NORD gratefully acknowledges Kevin Chatham-Stephens, MD, Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention, for assistance in the preparation of this report.
Botulism is a rare but serious paralytic illness caused by a toxin usually produced by the bacterium Clostridium botulinum. There are four generally recognized naturally-occurring types; foodborne, wound, infant, and, rarely, adult intestinal colonization. Iatrogenic and inhalational botulism may also occur. Foodborne botulism is caused by eating foods that contain botulinum toxin. Wound botulism occurs when C. botulinum spores germinate and produce toxin in a contaminated wound or abscess. The most common form of botulism in the United States, infant botulism, is caused when ingested C. botulinum spores colonize and subsequently produce toxin in the intestines of affected infants. In rare instances, C. botulinum intestinal colonization and toxin production have also occurred among adults with anatomical or functional bowel abnormalities. Additionally, iatrogenic botulism has infrequently occurred after intramuscular injection of botulinum toxin for treatment of certain dystonias and other disorders. Finally, inhalational botulism, though not naturally-occurring, was reported among three German laboratory workers who inadvertently inhaled aerosolized toxin, and could potentially occur after a deliberate aerosolization of toxin in a bioterrorism event. Any case of foodborne or unexplained botulism is considered to be a public health emergency because of the potential for toxin-containing foods to injure others who eat them and because of the potential misuse of botulinum toxin as a biological weapon. State and local public health officials by law must be informed immediately whenever botulism is suspected in a human patient.
The incubation period for foodborne botulism is usually 12 – 36 hours but may range from a few hours to 10 days. Symptom onset might occur faster in an inhalational botulism scenario. Symptoms can range from mild to severe. The classic medical triad of botulism is a weakness or paralysis and reduced muscle tone in a patient without fever (afebrile) and with a clear sensorium (alert and able to respond to questions). Fever might occur after a secondary infection (e.g., aspiration pneumonia).
The progression of illness is similar among patients with different types of botulism (foodborne, wound, inhalational) except that foodborne botulism patients often experience gastrointestinal symptoms such as nausea, vomiting, and diarrhea that precede the onset of neurologic illness.
The typical neurologic presentation of botulism is a symmetric (same on both sides of the body), descending flaccid paralysis that begins in the nerves that control the muscles in the face, head, and neck (cranial nerves) and progresses to include proximal muscle groups such as hip and shoulder muscles and then distal extremity muscle groups such as muscles of wrists, hands, and feet. Severe illness can result in respiratory paralysis and death. Some patients also experience abdominal pain or cramping, constipation or ileus (paralytic obstruction of the intestines), and urinary retention. Sensory deficits or paresthesias are uncommon but can occur, and mental status typically remains clear provided the patient is adequately oxygenated.
Cranial nerve deficits are usually bilateral and typically precede respiratory impairment or extremity weakness. Eye signs or symptoms may include double vision (diplopia) and/or blurred vision, impaired functioning of the muscles of the eyes (ophthalmoplegia), droopy eyelids (ptosis), dilation of the pupil (mydriasis), and depressed or loss of pupillary constriction to light. Other findings may include difficulty speaking (dysphonia) or slurred speech (dysarthria), difficulty in swallowing (dysphagia), a dry mouth and very dry or sore throat. Some individuals have a tongue that appears swollen or “coated” due to its dryness. The gag reflex may be suppressed.
Affected individuals may experience generalized muscle weakness, often progressing rapidly from the head to involve the neck, arms, chest, and legs. The weakness is usually the same on both sides of the body (symmetric), descending, and spreads from proximal to distal muscle groups. Weakening of the deep tendon reflexes (hyporeflexia) or complete loss of reflexes (areflexia) may also be present. Difficulty breathing may also be present, and may progress to respiratory failure from pharyngeal and upper airway muscle paralysis as well as paralysis of the diaphragm and accessory muscles of respiration.
Wound botulism is characterized by the same neurological symptoms as foodborne botulism. However, the affected individual typically experiences no gastrointestinal symptoms and no food can be implicated as the cause. The skin must be carefully checked for wounds. In the United States, wound botulism most commonly occurs among users of injection drugs, particularly black tar heroin. Wound botulism may rarely occur after traumatic injury involving contamination with soil, or potentially after surgery. A fever due to infection from other bacteria may be present.
Infant botulism generally affects infants under 12 months of age. The action of the toxin in the body produces constipation, weakness (notably of gag, cry, suck, and swallow), loss of muscle tone, and ultimately, limp (flaccid) paralysis. The severity and rapidity of onset of the disease varies greatly among affected infants. In the absence of complications, recovery is complete.
Foodborne botulism is the result of ingestion and absorption of toxin that is produced by C. botulinum in contaminated foods. Wound botulism is caused by toxin produced from a wound infected with C. botulinum. Unlike foodborne and wound botulism, infant botulism and adult intestinal colonization botulism result from ingestion of the bacterial spore(s) that grow and produce botulinum toxin within the large intestine. Honey is the one identified and avoidable food reservoir of these spores for infant botulism. After testing over the years of hundreds of foods, beverages and other items placed in infants’ mouths with negative results, it was concluded that the source of spores for most infant botulism patients is unknown but may be from ingestion of microscopic dust particles on which the spores travel.
Botulinum toxin causes weakness and loss of muscle tone because it blocks the nerve ending’s ability to signal the linked muscle to contract.
The bacterium C. botulinum is found in soils and marine sediments throughout the world. In the United States, foodborne botulism has been associated primarily with home-canned foods, particularly vegetables, and with Alaska Native foods, especially fermented fish.
C. botulinum typically produces one of seven distinguishable toxin types, arbitrarily designated by the letters A through G. Botulism in humans is usually caused by toxin types A, B, and E, and rarely F. Most foodborne botulism is caused by contaminated home-canned foods, though outbreaks also occur from commercial foods, restaurant foods, or improper food handling practices. Foodborne botulism may also be associated with the ingestion of baked potatoes that have been stored (for extended periods of time) in aluminum foil at room temperature and with certain condiments, such as onion or garlic, stored in oil. Drinking alcohol made illicitly in prisons, known as hooch or pruno, has also been associated with botulism outbreaks. Outbreaks of type E are usually associated with consumption of preserved, uncooked foods prepared from aquatic (freshwater or marine) fish or mammals. Types A and B are the principal causes of infant and wound botulism.
Infant botulism occurs globally and is the most common form of human botulism in the United States. Patients diagnosed with botulism demonstrated a predominance of toxin type A west of the Rocky Mountains and type B east of the Rocky Mountains, while type E is more prevalent in the Pacific Northwest, Alaska and the Great Lakes area. Type E also occurs in northern latitudes and Japan. National botulism surveillance information is available from Centers for Disease Control and Prevention (CDC) at the following link:
The clinical diagnosis of botulism may be made based upon a thorough clinical evaluation and a detailed patient history. The mouse bioassay is the “gold standard” method for laboratory confirmation of the clinical diagnosis and may demonstrate the presence of botulinum toxin in serum, gastric fluid, stool, or food (foodborne botulism) specimens. Botulism can also be confirmed by culture of C. botulinum organisms from gastric fluid, stool, or a contaminated wound (wound botulism).
It is essential that both home-canned and commercially-canned foods be prepared and stored properly to prevent the production of botulinum toxin. Food that shows any sign of spoilage should be discarded.
The following link provides information about proper techniques for canning:
Clostridium botulinum spores are highly resistant to heat and may survive for several hours at temperatures of 100 C. Exposure to heat at 120 C destroys C. botulinum spores. In contrast to spores, botulinum toxin is easily inactivated by heat; thus, thoroughly heating food at 85 C or boiling may inactivate toxin. While home-canned food is the most common source for botulism, commercially prepared foods have been implicated as well. Vegetables, fish, and condiments are the most commonly implicated foods; however, beef, dairy products, pork, poultry, and other foods have also been implicated. To reduce the risk of infant botulism, honey should not be fed to infants less than 12 months of age.
Since respiratory impairment and its complications may be life-threatening, affected individuals should be hospitalized, closely supervised and promptly treated with antitoxin. Botulism is a public health emergency because of the severity of illness and because a single case may be the harbinger of many more. Physicians in the United States who suspect botulism should immediately consult with their local or state health department, no matter how low the suspicion. Health departments may then contact Centers for Disease Control and Prevention (CDC) to discuss appropriate testing and treatment of suspected patients. Rapid notification of public health personnel ensures timely treatment if indicated. It also enables rapid identification or prevention of related cases of botulism. State health departments and CDC are available 24 hours a day, 7 days a week through emergency contact numbers to respond to suspect botulism cases. If physicians are unable to reach their health department, they may contact CDC’s Emergency Operations Center at (770) 488-7100.
CDC provides additional information about botulism online at:
Mechanical ventilation in cases of respiratory failure, and supportive care are known to save lives. Intravenous equine antitoxin, administered early in the course of illness, is the only specific treatment available for botulism. Antitoxin will not reverse established neurological deficits; improvement of impairment requires nerve regeneration and takes time. Antitoxin may, however, prevent the progression of disease. Heptavalent botulinum antitoxin that covers all 7 known botulinum toxin types and is relatively despeciated is available from CDC. Treatment should be initiated soon after botulism is suspected. However, the risks of treatment must be weighed against potential benefits.
For the treatment of infant botulism, physicians may obtain Botulism Immune Globulin Intravenous (Human) (BabyBIG®) from the California Department of Public Health, Infant Botulism Treatment and Prevention Program (IBTPP) following clinical consultation with the on-call Program physician. BabyBIG® has been shown in clinical studies to substantially reduce the length and cost of hospital stay for infants treated within seven days of hospital admission. For suspected cases of infant botulism, the attending physician should first contact their state health department, and then may contact IBTPP at (510) 231-7600 (24 hours, 7 days) to request BabyBIG®. The IBTPP webpage at www.infantbotulism.org has additional information.
Antibiotics are not typically used to treat botulism. If antibiotics are needed to treat an infection in a botulism patient (e.g., wound infection, pneumonia), then certain types of antibiotics (e.g., aminoglycosides) should be avoided, if possible, because they can worsen the muscle weakness.
Historically, guanidine was used to treat some patients affected with botulism, but it is no longer used.
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