U.S. officials have traced an explosive diarrhea-causing parasite outbreak in five states to shredded lettuce served at the popular fast-food chainBy Claire Cameron A photomicrograph of a fresh stool sample, which had been prepared using a 10 percent formalin solution and stained with a modified acid-fast stain, revealed the presence of four Cyclospora cayetanensis oocysts in the field of view. CDC/DPDx–Melanie MoserJoin Our Community of Science Lovers!An outbreak of an explosive diarrhea-causing parasite is linked to shredded iceberg lettuce served at the popular Tex-Mex chain Taco Bell in five states, the U.S. Centers for Disease Control and Prevention (CDC) announced.The affected states are Indiana, Kentucky, Michigan, Ohio and West Virginia, the CDC said.The CDC, the U.S. Food and Drug Administration and state public health officials have been investigating the outbreak's source, which so far has sickened thousands of people. In Michigan, one of the worst hit states, officials say there are at least 4,300 cases of cyclosporiasis, an illness caused by a parasite called Cyclospora cayetanensis. It spreads through food or water contaminated with feces.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.The CDC, which has confirmed 1,644 cases and is investigating some 5,100 more, has said its numbers are almost certainly an undercount of the true case numbers nationwide. There have been some 94 hospitalizations so far, but no deaths. Cyclosporiasis symptoms include sudden, watery and occasionally explosive diarrhea—these symptoms usually appear between two days and two weeks after ingesting the parasite. The illness can last anywhere from a few days to a month or longer, according to the CDC."Do not eat shredded iceberg lettuce from Taco Bell locations in Indiana, Kentucky, Michigan, Ohio, and West Virginia," the CDC said in a statement on its website. "CDC is also investigating other outbreaks and illnesses of cyclosporiasis nationally that are unrelated to this outbreak."Taco Bell did not immediately respond to a request for comment.To avoid contracting the illness, the best thing to do is to avoid eating lettuce, gastroenterologist Rabia de Latour told Scientific American. Importantly, washing leaves before you eat them is not enough to get rid of the parasite—that requires cooking food to at least 158 degrees Fahrenheit. The CDC also recommends that people wash their hands and any other fresh produce thoroughly before eating, cutting or cooking it.This is a developing story and may be updated.It’s Time to Stand Up for ScienceIf you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.