A growing outbreak of cyclosporiasis, a parasitic illness that causes severe diarrhea, has spread across more than 20 states in the U.S. this summer, leading to widespread concern and advisories from health departments.
As of July 10, Michigan's health department reported 1,562 cases of cyclosporiasis, with 44 hospitalizations. This marks a significant increase compared to the state's typical annual average of around 50 cases. Ohio has reported 177 infections. While no deaths have been attributed to the current outbreak, the illness can cause debilitating symptoms for up to a month without treatment. The most common symptom is frequent and sometimes explosive watery diarrhea, accompanied by cramping, bloating, nausea, and vomiting. Symptoms typically appear between two days and two weeks after consuming contaminated food.
Cyclosporiasis is caused by the parasite Cyclospora cayetanensis, which infects humans when attached to fresh produce that is then consumed. The parasite does not spread from person to person. Previous outbreaks in the U.S. have been linked to various fresh produce items, including bagged salads, basil, cilantro, peas, and berries.
Identifying the source of the current outbreak has proven challenging. Laina Stebbins, a spokesperson for the Michigan Department of Health and Human Services, stated that no specific grower, supplier, or type of produce has been identified as the source. This difficulty in tracing the outbreak is attributed to the nature of the parasite and the complex, globalized food supply chain.
Dr. Kathleen Linder, a hospital epidemiologist at the Veterans Affairs hospital in Ann Arbor, Michigan, explained that contamination events can occur in tropical or subtropical regions where the parasite is more common, and the produce can then be shipped worldwide. The long incubation period of the parasite, up to two weeks between consumption and symptom onset, further complicates traceback efforts. "Oftentimes when we see these outbreaks, what happens is that somewhere in the world, a contamination event occurs, and then that produce is then shipped throughout the area and it could go anywhere in the world," Linder told Vox.
Joseph Eisenberg, a professor of epidemiology and global public health at the University of Michigan, noted that the reliance on imported produce for year-round availability increases opportunities for contamination. "We’re relying more and more on produce coming from other countries so that we can have raspberries all year round," Eisenberg said. "That kind of luxury only happens when we centralize our food distribution system."
Public health officials recommend several steps to reduce the risk of cyclosporiasis infection. Thoroughly washing raw fruits, vegetables, and herbs under running water before eating or preparing them is crucial. For firmer produce like melons and cucumbers, scrubbing with a produce brush is advised. Damaged or bruised areas on produce should be cut away. Even products labeled as prewashed may benefit from an additional rinse.
Given that previous outbreaks have been linked to bagged salads, consumers might consider purchasing whole heads of lettuce and washing individual leaves. For items like green onions, it is recommended to remove the outer layer and bulbous root before washing. Raspberries, which have been associated with past outbreaks, can be particularly difficult to clean and may be safer to consume cooked or as frozen berries, as freezing is believed to reduce the parasite. Leftovers should be refrigerated within two hours.
Health authorities also suggest considering locally sourced foods, as cyclosporiasis is more prevalent in produce from other regions. Individuals experiencing severe diarrhea should stay well-hydrated. Medical attention is recommended for symptoms such as dizziness, inability to keep fluids down, or very dark urine. Patients with these symptoms should contact their healthcare providers and local health departments.
While experts work to pinpoint the source of the current outbreak, cyclosporiasis remains a recurring concern tied to the modern food system, underscoring the importance of diligent food hygiene practices.