Botulism is neuromuscular poisoning due to Clostridium botulinum toxin. Botulism may occur without infection if toxin is ingested. Symptoms are symmetric cranial nerve palsies accompanied by a symmetric descending weakness and flaccid paralysis without sensory deficits. Diagnosis is clinical and by laboratory identification of toxin. Treatment is with support and antitoxin.
C. botulinum elaborates 7 types of antigenically distinct neurotoxins (types A through G), which interfere with release of acetylcholine at peripheral nerve endings. Four of the toxins (types A, B, E, and rarely F) affect humans. Types A and B are highly poisonous proteins resistant to digestion by GI enzymes. About 50% of food-borne outbreaks in the US are caused by type A toxin, followed by types B and E. Type A toxin occurs predominantly west of the Mississippi River, type B in the eastern states, and type E in Alaska and the Great Lakes area (type E is frequently associated with ingestion of fish products). Type A toxin is used therapeutically to relieve excess muscle activity; botulinum toxin has also been developed as a bioweapon.
Botulism occurs in 3 forms:
In food-borne botulism, neurotoxin produced in contaminated food is eaten. Neurotoxin is elaborated in vivo by C. botulinum in infected tissue in wound botulism and in the large intestine in infant botulism (see Infant Botulism).
C. botulinum spores are highly heat-resistant and may survive boiling for several hours at 100° C. However, exposure to moist heat at 120° C for 30 min kills the spores. Toxins, on the other hand, are readily destroyed by heat, and cooking food at 80° C for 30 min safeguards against botulism. Toxin production (especially type E) can occur at temperatures as low as 3° C (ie, inside a refrigerator) and does not require strict anaerobic conditions.
Sources of infection:
Home-canned foods, particularly low-acid foods, are the most common sources, but commercially prepared foods have been implicated in about 10% of outbreaks. Vegetables, fish, fruits, and condiments are the most common vehicles, but beef, milk products, pork, poultry, and other foods have been involved. Of outbreaks caused by seafood, type E causes about 50%; types A and B cause the rest. In recent years, foods that are not canned (eg, foil-wrapped baked potatoes, chopped garlic in oil, patty melt sandwiches) have caused restaurant-associated outbreaks.
C. botulinum spores are common in the environment, and many cases may be caused by ingestion or inhalation of dust or by absorption through the eyes or a break in the skin.
Injecting drugs with unsterilized needles can cause wound botulism. Injecting contaminated heroin into a muscle or under the skin (skin popping) is riskiest.
Symptoms and Signs
Symptoms begin abruptly, usually 18 to 36 h after toxin ingestion, although the incubation period may vary from 4 h to 8 days. Nausea, vomiting, abdominal cramps, and diarrhea frequently precede neurologic symptoms. Neurologic symptoms are characteristically bilateral and symmetric, beginning with the cranial nerves and followed by descending weakness or paralysis. There are no sensory disturbances, and the sensorium usually remains clear.
Common initial symptoms and signs include dry mouth, blurred or double vision, drooping eyelids, slurred speech, and difficulty swallowing. Pupillary light reflex is diminished or totally lost. Dysphagia can lead to aspiration pneumonia. Muscles of respiration and of the extremities and trunk progressively weaken in a descending pattern. Fever is absent, and the pulse remains normal or slow unless intercurrent infection develops. Constipation is common after neurologic impairment appears. Major complications include respiratory failure caused by diaphragmatic paralysis and pulmonary infections.
Neurologic symptoms appear, as in food-borne botulism, but there are no GI symptoms or evidence implicating food as a cause. A history of a traumatic injury or a deep puncture wound (particularly if due to injection of illicit drugs) in the preceding 2 wk may suggest the diagnosis. A thorough search should be made for breaks in the skin and for skin abscesses caused by self-injection of illegal drugs.
Botulism may be confused with Guillain-Barré syndrome, poliomyelitis, stroke, myasthenia gravis, tick paralysis, and poisoning caused by curare or belladonna alkaloids. Electromyography shows characteristic augmented response to rapid repetitive stimulation in most cases.
In food-borne botulism, the pattern of neuromuscular disturbances and ingestion of a likely food source are important diagnostic clues. The simultaneous presentation of at least 2 patients who ate the same food simplifies diagnosis, which is confirmed by demonstrating C. botulinum toxin in serum or stool or by isolating the organism from stool. Finding C. botulinum toxin in suspect food identifies the source.
In wound botulism, finding toxin in serum or isolating C. botulinum organisms on anaerobic culture of the wound confirms the diagnosis.
Toxin assays are done only by certain laboratories, which may be located through local health authorities or the Centers for Disease Control and Prevention (CDC).
Anyone known or thought to have been exposed to contaminated food must be carefully observed. Administration of activated charcoal may be helpful. Patients with significant symptoms often have impaired airway reflexes, so if charcoal is used, it should be given via gastric tube, and the airway should be protected by a cuffed endotracheal tube.
The greatest threat to life is respiratory impairment and its complications. Patients should be hospitalized and closely monitored with serial measurements of vital capacity. Progressive paralysis prevents patients from showing signs of respiratory distress as their vital capacity decreases. Respiratory impairment requires management in an ICU, where intubation and mechanical ventilation are readily available. Improvements in such supportive care have reduced the mortality rate to < 10%.
Nasogastric intubation is the preferred method of alimentation because it simplifies management of calories and fluids, stimulates intestinal peristalsis (which eliminates C. botulinum from the gut), allows the use of breast milk in infants, and avoids the potential infectious and vascular complications inherent in IV alimentation.
Patients with wound botulism require wound debridement and parenteral antibiotics such as penicillin or metronidazole.
A new heptavalent equine antitoxin (A to G) is now also available in the US; it replaces the older trivalent antitoxin. Antitoxin does not inactivate toxin that is already bound at the neuromuscular junction; therefore, preexisting neurologic impairment cannot be reversed rapidly. (Ultimate recovery depends on regeneration of nerve endings, which may take weeks or months.) However, antitoxin may slow or halt further progression. In patients with wound botulism, antitoxin can reduce complications and mortality rate. Antitoxin should be given as soon as possible after clinical diagnosis and not delayed to await culture results. Antitoxin is less likely to be of benefit if given > 72 h after symptom onset.
One 20- or 50-mL vial of the heptavalent antitoxin, diluted 1:10, is given to adults as a slow infusion; dose and infusion rate are adjusted for infants and children. All patients who require the antitoxin must be reported to state health authorities, who then request the antitoxin from the CDC, which is the only source; practitioners cannot obtain antitoxin directly from the CDC. Because antitoxin is derived from horse serum, there is a risk of anaphylaxis or serum sickness. (For precautions, see Drug Hypersensitivity; for treatment, see Treatment.)
Because even minute amounts of C. botulinum toxin can cause serious illness, all materials suspected of containing toxin require special handling. Toxoids are available for active immunization of people working with C. botulinum or its toxins. Details regarding specimen collection and handling can be obtained from state health departments or the CDC.
Correct canning and adequate heating of home-canned food before serving are essential. Canned foods showing evidence of spoilage and swollen or leaking cans should be discarded.
Last full review/revision May 2013 by Joseph R. Lentino, MD, PhD
Content last modified July 2013