How to Avoid Getting Cyclosporiasis and Why Washing Lettuce May Not Be Enough

As cases of an explosive diarrhea-causing parasite continue to rise in the United States, lettuce-based salads may be taken off the table until the source is found.

Cyclosporiasis is a disease caused by the parasite Cyclospora cayetanensis, which can be spread through food or water. A cyclospora infection can cause severe diarrhea and “sometimes explosive stools.” according to the U.S. Centers for Disease Control and Prevention (CDC).

In Michigan, the state hardest hit by the current outbreak, 3,762 cases had been reported as of Wednesday, including 44 requiring hospitalization as of July 9. Nationally, the picture is bleaker. As of July 13, the CDC reported receiving 1,645 case reports in 34 states, including 141 hospitalizations. However, the very next day, the agency issued a statement acknowledging that the true number of cases is likely much higher, adding that 5,100 cases require further analysis to confirm a diagnosis of cyclosporosis.

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“CDC and state and federal partners are working together to investigate multiple outbreaks of cyclosporiasis,” the release said. “Investigations to identify and confirm the sources of the outbreaks are ongoing.”

The source of the outbreak is also unclear. Michigan health officials said the two-week incubation period between infection and the appearance of symptoms, along with the complexity of food distribution networks in the United States, made it difficult to track the source, but some signs suggest that lettuce may be involved.

Anyone concerned about this very unpleasant disease should avoid lettuces for the time being, says Rabia de Latour, a gastroenterologist at the NYU Grossman School of Medicine. Washing produce alone “is not going to eliminate this problem as a foolproof method,” she adds.

“The only way to really kill this parasite from food is to cook it to 158 degrees Fahrenheit,” she says.

Health authorities also warned against using pre-washed and bagged lettuce in particular, and advised consumers to instead buy whole heads of lettuce and discard the outer two or three layers before carefully washing what’s left.

De Latour says this advice might be somewhat effective, but would not completely prevent infection.

“Washing is good. Washing with a vegetable brush is even better, but you still can’t say with certainty that you have removed and/or killed the parasite with this method,” she says.

So far, no deaths have been linked to the outbreak and cyclospora is not generally known to be fatal to humans. The disease can also be treated to some extent with a medication called trimethoprim-sulfamethoxazole (TMP-SMX), which helps prevent the parasite from synthesizing the folic acid it needs to live and reproduce.

However, De Latour says people with serious comorbidities, such as heart or kidney disease, could be at risk of death due to the dehydration that results from diarrhea, but added that the extremely unpleasant nature of the symptoms should be enough to make the general public cautious about what they eat.

“It’s called explosive diarrhea for good reason. People are distressed and need to be near the toilet. They can lose weight and feel really crummy.”