the commercially prepared foods identified as botulism vehicles were low-salt, preservative-free products packaged in air-tight containers, having no barrier against C. botulism spore germination besides refrigeration, which by itself frequently fails.

A frequently stated myth is that since the botulinum bacterium cannot be destroyed by cooking, or that it cannot be killed by “ordinary heating” (must be heated up to 250 degrees), cooking cannot protect you from poisoning. This is not true.

Although the bacteria spores are very heat-resistant and require a great deal of heat to kill, the toxin itself is heat-sensitive and is readily destroyed by heat, although the exact heat and exposure needed is variously reported. The CDC suggests that heating to an internal temperature of 85 degrees C (185 degrees F) for at least 5 minutes should be sufficient to inactivate the toxin in contaminated food or drink. Once the toxin is destroyed, the bacterial spores are generally of little concern to healthy adults because they are unable to germinate in the gut due to the competing microflora. 5 11

Toxicity and Mechanisms

Botulinum toxin is among the most deadly substances in the world. It is seven million times more toxic than cobra venom. The toxin works by blocking the action of acetylcholine, an important neurotransmitter, by binding to cholinergic nerve terminals and preventing acetylcholine from being released. Contaminated food containing as little as 0.05 µg (micrograms) of the toxin can be fatal. 12 4

The toxin affects the nerves involved in the body’s autonomic functions, such as those controlling breathing, dilation of blood vessels, and heart function. 5

Sausage Poisoning

The earliest known cases of botulism poisoning occurred in Germany from sausage consumption. In fact, in the early 1800s, this type of food poisoning was known as sausage poisoning, and the term botulism is derived from the Latin term botulus for “sausage.” Justinus Kerner, a medical officer for the German town of Wurttemberg, encountered many cases of people who had died after having difficulty breathing, speaking, and swallowing. Almost all of these people had eaten sausages that were not properly prepared (inadequately cooked).

Kerner managed to extract a substance from sausage that he thought might be causing the poisonings. He even injected himself with the poison and experienced many of the same symptoms — thankfully surviving — and subsequently wrote the first detailed report on wurstgift, the aforementioned sausage poisoning. It later became known as Kerner’s Disease.

Although botulism occurrences have never been a regular thing, and large-scale epidemics do not occur, there have been numerous significant outbreaks through the years, many involving infants, who are much more susceptible to the disease.

An unusual cause of botulism poisoning began to occur in New York City in 1982 in heroin users. The poisonings were seen in injection users who injected a type of heroin called Black Tar Heroin, so called because of its dark, gummy appearance. Although this began in New York, most cases since have been in California. It is relatively rare, and few deaths have occurred. 7

Types of Botulism

Seven different types of botulism neurotoxins are recognized, and named types A through G. There are three main types of botulism poisoning and two more rare types. The first three below are the main types, followed by two other, rarer types.

Foodborne botulism (ingestion of preformed toxin)
Infant botulism (production of toxin in vivo in immature infant gut)
Wound botulism (contamination of wounds)
Adult infectious botulism (production of toxin in vivo in adult gut after frequent abdominal surgery, achlorhydia, Crohn’s disease, or recent antibiotic treatment)
Inadvertent botulism (after intramuscular injections of botulinum toxin for other medical or cosmetic purpose) 13 10

Foodborne botulism is the most common type and has been discussed throughout this article. This occurs when the bacterial spores have been able to germinate in contaminated foods and thus produce toxin which is then ingested to cause poisoning in victims. In this case, it is the presence of the toxin that causes the disease, not the bacteria itself. The healthy adult gut, which has a population of friendly microflora, prevents the botulinum bacteria from germinating, thus eliminating any danger of ingesting the actual bacterial spores.

However, in infants, who do not have a well-developed microflora population, the ingestion of botulism spores can be highly dangerous (do not give infants honey). This type of botulism, called infant botulism, most often occurs in children younger than 6 months. Honey is the most common source.

Intestinal colonization of botulism spores and subsequent poisoning in adults can also occur, but is very rare and usually requires the ingestion of large numbers of bacteria. This is known as adult infectious botulism but the disease is not spread from person to person.

Wound botulism happens when contaminated soils get into open wounds. This tends to occur most often in young boys. The symptoms are the same. Fewer than 5% of all cases are wound botulism. 4

Botulism from 1990 to 2000

According to surveillance data and reports reviewed by the CDC, between 1990 and 2000, there were 160 incidences of botulism in the United States, with 263 individual cases. Fifty-eight of these events occurred in Alaska, totaling 103 (39%) cases. The case-fatality rate was 4% and the median number of cases per event was 1 (range 1–17).

Toxin type A caused 51% of all cases; toxin type E caused 90% of Alaska cases. A particular food was implicated in 126 (79%) events. In the lower 49 states, a noncommercial food item was implicated in 70 (91%) events, most commonly, home-canned vegetables (44%). Two restaurant-associated outbreaks affected 25 persons. All Alaska cases were attributable to traditional Alaska Native foods.

Although the traditional fermentation practices of native Alaskans may have made botulism a problem throughout history, modern alterations may have exacerbated the problem, such as using plastic or glass containers, which create an airtight environment in which the bacteria can thrive. After Alaska, the next highest incidence rates were in Idaho and Washington.

With all events, as with previous years, home-canned foods were the leading vehicle for poisoning, along with other home-prepared or home-preserved foods. Restaurant-prepared foods account for only a few events. 10

Antitoxin

A supply of antitoxin against infant botulism is maintained by the California Department of Public Health’s Infant Botulism Treatment and Prevention Program. The CDC maintains a supply of antitoxin against other kinds of botulism as part of its Strategic National Stockpile. State and local health departments may also maintain supplies.

These are trivalent botulinum antitoxin. They contain three antibodies for the toxins that are produced by different types of C. botulinum bacteria: A, B, and E, which are the three most common types. These antitoxins are most effective when given early on during the disease. The botulism antidote used for adults is different from that used for babies. A new type of treatment was developed for infants in the late 1990s because the treatment used for adults seemed to make babies sicker. This new infant antitoxin was tested and proven safer and more effective. 13 14

Symptoms

Symptoms of botulism poisoning begin as early as 6 to 10 hours after eating contaminated food, but most often after 12 to 36 hours.

Initial Symptoms

Abdominal cramps
Nausea
Vomiting
Blurred vision

Later Symptoms

Constipation
Double vision (diplopia)
Drooping eyelids
Slurred speech
Difficulty swallowing
Dry mouth
Muscle weakness (moving down the body)
Paralysis of breathing muscles (ventilation is required)
Inability to urinate

Infant Symptoms

Constipation
Poor feeding
Respiratory distress
A weak cry
Weakness, loss of muscle tone, “floppiness”, unable to support head3,9

Clinical Signs

Absent or decreased deep tendon reflexes
Absent or decreased gag reflex
Urine retention (inability to urinate)
Loss of muscle function and feeling
15 4 7

Botulism Treatment

Doctors are urged to administer antitoxin to patients who show even the slightest signs of botulism poising, as the earlier the antidote is given, the better the outcome. The antitoxins stop the action of the toxin so that further damage does not occur.

If it is suspected that any of the contaminated food is still in the stomach, vomiting might be induced. If there is breathing difficulty, mechanical ventilation may be required. A breathing tube may need to be inserted through the windpipe to provide an airway so that oxygen can be delivered via a breathing machine.

If unable to drink due to difficulty swallowing, intravenous fluids may be given. Also, a feeding tube may be needed. Antibiotics are also sometimes given, but they do not always do anything, since they have no action against the toxin. Antibiotics should not be given in cases of infant botulism, as these tend to make babies sicker (cause unknown).

Prompt medical attention and supportive care can often prevent death, and even those who have reached late stages of the disease, such as the inability to breathe, can survive when proper hospital care is given. Prolonged symptoms may remain in survivors. 16 13

Type A is generally considered to have a less certain prognosis than type E. With type E, even after symptoms have developed, if antitoxin is given, the patient will usually recover. The administration of antitoxin is thought to have less effect on type A. 5

All botulism cases should be reported to local or state health departments or the U.S. Centers for Disease Control and Prevention.