Botulism From Home-Canned Cactus (Nopales) at Family Gatherings in Fresno, 2024

Foodborne botulism is a rare, potentially fatal illness caused by eating food that contains botulinum neurotoxin, made by the bacterium Clostridium botulinum or, rarely, related Clostridium species. The bacteria can grow in food that is improperly prepared or stored, such as home-canned or home-preserved vegetables. This outbreak in Fresno County, California, was the first reported to be linked to home-canned nopales, the prickly pear cactus pads popular in traditional Mexican cooking.

How it unfolded

• June 21 and 22, 2024: two related family gatherings, held indoors while outdoor temperatures topped 100°F (37.8°C). Leftovers from the first were served again at the second. In all, 31 people attended one or both.
• June 23: a 42-year-old woman, patient A, went to a Fresno County hospital with 12 hours of dizziness, sore throat and stomach symptoms. She was diagnosed with heat-related dehydration and sent home. She came back the next morning but left without being seen.
• June 25: she returned with persistent dizziness, blurred vision, a drooping eyelid and trouble swallowing, and within six hours of arrival was on a ventilator for impending respiratory failure. Her progressive, descending paralysis, a hallmark of botulism, raised suspicion. The same day, six other relatives who had been at the gatherings came to that hospital or a second one with neurologic symptoms that began June 23 or 24. The hospital alerted the California Poison Control System and the Fresno County Department of Public Health, which began an investigation and, through the California Department of Public Health, requested antitoxin from CDC.
• June 27: three more attendees were hospitalized with neurologic complaints.

The patients

Ten attendees were hospitalized, five at each hospital. Eight were diagnosed with botulism; the other two were found, after examination and observation, to have anxiety symptoms. The eight patients were all Hispanic or Latino, five were women, and their median age was 44 (range 24–59). The most common findings were double vision (eight patients), hoarseness (seven), dizziness (six) and trouble swallowing (six). Six were admitted to intensive care and two, patients A and B, needed a ventilator. Hospital stays ranged from 2 to 42 days (median 4). All eight received antitoxin, survived, and recovered fully.

The source

The eight people with botulism were the only attendees who ate the nopales salad; patient A, the sickest, ate it at both gatherings. Other food included pork tamales and hamburgers.

The woman who made the salad (patient D) used fresh onions and tomatoes with nopales she had preserved herself. She had sterilized empty glass jars by dipping them in boiling water, filled them with chopped raw nopales and a little salt, sealed them with new metal lids, and kept them for six weeks in an outdoor shed. She had preserved food this way for years, as friends and relatives had taught her, and did not know it carried a risk of botulism.

Inspectors collected leftovers from patient A's home, including the discarded nopales salad, and 23 jars of nopales or tomatoes from patient D's unair-conditioned shed; the jars were reused commercial containers, some with badly corroded lids. At the state laboratory, serum from five of the eight patients tested positive for botulinum toxin type A. Two stool samples were negative, as were the one jar of nopales and one jar of tomatoes tested, but type A toxin was found in the discarded nopales salad, confirming the source.

Getting antitoxin fast

The antitoxin, equine heptavalent botulinum antitoxin (HBAT), is the main treatment for botulism in anyone older than an infant, but hospitals do not stock it; CDC keeps it at port health stations at major airports. State health officials called CDC within two hours of the first hospital's call and asked for eight doses. Helicopters carried the antitoxin from two CDC stations to Fresno's regional airport, and the California Highway Patrol took it on to both hospitals. Six patients received it on the evening of June 25, about eight hours after the request. The two unused doses were kept at the first hospital and given within four hours to the two patients who arrived on June 27. The outbreak briefly emptied California's CDC stockpile, which was restocked within 48 hours.

Lessons

Botulism causes paralysis that descends from the head, starting with the cranial nerves, then weakening the arms and legs, and finally the muscles used for breathing. Early signs such as dizziness, blurred vision and trouble swallowing are easy to miss, and delays can hold up treatment. Clinicians who suspect botulism should immediately notify their local or state health department, which can arrange CDC consultation and antitoxin, and should give antitoxin without waiting for lab confirmation when suspicion is high, since it stops the disease from progressing by binding the toxin in the blood.

Improperly processed, fermented, preserved, stored or refrigerated food can let the bacteria grow and make toxin, especially low-acid food kept warm and sealed from air. Home-canned and fermented vegetables are the most common cause of foodborne botulism in the continental United States. Low-acid foods like nopales must be processed in a pressure canner, with jars sterilized both empty and after filling, not just by dipping empty jars in boiling water. The authors call for home preservation and canning guidance in accessible language and culturally sensitive forms, so communities can prevent future outbreaks.

Sources

• Vohra R, Barash JR, Karmarkar EN, et al. Foodborne Botulism Outbreak After Consumption of Home-Canned Cactus (Nopales) — Fresno County, California, June 2024. MMWR Morb Mortal Wkly Rep 74(24). https://www.cdc.gov/mmwr/volumes/74/wr/mm7424a1.htm
• The report was led by the Fresno County Department of Public Health with the California Department of Public Health, the California Poison Control System, local hospitals and CDC; its figures are not reproduced here.