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Botulism

By Joseph R. Lentino, MD, PhD, Loyola University Stritch School of Medicine;Hines VA Hospital

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Botulism is poisoning that is due to Clostridium botulinum toxin and that affects the peripheral nerves. Botulism may occur without infection if toxin is ingested, injected, or inhaled. 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 is one of several species of clostridia that cause human disease. Botulism is a rare, life-threatening disorder that occurs when botulinum toxin spreads hematogenously and interferes with release of acetylcholine at peripheral nerve endings. Botulism is a medical emergency and sometimes a public health emergency.

C. botulinum elaborates 8 types of antigenically distinct neurotoxins (types A through H). Five of the toxins (types A, B, E, and rarely F and H) 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 H is the most potent toxin known.

Botulism can occur when neurotoxin is elaborated in vivo by C. botulinum or when it is acquired.

In vivo elaboration causes the following forms:

  • Wound botulism

  • Infant botulism (the most common form)

  • Adult enteric botulism (rare)

In wound botulism, neurotoxin is elaborated in infected tissue.

In infant botulism and in adult enteric botulism, spores are ingested, and neurotoxin is elaborated in the GI tract. Adult enteric botulism usually occurs only in adults with impaired resistance.

Acquisition of preformed neurotoxin causes the following forms:

  • Food-borne botulism

  • Iatrogenic botulism

  • Inhalation botulism

In food-borne botulism, neurotoxin produced in contaminated food is eaten.

In iatrogenic botulism, type A toxin is injected therapeutically to relieve excess muscle activity; rarely, botulism has occurred after cosmetic injections.

In inhalation botulism, toxins becomes aerosolized either accidentally or when intentionally used as a bioweapon; aerosolized toxins do not occur in nature.

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.

Pearls & Pitfalls

  • C. botulinum can produce toxin at temperatures as low as 3° C, so if food is contaminated, refrigeration is not protective.

Sources of toxin

Home-canned foods, particularly low-acid foods (ie, pH > 4.5), are the most common sources of ingested toxin, but commercially prepared foods have been implicated in about 10% of outbreaks. Vegetables (but usually not tomatoes), 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.

Sometimes the toxin is absorbed through the eyes or a break in the skin and, in such cases, may cause serious disease.

C. botulinum spores are common in the environment; most cases of infant botulism are caused by ingestion of spores.

Spores can also enter the body when drugs are injected with unsterilized needles; wound botulism may result. Injecting contaminated heroin into a muscle or under the skin (skin popping) is riskiest; it can cause gas gangrene.

If botulinum toxins enter the bloodstream, botulism results, regardless of how the toxins are acquired.

Symptoms and Signs

Common botulism symptoms and signs include

  • Dry mouth

  • Blurred or double vision

  • Drooping eyelids

  • Slurred speech

  • Dysphagia

Pupillary light reflex is diminished or totally lost. Dysphagia can lead to aspiration pneumonia. These 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.

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

  • Pulmonary and other nosocomial infections

Food-borne botulism

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.

Wound botulism

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.

Diagnosis

  • Toxin assays

  • Sometimes electromyography

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).

Treatment

  • Supportive care

  • Equine heptavalent antitoxin

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

  • 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.

Antitoxin

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 Anaphylaxis : Treatment.)

Prevention

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.

Key Points

  • Botulism may develop from ingestion of food-borne toxin, from elaboration of toxin from a clostridial wound infection, or, in infants, from ingestion and enteric colonization by C. botulinum spores.

  • Botulism may result from man-made botulism toxin that is injected therapeutically or for cosmetic reasons or is inhaled (in an aerosolized form).

  • Botulinum toxins block release of acetylcholine at peripheral nerve endings and cause bilateral, symmetric, descending weakness, beginning with the cranial nerves.

  • Sensation and mental status are unaffected.

  • Cooking destroys botulinum toxin but not the spores.

  • For diagnosis, use toxin assays.

  • Give equine antitoxin obtained from CDC via the state department of health.

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* This is the Professional Version. *