Health officials are warning Americans after 31 US states have been affected by the food- and waterborne illness, which is known to cause “explosive” diarrhea, the Centers for Disease Control and Prevention said in an update on Friday, July 10.

The gastrointestinal disease is caused by a microscopic parasite called Cyclospora, and researchers are still working to determine the source of the outbreak. 

“Since May 1, 2026, CDC has received reports of 843 confirmed domestic cases of cyclosporiasis and is aware of more than 1,500 cases that require further analysis to confirm the illness as domestically acquired cyclosporiasis,” the agency said. “So far this year, multiple states have reported an increase in cases in the last two weeks compared to the same period in 2025.”

No deaths have been reported as of Friday, though nearly 90 people have been hospitalized. 

The cyclosporiasis season is generally from May 1 through August 31, per the CDC. The higher-than-normal temperatures could be a factor in the rise in cases. 

“It’s warm weather,” Dr. Kavita Patel, a medical contributor for NBC News, told the outlet in an on-camera interview. “And that’s definitely a source of Cyclospora, which is causing this illness.”

Dr. Patel added that the single-cell parasite “just loves this type of weather.”

Additionally, she said the high number of cases could also be attributed to doctors actually “looking for it” amid reports of an outbreak.

Cyclospora symptoms — which typically begin approximately a week after exposure — include stomach issues such as severe abdominal cramps, bloating, increased gas, and nausea. Loss of appetite, significant weight loss, extreme fatigue, and muscle aches can also be signs.

Some who become ill also experience vomiting and a low-grade fever in addition to frequent, sometimes explosive, watery diarrhea.

The parasite can be spread through contaminated produce that has not been properly cleaned. Dr. Patel added that water contaminated with feces can also cause the illness.

American cases of cyclosporiasis have previously been linked to fresh produce like basil, cilantro, mesclun lettuce, raspberries, and snow peas, per the CDC. It is recommended to carefully wash the products.

“To date, no outbreaks have been linked to commercially frozen or canned produce,” the CDC said in 2024. Dr. Patel noted that this may be due to the fact that the parasite does not do well in cooler temperatures.

“In the end … you can refrigerate it,” she continued. “That’s the thing here. If you’ve got cucumbers, got produce, refrigerate it [as] soon as possible because this parasite does not like to have that cool environment.”

Antibiotics can also be used to treat the illness, Dr. Patel said.

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