The parasite can cause weeks of watery diarrhea and is often linked to contaminated food or water. Officials are still investigating the source as case counts climb across much of the United States.
Cyclosporiasis cases have risen by thousands in the United States, and the outbreak has reached 45 states, with the CDC tracking 6,707 laboratory-confirmed infections since May 1, USA TODAY reported, citing federal counts. The illness is caused by the Cyclospora parasite — the “explosive diarrhea parasite” in recent headlines — and the CDC is tracking the outbreak as a multistate investigation.
That matters now because cyclosporiasis can cause watery, sometimes frequent diarrhea that lasts for weeks, fades, then comes back. It is not usually life-threatening, but the CDC says it can make some people very sick.
Why 45 states matters
A parasite outbreak across 45 states is not the same kind of threat as a fast-spreading respiratory virus. Cyclospora usually spreads when people consume food or water contaminated with the parasite, not through ordinary close contact.
Still, the breadth of the outbreak makes it hard to dismiss as a small local cluster. When cases appear across most of the country, investigators have to consider widely distributed foods, overlapping supply chains, travel history and the possibility that more than one source is involved.
The CDC says state and federal partners are working together to investigate the current multistate outbreak, and that efforts to identify the source or sources of illness are ongoing. That means the case count is clearer than the cause.
The 6,707 figure also reflects laboratory-confirmed infections. The real number of illnesses may be higher because many people with diarrhea never seek care, and testing for Cyclospora is not always part of routine stool testing.
What Cyclospora does
Cyclosporiasis is a gastrointestinal illness caused by the microscopic Cyclospora parasite. According to the CDC, people can become infected by consuming food or water that contains the parasite.
Once inside the body, Cyclospora infects the small intestine. Symptoms can include watery diarrhea that may be frequent, along with a pattern that is especially frustrating: symptoms can seem to improve, then return one or more times.
The incubation period is another reason outbreaks can be difficult to untangle. The CDC says the time between infection and illness is usually about one week, but it can range from two days to two weeks or more.
That delay can make it hard for patients to remember what they ate, where they traveled or which meal might have been the source.
Why the source is elusive
In the United States, cyclosporiasis outbreaks have been linked to various types of fresh produce. The CDC has not identified a specific source in the current outbreak, based on the information made public in its current cyclosporiasis materials.
That uncertainty is important. Without a named food item, brand, farm, restaurant chain or distributor, there is no simple recall-style action for consumers to take. Public health officials instead have to build a case from interviews, lab results and patterns across states.
Another wrinkle: direct person-to-person transmission is considered unlikely. The CDC says Cyclospora needs at least one to two weeks in the environment after being passed in a bowel movement before it becomes infectious.
That makes this different from many stomach bugs that can race through a household or workplace. The risk is more about contaminated food or water somewhere before consumption than about catching it from a sick coworker the next day.
Symptoms that deserve attention
The headline symptom is diarrhea, but the concern is duration and recurrence. Untreated cyclosporiasis can last from a few days to more than a month, the CDC says, and symptoms may relapse.
Persistent diarrhea can also lead to dehydration, especially in children, older adults and people with existing health problems. People with weakened immune systems may be at higher risk for severe or prolonged illness.
Anyone with severe diarrhea, bloody stool, signs of dehydration, fever that does not improve, or symptoms lasting more than a few days should contact a health care provider. This is especially true if they recently ate fresh produce, traveled, or live in an area reporting cases.
Diagnosis requires a stool test, but there is a catch: the CDC says identifying Cyclospora requires special laboratory testing that may not be included in routine stool exams. Patients may need to provide multiple samples on different days.
Treatment is available
Cyclosporiasis is treatable. The CDC lists trimethoprim-sulfamethoxazole, sold under names including Bactrim, Septra or Cotrim, as the standard treatment.
People who are allergic to sulfa drugs should talk with their health care provider about possible options. Rest and fluids also matter because diarrhea can drain the body quickly.
Some healthy people recover without treatment, but that does not mean the illness is harmless. Weeks of recurring diarrhea can disrupt work, travel, caregiving and basic daily life, even when a person is not in immediate danger.
The practical message is not to self-diagnose every stomach upset as cyclosporiasis. It is to make sure persistent symptoms are evaluated, and to mention Cyclospora specifically if the pattern fits.
What consumers can do now
With no single source identified, prevention advice is broad rather than dramatic. The CDC recommends safe food-handling practices to reduce the risk of illness.
- Wash hands before preparing or eating food.
- Rinse fresh produce under running water when appropriate.
- Keep raw foods separated from foods that are ready to eat.
- Refrigerate perishable foods promptly.
- Clean cutting boards, knives and counters after food prep.
Those steps cannot guarantee protection from every produce-linked parasite outbreak, especially if contamination happened before food reached a kitchen. But they reduce risk and help prevent other foodborne illnesses as well.
The harder takeaway is that “fresh” does not always mean risk-free. Produce remains an important part of a healthy diet, but outbreaks like this show why surveillance, farm-level sanitation, distribution tracking and fast public communication matter.
What remains unknown
The biggest unanswered question is the source. The CDC says investigations are ongoing, which leaves consumers and clinicians working with symptoms, geography and lab testing rather than a clear product warning.
It is also unclear how much the confirmed count underestimates the true spread. Because testing can be missed and symptoms may come and go, some cases may never make it into official numbers.
For now, the story is less about panic than persistence: thousands of confirmed cyclosporiasis cases, 45 states, and a parasite that can linger long enough to be mistaken for an ordinary stomach bug. The best move is to take prolonged diarrhea seriously, practice careful food handling and watch for updates as investigators narrow the source.
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