Public health officials have declared that imported broccoli was behind an outbreak from the Cyclospora parasite, but have closed their investigation without determining exactly wher the produce came from.

The Food and Drug Administration announced that the outbreak has been determined to be over. The FDA reported that the U.S. Centers for Disease Control and Prevention, along with state and local officials, all concur that the outbreak has ended. 

Twenty patients were confirmed as having been infected by the microscopic parasite Cyclospora, but their home states and ages have not been reported.

The outbreak was first reported by the FDA on May 24. The CDC has not posted any information about the outbreak.

During interviews with public health investigators, infected people reported eating broccoli before becoming sick.

“FDA and state and local partners conducted traceback investigations and determined that the product of interest was imported broccoli,” according to the agency’s outbreak updat on June 21.

Broccoli was not named during the outbreak investigation as a cause of illnesses and no recall was initiated.

The FDA reported that it was unable to determine exactly wher the broccoli came from or who produced it. The agency did not report what producers’ or importers’ broccoli was traced, but did say that none of the samples collected came back positive for the outbreak strain of Cyclospora cayetanensis.

Although the investigation has been closed and the outbreak determined to be over, additional patients could be identified because of the nature of Cyclospora infection. People who are infected can have long-lasting symptoms. They can also appear to have recovered but still have the infection with recurring symptoms.

Specific testing is required to diagnose Cyclospora infections because illnesses caused by the parasite can mimic other illnesses. Antibiotics are required to kill the parasite.

Anyone who has developed symptoms of Cyclospora infection, and has reason to believe they have been exposed to the parasite, should seek medical attention.

Cyclospora infection can cause severe abdominal pain, watery diarrhea, nausea, vomiting, body aches, and fatigue. Symptoms can develop between two and 14 days after exposure. Though symptoms can be severe enough to send people to the hospital, it’s rare for people to die from Cyclospora infections. 

Cyclospora is a type of protozoa, which is a tiny, single-celled organism. It is transmitted when people somehow ingest microscopic amounts of contaminated feces, typically through contaminated food or water. It can be spread only through human waste, unlike E. coli and salmonella, which can also be spread from animal fecal matter. 

In the U.S., imported produce is a common source of cyclospora. Food safety experts say there’s no evidence that washing produce will remove the parasite.