Mystery Diarrhea Parasite Sweeps 34 States

A microscopic parasite is tearing through 34 states in 2026, and investigators still cannot find what food is carrying it.

Story Snapshot

The Centers for Disease Control and Prevention (CDC) confirmed 1,645 cases of cyclosporiasis across 34 states as of July 13, 2026, with more than 5,100 additional cases still under review.
Michigan alone reported over 1,500 cases, making it the largest such outbreak in state history.
The parasite spreads through contaminated food or water, not person-to-person contact, but investigators have not yet identified the food source.
Symptoms can last weeks and include explosive watery diarrhea, cramping, nausea, and severe fatigue — but no deaths have been reported.

What Cyclospora Actually Is

Cyclospora cayetanensis is a single-celled parasite too small to see without a microscope. When you eat or drink something contaminated with it, the parasite infects the lining of your small intestine. The illness it causes is called cyclosporiasis. It is not a virus or a bacterium. It is a protozoan, which puts it in the same broad family as the parasite that causes malaria. That matters because it behaves differently from most foodborne bugs — and it is far harder to track down.

Symptoms That Can Last for Weeks

Most foodborne illnesses hit hard and fade within a few days. Cyclospora does not work that way. Symptoms typically start one to two weeks after exposure. They include frequent, sometimes explosive watery diarrhea, stomach cramps, bloating, nausea, vomiting, fatigue, and weight loss. Without treatment, symptoms can drag on for weeks or even months, cycling in and out. The antibiotic combination trimethoprim-sulfamethoxazole is the standard treatment, but doctors have to think to test for it first — and many do not.

That diagnostic gap is part of why outbreaks grow so large before anyone notices. Standard stool tests do not detect Cyclospora. Labs need a specific microscopy technique using ultraviolet light to spot the parasite’s oocysts, which are the tiny egg-like forms it sheds. Many clinics never order that test unless a doctor specifically requests it. That means thousands of sick people likely never get a confirmed diagnosis, which is exactly what the CDC’s own data hints at — more than 5,100 cases were still awaiting confirmation as of mid-July 2026.

How It Spreads — and How It Does Not

Cyclospora spreads only one way: you ingest something contaminated with human feces that contains the parasite’s oocysts. You cannot catch it from another person directly. The oocysts must spend time maturing outside the body before they become infectious, which rules out person-to-person spread entirely. Past U.S. outbreaks have been traced to fresh imported produce like raspberries, cilantro, basil, snow peas, and bagged salad mixes. A 2023 outbreak in Alabama was tied to cilantro at a single restaurant.

Why the 2026 Outbreak Is Different

Every summer, the U.S. sees a seasonal rise in Cyclospora cases, mostly linked to imported fresh herbs and produce. This year is different in scale and in mystery. Michigan typically reports around 50 cases per year. By early July 2026, it had logged over 1,500. The states with the most cases are Michigan, Illinois, New York, and Texas. Yet despite weeks of investigation by the CDC, the U.S. Food and Drug Administration (FDA), and state health agencies, no single food source, grower, or supplier has been identified.

Heads up! 🚨 A parasitic stomach bug is spreading fast across the US.

The CDC reports a sharp surge in Cyclosporiasis cases—already hitting 1,645 confirmed infections across 34 states since May, with over 5,100 more under investigation.
This nasty parasite causes watery…

— Jeblyn (@Jeblyn234) July 15, 2026

That failure to find a source is not just frustrating — it means no food recall is possible. Without knowing what food is contaminated, health officials cannot pull it from shelves. They can only tell the public to be careful. The parasite resists standard chemical disinfection, and washing produce alone does not reliably remove it. Cooking fresh greens to an internal temperature of at least 158 degrees Fahrenheit kills the parasite, but that is not practical for salads, fresh herbs, or raw fruit. The honest answer right now is that investigators do not yet know what to tell people to avoid.

What You Can Do Right Now

Cook any produce you can. Rinse everything else under running water, even if the bag says pre-washed. Avoid raw fresh herbs like cilantro and basil if you are in a high-case state and are immunocompromised, elderly, or pregnant. If you develop persistent watery diarrhea lasting more than a few days, tell your doctor you want to be tested specifically for Cyclospora — do not assume a standard stool test will catch it. Early treatment shortens the illness significantly. Left untreated, it can sideline you for a month or more.