- Botulism is a rare but serious paralytic illness, caused by a toxin produced by bacteria.
- Botulism in adults can result from eating contaminated food or infection of a wound with botulism bacteria.
- Infant botulism is a type of botulism in which bacteria are ingested and produce the toxin in the digestive tract.
- Many of the symptoms of botulism are the result of muscle paralysis caused by the bacterial toxin.
- If untreated, death may occur, usually as a result of respiratory paralysis.
- reatment for botulism requires hospitalisation and often time in an intensive care unit.
- Avoiding contaminated foodstuffs is an important measure in the prevention of botulism.
Botulism is a rare but serious paralytic illness caused by a toxin produced by bacteria. This toxin prevents nerves from releasing the chemicals that transmit signals to other nerves.
There are three main kinds of botulism: food-borne botulism, from eating contaminated food; wound botulism from infected wounds; and infant botulism, from consuming bacterial spores.
All forms of botulism can be fatal and are considered medical emergencies.
Outbreaks of botulism related to sausages and other foods were noted in Europe in the 19th century, and sausage poisoning became notifiable. The Latin word for sausage is botulus, and thus the condition became known as botulism. The organism and its toxin were first identified in 1897.
The bacterium that causes botulism is called Clostridium botulinum. These rod-shaped organisms grow best in low-oxygen conditions. The bacteria form spores which allow them to survive in a dormant state until exposed to conditions that can support their growth. These spores can be found in soil and untreated water throughout the world.
The botulism bacteria can contaminate canned or improperly preserved food, where they produce the toxin. In adults, eating food that contains the botulism toxin causes food-borne botulism. When eaten, even minute amounts of this toxin can cause severe poisoning. The toxin is absorbed from the intestines and attaches to the nerves, causing the signs and symptoms of botulism. Most commonly contaminated foods are home-canned vegetables, cured pork and ham, and smoked or raw fish. The danger comes when eating contaminated food that has not been properly cooked or reheated after the toxin has been produced by the bacteria.
There are seven types of botulism toxin, designated by the letters A to G; only types A, B, E and F cause illness in humans. Although different strains of the organism can produce the different toxin types, a single strain will almost always produce only one type of toxin.
Wound botulism occurs if the spores contaminate open wounds and produce the toxin there.
Infant botulism is a special type of botulism in which living bacteria or their spores are ingested and grow within the infant's gastrointestinal tract and produce the toxin. Although infant botulism has been associated with the ingestion of contaminated honey, other sources of infection have been described (eg soil contamination).
Botulism is not spread from person to person.
Who gets it and who is at risk?
There are very few cases of botulism poisoning each year. In the United States, an average of 110 cases of botulism are reported annually. Of these, approximately 25% are food-borne, 72% are infant botulism, and the rest are wound botulism.
Outbreaks of food-borne botulism involving two or more people occur almost each year and are usually caused by eating contaminated home-canned foods. The number of cases of food-borne and infant botulism has not changed much in recent years, but wound botulism has increased because of the use of contaminated needles to inject illegal drugs.
Symptoms and signs
The early symptoms of botulism may include:
- Nausea and vomiting
- Abdominal pain or cramps
- Constipation or diarrhoea
- Dry mouth
Later symptoms include:
- Vision disturbance (double or blurred vision)
- Difficulty breathing or shortness of breath
- Drooping eyelids
- Impaired (slurred) speech
- Difficulty swallowing
- Progressive muscle weakness
- Poor reflexes
Wound botulism differs very little from the above, except the early symptoms may be absent. Fever is not a feature of botulism, unless a wound has become infected with other organisms as well.
In infants, symptoms of botulism include:
- Weakness and loss of muscle tone
- Weak cry
- Poor feeding and weak sucking
- Appears alert but weak and lethargic
- Difficulty breathing
- Visual disturbances
- Poor reflexes
Many of the above symptoms of food-borne and infant botulism are the result of the muscle paralysis caused by the bacterial toxin.
In food-borne botulism, symptoms generally begin 18 to 36 hours after eating contaminated food, but they can occur as early as six hours or as much as 10 days later. The incubation period for infant botulism is unknown.
The doctor will take a medical history and perform a physical examination. The presence of appropriate neurologic symptoms will suggest botulism, but these are usually not enough to allow a diagnosis. Other diseases such as Guillain-Barré syndrome, stroke and myasthenia gravis can appear similar to botulism, and special laboratory tests may be needed to exclude these other conditions. These tests may include:
- Tests of blood, stool and suspected food to identify the toxin, as well as culture of the stool to grow C. botulinum.
- The most direct way to confirm the diagnosis is to demonstrate the botulinum toxin in the patient's serum (the watery portion of blood) or stool by injecting serum or stool into mice and looking for signs of botulism.
- Tests may also include a brain scan, spinal fluid examination, nerve conduction test (electromyography, or EMG), and a tensilon test for myasthenia gravis.
Hospital care is recommended for all forms of botulism.
If diagnosed soon after symptoms begin, food-borne and wound botulism can be treated with an antitoxin that neutralises the action of the toxin circulating in the blood. (This must be done with care because of the risk of anaphylaxis, a severe form of allergic reaction which occurs in 10 – 20% of patients) The antitoxin can stop the patient from getting any worse, but recovery still takes many weeks. Doctors may try to remove contaminated food still in the gut by inducing vomiting or by using enemas. Wounds should be treated, usually surgically, to remove the source of the toxin-producing bacteria. In addition, some doctors treat the patient with antibiotics (eg penicillin) to kill the bacteria, although the value of this has not been proved.
Emergency hospitalisation is recommended if respiratory impairment is detected, and treatment for adults often requires time in an intensive care unit. Respiratory failure and paralysis that occur with severe botulism may require intubation (a tube inserted through the nose or mouth into the trachea to provide an airway for oxygen) and mechanical ventilation (a machine is used to assist breathing) for weeks, plus intensive medical and nursing care for several months. Intravenous fluids can be given while swallowing difficulties persist. Also, naso-gastric feeding (feeding through a tube inserted in the nose) should be initiated. After several weeks, the paralysis slowly improves.
Treatment for infants requires hospitalisation and possibly care in an intensive care unit. Currently, antitoxin is not routinely given for treatment of infant botulism.
Health care providers report occurrences of the disease to health authorities, so that contaminated food can be removed from stores. Botulism is a notifiable condition in South Africa, which means confirmed cases must be reported to the Department of Health.
If untreated, early symptoms of botulism may progress to cause paralysis of the arms, legs, trunk and respiratory muscles. Death occurs in 70% of untreated cases, usually as a result of paralysis of the respiratory muscles.
In the past 50 years the proportion of patients with botulism who die has fallen from about 50% to 8%, because of increasingly effective treatment. Respiratory failure can cause death in up to 10% of food-borne botulism cases and 2% of infant botulism cases. Prompt treatment significantly reduces the risk of death.
Other complications of botulism may include:
- Aspiration pneumonia and infection – which results when stomach contents or food is breathed into the lungs, because the normal reflex to prevent this is not present when muscles are paralysed.
- Infant botulism has been associated with sudden infant death syndrome (SIDS), or crib death.
- Patients who survive an episode of botulism poisoning may have fatigue and shortness of breath for years, and long-term therapy may be needed to aid recovery.
When to call the doctor
Go to the emergency centre at your hospital or call your local emergency number immediately if botulism is suspected.
Although there are very few cases of botulism poisoning each year, prevention is extremely important.
Bulging containers should not be opened and foods that smell off should not be eaten or even tasted. Commercial cans with bulging lids should be returned unopened to the vendor.
Food-borne botulism has often resulted from home-canned foods with low acid content, such as asparagus, green beans, beets and corn. However, outbreaks of botulism from more unusual sources such as chopped garlic in oil, chili peppers, tomatoes, improperly handled baked potatoes wrapped in aluminium foil, and home-canned or fermented fish have occurred.
To reduce contamination of foods, home canning and preserving of all non-acid foods (that is, all foods other than fruits and tomatoes) must be done according to strict hygienic recommendations to reduce the risk of contamination. For example, oils infused with garlic or herbs should be refrigerated. Potatoes that have been baked while wrapped in aluminium foil should be kept hot until served or refrigerated. In addition, because the botulism toxin is destroyed by sufficient heat, people who eat home-canned foods should consider boiling the food at 100 degrees Celsius for 10 minutes, or heating it at 80 degrees Celsius for 30 minutes before eating it to ensure safety.
Because honey can contain spores of Clostridium botulinum and this has been a source of infection for infants, children younger than 12 months old should not be fed honey. Honey is safe for children aged one year and older.
Wound botulism can be prevented by prompt medical care of infected wounds and by not using injectable illegal drugs.
Health authorities must investigate suspected outbreaks of botulism immediately, and if they involve a commercial product, the appropriate control measures should be put in place. Doctors should report suspected cases of botulism to a government health department.
Reviewed by Dr Andrew Whitelaw, MBBCh (Witwatersarnd), MSc (UCT), FCPath (Micro) (SA) Senior registrar, Department of Microbiology, University of Cape Town and Groote Schuur Hospital.