Botulism Workup

Updated: Dec 07, 2022
  • Author: William N Bennett, V, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Approach Considerations

High clinical suspcicion and clinical diagnosis with immediate antitoxin administration is the cornerstone of management, as laboratory tests are not helpful in the routine diagnosis of botulism. [6]  

A clinical criteria tool for early diagnosis has been developed for outbreak settings. [27]  

When botulism is suspected, consult public health officials immediately, request antitoxin, and if transferring to a higher level of care consider administering antitoxin before transfer. [28]  Full neurologic exam, brain imaging, lumbar puncture, electromyography, nerve conduction studies, and monitoring for anaphylaxis after antitoxin administration should be performed as applicable.

WBC counts and erythrocyte sedimentation rates are usually normal. [29]  Cerebrospinal fluid is also normal, except for occasional mild elevations in protein concentration.


Laboratory Studies

Laboratory confirmation of botulism requires either botulinum neurotoxin isolation or growth of a botulinum neurotoxin-producing ​Clostridium species (ie, C botulinum, C baratii, or C butyricum) in a stool, gastric aspirate, food, or wound culture. 

Botulinum neurotoxin isolation requires intraperitoneal injection of the patient' serum, fluid extract of food or feces, etc. into pairs of mice with and without monovalent antitoxin followed by observation for development of clinical botulism. [6, 30]  This test was standardized in the 1970s and has limited sensitivity depending on the mode of toxin exposure. These assays are limited to specific state public health and CDC laboratories, where other assays may also be used to determine neurotoxin serotype. Patient samples must be collected prior to administration of antitoxin, but antitoxin administration must not be delayed in order to obtain samples (serum 5-15 mL, stool 10-20 g, gastric aspirate 5-10 mL, suspected food source 10-20 g or mL). [1]   

To send a specimen to the CDC for testing [1] :

  • Call CDC consultant to discuss submission of specimens through local or state health department or state public health laboratory
  • Maintain the specimen at 36 oF-46 oF and ship with cold packs
  • Label package as required for Category B substances
  • Include completed CDC 50.34 with selected test order CDC-10132, Botulism Laboratory Confirmation and include phone and fax numbers for the state health department and hospital
  • Send package to: STAT (Attn: Botulism Lab, Unit 26) Centers for Disease Control and Prevention1600 Clifton Rd NE, Atlanta, GA 30329
  • Provde a tracking number to the CDC National Botulism Laboratory 

C botulinum may be grown on selective media from samples of stool or foods. Note that the specimens for toxin analysis should be refrigerated (not frozen), but culture samples of C botulinum should not be refrigerated.  Final results from culture for Clostridium species may take 2-3 weeks.

Because intestinal carriage is rare (and adult intestines typically do not allow for germination), identifying the organism or its toxin in vomitus, gastric fluid, or stool strongly suggests the diagnosis. [4]  Isolation of the organism from food without toxin is insufficient grounds for the diagnosis. Only experienced personnel who have been immunized with botulinum toxoid should handle the specimens. Because the toxin may enter the blood stream through the eye or via small breaks in the skin, precaution is warranted.

Wound cultures that grow C botulinum suggest of wound botulism.


Imaging Studies

Imaging studies are generally not useful in the diagnosis of botuli. [31]

The only potential role for imaging studies (eg, CT scan, MRI) would be to rule out CNS pathology, such as intracranial mass lesions, cerebrovascular disease of the brainstem, or basilar artery stroke, in patients in whom the presentation is atypical or vague.


Other Tests

Results from nerve conduction studies are normal, and electromyography (EMG) reveals reduced amplitude of compound muscle action potentials. [7, 8]

EMG may be useful in establishing a diagnosis of botulism, but the findings can be nonspecific and nondiagnostic, even in severe cases. Characteristic findings in patients with botulism include brief low-voltage compound motor-units, small M-wave amplitudes, and overly abundant action potentials. An incremental increase in M-wave amplitude with rapid repetitive nerve stimulation may help to localize the disorder to the neuromuscular junction. Single-fiber EMG may be a more useful and sensitive method for the rapid diagnosis of botulism intoxication, particularly in the absence of signs of general muscular weakness.

The results of the edrophonium chloride, or Tensilon, test for myasthenia gravis may be falsely positive in patients with botulism. [32]  If positive, it is typically much less dramatically positive than in patients with myasthenia gravis.