National case definition: Botulism

Date of last revision: November 2008

National notification

Only confirmed cases of disease should be notified.

Type of surveillance

Routine case-by-case notification to the federal level.

Case classification

Confirmed case

A confirmed case requires laboratory definitive evidence with clinical evidence or, in the case of foodborne botulism, clinical evidence and consumption of the same suspect food as an individual who has laboratory-confirmed botulism.

Foodborne botulism (Either 1 or 2)

  1. Laboratory confirmation of intoxication with clinical evidence:
    • detection of botulinum toxin in serum, stool, gastric aspirate or food
    • isolation of Clostridium botulinum from stool or gastric aspirate
  2. Clinical evidence and indication that the client ate the same suspect food as an individual with laboratory-confirmed botulism.

Wound botulism

Laboratory confirmation of infection:

  • laboratory detection of botulinum toxin in serum
  • isolation of C. botulinum from a wound
  • presence of a freshly infected wound in the 2 weeks before symptoms and no evidence of consumption of food contaminated with C. botulinum

Infant botulism

Laboratory confirmation with symptoms compatible with botulism in a person less than one year of age:

  • detection of botulinum toxin in stool or serum
  • isolation of C. botulinum from the patient’s stool or at autopsy

Colonization botulism

Laboratory confirmation with symptoms compatible with botulism in a patient aged 1 year or older with severely compromised gastrointestinal tract functioning (i.e. abnormal bowel) due to various diseases, such as colitis, or intestinal bypass procedures, or in association with other conditions that may create local or widespread disruption in the normal intestinal flora:

  • detection of botulinum toxin in stool or serum
  • isolation of C. botulinum from the patient’s stool or at autopsy

Probable case


A probable case requires clinical evidence and consumption of a suspect food item in the incubation period (12-48 hours).

Laboratory evidence

Laboratory confirmation (from CPHLN document)

Any of the following will constitute a case of botulism:

  • detection of botulinum toxin, with or without culture
  • isolation of C. botulinum

Approved/validated tests

  • Standard culture for C. botulinum with demonstration of neurotoxin.
  • C. botulinum neurotoxin mouse bioassay.

Indications and limitations

In wound and foodborne botulism C. botulinum neurotoxin may not be detectable in serum. Administration of antitoxin prior to withdrawal of blood will result in a negative assay.

While some strains of C. botulinum type C may not produce neurotoxin, two other species of the genus, C. baratii and C. butyricum may produce the neurotoxin.

Culture without toxin assay by mouse bioassay is not useful. Group I C. botulinum cannot be distinguished from C. sporogenes without toxin assay.

Isolates and/or clinical specimens should be referred to the National Botulism Reference Service or the British Columbia Centre for Disease Control

EIA for botulinum toxin is not as sensitive as the mouse bioassay and therefore should not replace the mouse bioassay for neurotoxin detection in clinical specimens; however, EIA could be used to detect neurotoxin production from cultures.

Clinical evidence

Foodborne: Clinical illness is characterized by blurred vision, dry mouth and difficulty swallowing and speaking. Descending and symmetric paralysis may progress rapidly, often requiring respiratory support.

Wound: Clinical illness is characterized by diplopia, blurred vision and bulbar weakness. Symmetric paralysis may progress rapidly.

Infant: Clinical illness in infants is characterized by constipation, loss of appetite, weakness, altered cry and loss of head control

ICD Code(s)

ICD-10 Code(s)

A05.1 Botulism (Classical foodborne intoxication due to Clostridium botulinum)

ICD-9/ICD-9CM Code(s)

005.1 Botulism

Type of international reporting

Under Article 6 of the International Health Regulations (IHR) (2005), each State Party shall notify the World Health Organization (WHO) by way of the IHR National Focal Point,Footnote 1 and within 24 hours of assessment of public health information, of all events which may constitute a public health emergency of international concern within its territory in accordance with the decision instrument (Annex 2 of the IHRFootnote 2), as well as any health measure implemented in response to those events.

  • Any event of potential international public health concern, including those of unknown causes or sources, shall lead to the utilization of the algorithm in Annex 2 of the IHR. The need to notify such events to the WHO will depend upon the outcome of the assessment using the Annex 2 decision instrument.

Note: If event does not meet the criteria for notification under Article 6 of the IHR, then other IHR-related reporting requirements may still apply with WHO and/or other States Parties, including those under Art. 7 (information-sharing during unexpected or unusual public health events), Art. 8 (consultation with WHO on public health events), Art. 9 (any public health risk that may cause international disease spread), Art. 10 (requests for verification from WHO), and Art. 44 (collaboration and assistance).


One case is considered an outbreak.

Probable case definitions are provided as guidelines to assist with case finding and public health management, and are not for national notification purposes.


CDC Notifiable Disease Case Definitions

Taillac PP, Kim J. CBRNE-Botulism. Last updated June 2006.

World Health Organization. International Health Regulations (2005). 3rd ed. Geneva, 2016.


Footnote 1

In Canada, the IHR National Focal Point is located at the Public Health Agency of Canada.

Return to footnote 1 referrer

Footnote 2

IHR Annex 2 Decision Instrument is on pages 43-46 of the IHR Third Edition (2005)

Return to footnote 2 referrer

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