A gastrointestinal parasite is quietly spreading across the country, and most people who get sick don't even know what hit them.
Cyclospora cayetanensis is an explosive diarrhea-inducing parasite that, at the time of this writing, has been confirmed in cases in 31 states, sickening hundreds and sending dozens to the hospital—yet the source remains unidentified. Here's what you need to know to protect yourself.
What is the Cyclospora outbreak?
A gastrointestinal parasite called Cyclospora is spreading across the United States, with confirmed cases now reported in at least 31 states. As of Tuesday (July 14), the Centers for Disease Control and Prevention had logged 1,645 confirmed domestic cases of cyclosporiasis, but there are an estimated 7,000 cases in the country so far.
Michigan is the outbreak's epicenter, accounting for more than 3,000 cases. State health officials there have pointed to lettuce and salad greens as a potential source, though no specific produce, grower, or distributor has been confirmed.
What is Cyclospora, and how does it spread?
Cyclospora cayetanensis is a microscopic, single-celled parasite that infects the small intestine and can only be detected under a microscope. It spreads through a straightforward but easily overlooked route: ingesting food or water contaminated with feces carrying the parasite's oocysts.
Fresh produce is the most common vehicle because the parasite can survive on raw fruits and vegetables that have been irrigated or washed with contaminated water.
One thing worth knowing is that Cyclospora can't pass directly from person to person the way a cold does.
After the parasite is shed in a bowel movement, it needs days to weeks in the environment before it becomes infectious, which means casual contact with a sick person poses little risk. That delay also helps explain why outbreaks often trace back to a shared food source rather than a cluster of people who were simply in the same room.
Symptoms typically appear about a week after exposure, though the window runs anywhere from two days to more than two weeks.
What are the symptoms of Cyclosporiasis?
The hallmark symptom of Cyclosporiasis is watery, sometimes explosive diarrhea, typically accompanied by stomach cramps, nausea, bloating, and fatigue.
Most people start feeling sick within a week of ingesting the parasite, though the window runs anywhere from two days to two weeks or longer. Some infected people experience no symptoms at all, particularly in regions where Cyclospora is common. For those who do get sick, the illness can be disruptive.
Without treatment, symptoms don't just fade on their own quickly. Cyclosporiasis is known for dragging on far longer than a typical stomach bug, with recurring bouts of diarrhea that can last weeks if left unaddressed. That persistence is one reason doctors recommend seeking care promptly rather than waiting it out.
Who is most at risk?
The CDC hasn't published a breakdown of Cyclosporiasis hospitalizations by age group for the 2026 outbreak, but the pattern from prior years and from parasitic gut infections broadly is consistent: young children, adults over 65, and people with weakened immune systems face the steepest risk of serious illness.
For those groups, the watery diarrhea and prolonged cramping that Cyclospora causes can accelerate dehydration faster than the body can compensate, pushing a miserable-but-manageable illness into territory that requires IV fluids and medical monitoring.
Immunocompromised individuals, like those with HIV, undergoing chemotherapy, or recipients of transplants on immunosuppressants, Cyclospora infections can persist for months without treatment and cause severe, relapsing illness, and treatment often needs to be longer and more closely supervised.
Healthy adults, meanwhile, typically clear the parasite with a standard course of the antibiotic trimethoprim-sulfamethoxazole.
If you or someone in your household falls into any high-risk categories and develops prolonged diarrhea, fatigue, or signs of dehydration, a call to a doctor—rather than a wait-and-see approach—is the right move.
What is the source of the outbreak?
Investigators haven't exactly pinned down the source of Cyclospora yet, but lettuce and salad greens are believed to be related.
Past outbreaks of the parasite in the U.S. and Canada have been traced back to a recognizable roster of fresh produce: bagged salad mixes and kits containing romaine, iceberg lettuce, red cabbage, and carrots; raspberries; fresh cilantro; fresh basil; snow peas; and green onions.
How can you avoid getting sick? Prevention and food safety tips
Until investigators name a specific food source, the safest move is to treat any fresh produce as a potential risk and handle it accordingly. Wash all raw fruits and vegetables thoroughly under running water before eating, cutting, or cooking them. This goes for pre-bagged salads too.
Cooking produce to an internal temperature of 140 degrees Fahrenheit kills Cyclospora, so lightly cooked vegetables are a lower-risk option if you're in an affected area and want extra peace of mind.
For produce you're eating raw, skip the pre-cut bagged blends and opt for whole heads of lettuce you wash yourself. Dry produce thoroughly after rinsing, since moisture helps pathogens survive longer on surfaces. Wash your hands with soap and water before and after handling any fresh produce, and sanitize cutting boards and prep surfaces that contact raw greens.
How is Cyclosporiasis treated?
The good news is that Cyclosporiasis responds well to antibiotics when caught and treated promptly. The standard treatment is trimethoprim-sulfamethoxazole — commonly sold as Bactrim or Septra — taken in one double-strength tablet twice daily for seven to ten days.
Antibiotic treatment makes a real difference. Without it, the illness can drag on for weeks, with symptoms appearing to clear up before cycling back. With treatment, that cycle typically breaks. Fatigue can linger even after diarrhea resolves, sometimes affecting daily function for weeks.
When should you see a doctor?
The clearest signal to call a doctor is when diarrhea that lasts more than a few days, intensifies, or keeps you from staying hydrated. Dehydration moves quickly when you're losing fluids through persistent watery diarrhea, and the warning signs are ones to take seriously: dry mouth, dark urine, dizziness, or feeling significantly weaker than the illness alone would explain. Children and older adults hit those thresholds faster, so the bar for seeking care should be lower for them.
Why did it take so long to detect the outbreak?
Part of the answer may lie in a quiet bureaucratic decision made more than a year before this outbreak drew national attention.
On July 1, 2025, the CDC scaled back FoodNet, its Foodborne Diseases Active Surveillance Network, stripping the program down to monitoring just two pathogens: Salmonella and Shiga toxin-producing E. coli.
Cyclospora was among the six pathogens dropped from required tracking across the 10 states that participate in FoodNet. The change wasn't publicly announced, and it surfaced only after NBC News reported it in August 2025. Dr. J. Glenn Morris, director of a food safety program, put it plainly in a statement.
"Essentially, CDC is backing off on one of their best surveillance systems,” Morris said.
