The New York City Department of Health and Mental Hygiene is investigating one confirmed and one suspect case of botulism and has issued a warning about unrefrigerated fresh bulk tofu, which is the possible but unconfirmed source of the illnesses.

New York City has seen only one other case of foodborne botulism in the past 15 years.

In this case, both patients are Chinese-speaking Queens residents who had recently purchased unrefrigerated fresh bulk tofu from the same store in Flushing, the health department said in a news release. The tofu was not made at this store, and its source is still under investigation.

As the investigation continues, the Health Department is advising that all fresh bulk tofu purchased from any New York City store should be discarded if it was kept at room temperature at the time of purchase.

The Health Department is also warning consumers to throw away any tofu at home that has not been stored in a refrigerator.

The tofu in question can be fermented and also made into a popular Chinese dish known as stinky tofu (chou doufu). Anyone who has made fermented tofu from fresh bulk tofu should also throw it away, the health department said in its warning notice.

Cooking this type of tofu is not a safeguard against botulism; the organism’s spores can still remain in the tofu and, if the tofu is improperly handled, the spores can produce the Clostridium botulinum toxin that causes illness.

Pre-packaged tofu products which are refrigerated are safe.

The symptoms of botulism include blurred or double vision, weakness or paralysis, poor reflexes, difficulty swallowing and speaking, and difficulty breathing. Symptoms of foodborne botulism usually occur 12-36 hours after ingestion, but may take several days. If left untreated, botulism can be fatal.

Although botulism can be diagnosed based on clinical symptoms, its differentiation from other diseases is often difficult — especially in the absence of other known persons affected by the condition. Once suspected, the most direct and effective way to confirm the diagnosis of botulism in the laboratory is testing for the presence of the botulinum toxin in the serum, stool, or gastric secretions of the patient.

The food consumed by the patient can also be tested for the presence of toxins. Currently, the most sensitive and widely used method for the detection of the toxins is the mouse neutralization test, which involves injecting serum into mice and looking for signs of botulism. This test typically takes 48 hours, while the direct culturing of specimens takes 5-7 days. Some cases of botulism may go undiagnosed because symptoms are transient or mild, or are misdiagnosed as Guillain-Barre Syndrome. 

If diagnosed early, foodborne botulism can be treated with an antitoxin that blocks the action of toxin circulating in the blood. This can prevent patients from worsening, but recovery still takes many weeks. The mainstay of therapy is supportive treatment in intensive care, and mechanical ventilation in case of respiratory failure, which is common.