As if we needed one more thing to worry about so soon after the hantavirus scare, there is a new public health threat for Americans to contend with: a rapidly escalating outbreak of, of all things, diarrhea.
It’s a parasite-borne illness called cyclosporiasis. It can cause explosive and watery bowel movements — and it is wreaking havoc across the United States this summer.
How bad exactly? As of July 15, Michigan’s health department is reporting 3,762 cyclosporiasis cases, up from 1,500 late last week. Forty-four people have been hospitalized as of July 9. To put that number in context, the state normally sees about 50 cases in a year. To the south, at least 364 people have been infected in Ohio. According to a USA Today compilation of state health department data, almost every state has reported at least one cyclosporiasis case this year.
This is not our first bout with a cyclosporiasis outbreak. In 2013, the US saw more than 600 cases, and more than 500 people were sickened across the country by contaminated McDonald’s salad meals in 2018. Cyclosporiasis is caused by the parasite cyclospora, which can infect people when it is attached to fresh produce and then consumed. It does not, fortunately, spread from person to person. We do know some likely culprits: Bagged salads, basil, cilantro, peas, and berries have been linked to prior outbreaks.
Watery diarrhea — described by public health authorities as “frequent” and “sometimes explosive” — is the most common symptom. People can also experience cramping, bloating, nausea, and vomiting. Symptoms can start anywhere between two days and two weeks after a person eats tainted food. No one has died, and thankfully, cyclosporiasis is rarely fatal. But it is an extremely unpleasant experience that could last for up to a month without treatment, and certain people, such as folks who are immunocompromised, are at higher risk of more serious complications.
There are steps that everyone can take to protect themselves from cyclosporiasis (more on that in a moment). But the current situation is challenging, because, right now, officials don’t actually know which products are causing the outbreak. “At this time, no specific produce grower, supplier, or type of produce has been identified as the source,” Laina Stebbins, a spokesperson for the Michigan Department of Health and Human Services, said in a statement to Vox on Friday. On Monday, Michigan officials said they believed lettuce or bagged salad products were to blame, but still had not identified specific brands or items that could be linked to the growing outbreak.
It’s a public health mystery, one that results from both the sneaky nature of the parasite itself and our increasingly globalized food supply. It could be a while before we learn the answer. But, in the meantime, if you’ve found yourself spooked by some of the recent headlines, here’s what you actually need to know.
Why cyclosporiasis outbreaks are so hard to trace
Cyclosporiasis makes itself hard to find. Scientists don’t know exactly how much of the parasite a person needs to be exposed to to become infected — one of many unknowns about the basic features of the bug. The foods carrying this pathogen may not be contaminated with much of it at all, which makes any preemptive testing a challenge.
And, on top of that, there can be a long gap between the parasite being introduced to the food supply and when a person actually gets sick, which further complicates any efforts to trace the outbreak’s origins. A fruit or vegetable could be contaminated in one of the various tropical or subtropical regions of the world where cyclosporiasis is more common, well before it lands in your grocery store in the United States.
“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,” Dr. Kathleen Linder, the hospital epidemiologist at the Veterans Affairs hospital in Ann Arbor, Michigan, told Vox.
Sometimes, the source can be closer to home: A 2020 outbreak appeared to be linked to produce grown in Florida and shipped to a plant in Illinois that produced bagged salad kits. But, as if to demonstrate the difficulty of doing this work, the FDA said it could not conclusively prove those farms were the source of the outbreak.
The point is: We have a food production supply chain that sources produce and combines ingredients from all over the country and the globe — providing more opportunities for a parasite like this to find its way in.
“We’re relying more and more on produce coming from other countries so that we can have raspberries all year round,” Joseph Eisenberg, a professor of epidemiology and global public health at the University of Michigan, told Vox. “That kind of luxury only happens when we centralize our food distribution system.”
Even once an outbreak is underway, it can be hard to pinpoint the source. Symptoms may not occur for up to two weeks after a person eats contaminated food.
“I can barely remember what I had for dinner a couple nights ago; there’s no way I’m going to be able to remember a week ago,” Linder told me. “It takes a lot of time and a lot of manpower to get all that information collected.”
As with any outbreak under the Trump administration, the Centers for Disease Control and Prevention is responding with significantly fewer workers and resources than it used to have. To be clear: This cyclosporiasis outbreak could have happened either way. This parasite has sparked widespread infections before. But Linder said that because the CDC has rolled back some of its national reporting programs, it’s been left to the states to take the lead — and that has made it harder to pull together a complete picture of the outbreak.
“It has been very hard to get updated information,” Linder said. “The information is lagging a little bit behind because it’s being done at the state level.”
What you can do to reduce your risk of cyclosporiasis
For scientists, the work ahead involves better understanding the properties of the pathogen itself and developing surveillance tools and techniques that allow us to catch contaminated food before it reaches people. But what can the rest of us do right now, during an active outbreak?
According to various public health authorities, the short version is to cook the produce that you can — heat is the absolute best option for eliminating cyclosporiasis — and to clean your raw fruits, vegetables and herbs as thoroughly as possible.
Wash everything with running water before eating or preparing it. Scrub the firmer fruits, like melons and cucumbers, with a produce brush if you have one. If you see damaged or bruised areas on your fruit or lettuce, cut them away. Even if a food’s package says it’s prewashed, Linder said she advises people to rewash it just to be sure.
Previous outbreaks have specifically been linked to bagged lettuce and salads, so you might consider buying whole heads of lettuce instead. If you do that, cut away the outer layers and then separate the inner leaves to wash them. For green onions, you should cut away the bulby root and the outer layer and then wash them thoroughly. Raspberries were associated with one of the first US outbreaks in the 1990s, and they are particularly tricky to clean given their bumpy surfaces; you may want to consider eating them only after cooking (to prepare a jam or compote, for example) or opt for frozen raspberries for the time being. (Freezing is believed to reduce, if not completely eliminate, the parasite.) And be careful with leftovers: You should refrigerate any unused foods that you plan to eat later within two hours.
You could also consider buying locally sourced foods, Linder said, because cyclosporiasis is more common in food sourced from other parts of the world.
If you do start to experience extreme diarrhea, make sure to hydrate very well to avoid dehydration. Linder told me that if somebody experiences dizziness, they can’t keep fluids down, or they have very dark urine, then they should seek immediate medical attention. And anybody experiencing those symptoms should get in touch with their health care providers and their local health department.
Sooner or later, experts will probably figure out what caused the current outbreak, whether it’s one source or several. But cyclosporiasis will still be a concern in the future; it’s a byproduct of the food system we have built. It serves as a potent reminder about the importance of good food hygiene. A little extra effort to wash your food before you eat it could save you a lot of pain later.
Update, July 15, 2026, 11:45 am ET: This story, first published July 10, has been updated with current case numbers and products linked to the outbreak.