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For further information, see CMDT Part 33-05: Clostridial Diseases

Key Features

Essentials of Diagnosis

  • Recent ingestion of home-canned or smoked foods; recovery of toxin in serum or food

  • Recent injection drug use

  • Diplopia, dry mouth, dysphagia, dysphonia

  • Muscle weakness progressing to respiratory paralysis

  • Normal sensory examination

  • Pupils are usually fixed and dilated

General Considerations

  • A paralytic disease caused by botulinum neurotoxin, which is produced by Clostridium botulinum, a ubiquitous, strictly anaerobic, spore-forming bacillus found in soil

  • Four toxin types—A, B, E, and F—cause human disease

  • Botulinum toxin inhibits release of acetylcholine at the neuromuscular junction

  • Naturally occurring botulism exists in three forms

    • Food-borne botulism

    • Infant botulism

    • Wound botulism

  • Food-borne botulism is caused by ingestion of preformed toxin present in canned, smoked, or vacuum-packed foods such as home-canned vegetables, smoked meats, and vacuum-packed fish

  • Infant botulism

    • Associated with ingestion of honey

    • Honey consumption is safe for children 1 year of age or older

  • Wound botulism

    • Often occurs in association with injection drug use

    • Results from organisms present in the gut or wound that secrete toxin

  • Botulinum toxin

    • Extremely potent

    • Classified by the CDC as a high-priority agent because of its potential for use as an agent of bioterrorism

Clinical Findings

Symptoms and Signs

  • Visual disturbances, particularly diplopia and loss of accommodation, appear 12–36 hours after ingestion of the toxin

  • Characteristic signs

    • Ptosis

    • Cranial nerve palsies with impairment of extraocular muscles

    • Fixed dilated pupils

  • Other symptoms

    • Dry mouth

    • Dysphagia

    • Dysphonia

  • Nausea and vomiting may be present, particularly with type E toxin

  • The sensory examination is normal

  • The sensorium remains clear and the temperature normal

  • Respiratory paralysis may lead to death unless mechanical assistance is provided

Differential Diagnosis

  • Because the clinical presentation of botulism is so distinctive and the differential diagnosis limited, botulism once considered is not easily confused with the other diseases listed below

    • Poliomyelitis

    • Guillain-Barré syndrome

    • Myasthenia gravis

    • Brainstem infarct or vertebrobasilar insufficiency

    • Basilar meningitis (infectious or carcinomatous)

    • Tick paralysis

    • Organophosphate poisoning

    • Intestinal obstruction/food poisoning (when nausea and vomiting are present)


  • Toxin in food and patients' serum may be shown by mouse inoculation and identified with specific antiserum



  • If botulism is suspected

    • Contact the CDC for advice and help with procurement of equine serum heptavalent botulism antitoxin and for assistance in obtaining assays for toxin in serum, stool, or food

    • Contact information for CDC case consultation is or 770-488-7100

    • Skin testing is recommended to exclude hypersensitivity to antitoxin preparation

    • Antitoxin should be given as early as possible, ideally within 24 hours of onset of symptoms, to arrest progression of disease

    • Do not delay administration of antitoxin to await laboratory confirmation ...

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