Risk factors for botulism are best understood by transmission category, because the exposure that permits toxin production differs by form. For infant and adult intestinal colonization botulism, the risk is ingestion of C. botulinum spores that then colonize a susceptible gut. For foodborne botulism, the risk is ingestion of preformed toxin from improperly preserved food. For wound botulism, the risk is contamination of devitalized tissue, now overwhelmingly from injection drug use. Iatrogenic botulism is an emerging category driven by cosmetic/therapeutic botulinum toxin injection.^[1][2]

Infant botulism results from ingested spores that germinate in the immature large intestine, where the developing microbiota does not yet suppress colonization. Recognized risk factors include:^[3][4]

• Age younger than 12 months (susceptible gut flora), with ~88% of cases occurring at ≤6 months of age.^[5]
• Environmental spore exposure — the leading presumed source in the United States: airborne/household dust, nearby soil disturbance, construction, and rural or agricultural living.
• Honey ingestion — the only definitively established, avoidable food source, but responsible for a minority of U.S. cases (~4%); honey exposure is higher among European and Middle Eastern cases.
• Rarely implicated foods — powdered (nonsterile) infant formula, infant rice cereal, well water, and herbal teas (e.g., chamomile) have each been linked in isolated reports.

Corn syrup has never been proven to cause infant botulism, and lack of honey exposure does not exclude the diagnosis.^[6][7]

Foodborne botulism follows ingestion of preformed toxin from food in which spores germinated under anaerobic, low-acid (pH >4.6), low-salt, low-sugar conditions. Risk factors relate to food handling rather than the host:^[8][9]

• Improper home canning/preservation of low-acid foods (the most common U.S. cause) — home-canned vegetables (asparagus, green beans, beets, corn), and, in ethnic cuisines, home-preserved items such as prickly-pear cactus (nopales) and bamboo shoots.
• Inadequate refrigeration of cooked foods, including foil-wrapped baked potatoes and oil infusions (e.g., garlic-in-oil).
• Fermented aquatic foods — fermented fish/marine mammal products (Alaska Native cuisine; type E).
• Uncommon vehicles — commercially processed foods, restaurant-held foods, and prison-made illicit alcohol (“pruno”).

Wound botulism requires contamination of devitalized tissue with spores that germinate anaerobically. Risk factors:^[10][11]

• Injection drug use — the dominant modern risk factor, especially black tar heroin and subcutaneous/intramuscular injection (“skin popping”), with a dose-response relationship to the amount injected; rarely methamphetamine. Compared with injectors who never skin-popped, occasional skin-poppers had ~6-fold and heavy users ~25-fold higher adjusted odds of wound botulism.^[12]
• Chronic intranasal cocaine use with sinus/nasal lesions (rare).
• Gross traumatic or crush injury with devitalized/contaminated tissue (historically predominant; now less common), including open fractures.

This rare form is the adult/older-child analogue of infant botulism, in which ingested spores colonize an abnormal gut. Predisposing risk factors:^[13][14]

• Prior bowel or gastric surgery, short-bowel syndrome, or anatomical bowel abnormalities.
• Inflammatory bowel disease / Crohn disease and small-intestinal bacterial overgrowth.
• Recent antimicrobial therapy (disrupts protective flora).

Iatrogenic botulism follows systemic spread of injected botulinum toxin. Risk factors identified in recent case series:^[15][16][17]

• Unlicensed, counterfeit, or unknown-brand products.
• Injection in non-authorized institutions / by untrained injectors.
• Excessive or off-label high-dose administration (higher dose is associated with shorter latency to symptoms).

• Advise against feeding honey to infants <12 months, but do not exclude infant botulism when honey exposure is absent—most U.S. cases are environmental.^[18]
• Screen for injection drug use (skin popping, black tar heroin) in any adult with descending paralysis, even without an obvious wound; consider botulism when weakness fails to respond to naloxone.^[19]
• Ask about recent cosmetic/therapeutic botulinum toxin injection, especially unlicensed products, in new-onset bulbar/descending weakness.^[20]
• Suspect adult intestinal colonization in the classic syndrome with no food/wound source and a predisposing gut condition.^[21]

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