What laboratory tests are recommended for a 5-week-old infant suspected of having botulism?

Laboratory Testing for Suspected Infant Botulism in a 5-Week-Old

For a 5-week-old infant with suspected botulism, immediately collect stool specimens (rectal swabs are acceptable in infants) and serum for botulinum toxin detection and Clostridium botulinum isolation—these are the only laboratory tests needed for diagnosis, and treatment decisions must be made clinically without waiting for results. 1

Essential Specimens to Collect

Stool Specimen (Highest Yield)

• Collect stool as the primary diagnostic specimen for both toxin detection and organism isolation 1
• Optimal amount is 10-20 g, but smaller amounts are acceptable in infants 1
• Rectal swabs are specifically acceptable for infants and young children when stool cannot be obtained 1
• Stool can detect both botulinum toxin AND Clostridium botulinum organisms 1
• If constipated (common in infant botulism), perform enema with sterile nonbacteriostatic water—never use tap water or glycerin-containing suppositories as these interfere with testing 1

Serum Specimen

• Collect 4 mL of serum minimum (smaller volumes acceptable for infants, though 4 mL is the minimum for mouse bioassay) 1
• Blood must be collected WITHOUT anticoagulant 1
• Tests only for botulinum toxin, not organisms 1
• Collect before antitoxin treatment if possible, though do not delay antitoxin administration to obtain specimens 1

Critical Timing Considerations

Collect specimens immediately upon suspicion—botulinum toxin irreversibly binds within neurons and drops below detectable levels in serum, stool, and gastric fluid over time 1. The longer you wait, the more likely laboratory confirmation will fail despite true disease 1.

Laboratory confirmation takes 24-48 hours for preliminary toxin results and up to 96 hours for final results, with organism identification taking 2-3 weeks 1. Treatment decisions cannot wait for these results 1.

What NOT to Order

• No routine blood work (CBC, CMP, inflammatory markers) is indicated specifically for botulism diagnosis—these are nonspecific and do not aid in diagnosis 1
• No imaging studies are diagnostic for botulism 1
• No gastric aspirate unless foodborne botulism is suspected (not applicable to infant botulism) 1
• No wound cultures (only relevant for wound botulism) 1

Laboratory Confirmation Criteria

Infant botulism is confirmed by detecting: 1

• Botulinum toxin in stool or serum, OR
• Isolation of Clostridium botulinum from stool

The mouse bioassay is the FDA-approved gold standard, though it may miss low toxin levels sufficient to cause human illness 1. In 5 cases from one series, stool culture was positive but mouse bioassay was negative or nonspecific, suggesting culture may be more sensitive in some instances 2.

Specimen Handling

• Refrigerate immediately at 36°F-46°F (2°C-8°C) 1
• Never freeze specimens 1
• Transport with cold packs 1
• Contact state/local public health department immediately for coordination of testing and antitoxin 1

Common Pitfalls

• Waiting for laboratory confirmation before treating—this is the most critical error, as antitoxin efficacy decreases with delayed administration 1
• Using tap water for enemas—this interferes with laboratory testing 1
• Collecting blood with anticoagulant—this invalidates serum testing 1
• Ordering unnecessary tests that delay recognition and treatment 1
• Failing to notify public health authorities immediately 1

Additional Context

In a substantial proportion of cases, laboratory results are negative despite clinical certainty of botulism, typically because specimens were collected late in illness when toxin levels fell below detection limits 1. Negative laboratory results do not exclude botulism 1. The diagnosis remains primarily clinical, with laboratory testing serving to confirm the diagnosis, identify the toxin serotype, and support public health investigation 1.