Two customers of a Chinese grocery in New York City likely fell ill with botulism after home-fermenting their tofu in January 2012, according to a new report by the U.S. Centers for Disease Control and Prevention. The illnesses happened 23 days apart, though investigators found that the patients — both Chinese immigrants — used similar fermentation practices in their homes. The patients purchased bulk tofu sold in unrefrigerated, uncovered, water-filled bins. Fermented tofu is a danger that public health professionals should be aware of, the CDC said. Following the illnesses, The New York City Department of Health and Mental Hygiene informed the grocery’s manager that the tofu needed to be stored below 41 degrees F and in closed containers. The first patient to visit the hospital was a 39 year-old man who had suffered four days of vomiting, followed by blurred vision, difficulty swallowing, speaking and breathing, and several nerve deficits including facial paralysis. He was admitted to the intensive care unit due to possible impending respiratory failure. He eventually tested positive for botulinum toxins. Admitted on March 3, 2012, the man remained in the hospital until March 26. Two days later, on March 28, the second patient, a 36 year-old woman, showed up to the same hospital. The second patient arrived after two days of vomiting and diarrhea, followed by difficulty speaking and breathing, as well as dizziness. Doctors immediately suspected botulism because of the symptoms and the previous patient’s history, but they could not detect botulinum toxin in any lab samples. Patient #2 was released on April 18. Patient #1 had shared home-fermented tofu with his wife, who did not exhibit any symptoms of poisoning. Investigators isolated botulinum from Patient #1’s tofu, but could not find it on the sample taken from Patient #2, nor from samples taken from the grocery store in March. The investigation was made difficult by the fact that tofu is not often associated with botulism poisoning in the U.S., the CDC noted, and only one other such outbreak has been recorded. But home-fermented tofu and other fermented bean products are the leading cause of botulism poisoning in China. Clostridium botulinum spores grow in air-tight environments on foods with low-acid, low-salt, and low-sugar content. The spores can grow unevenly in food, which might explain why Patient #1’s wife was not sickened and why investigators couldn’t find evidence of contamination in Patient #2’s leftovers.