Cyclosporiasis Outbreak 2026: Symptoms, Testing & Treatment

A fast-moving outbreak of cyclosporiasis — an intestinal infection caused by a microscopic parasite that produces weeks of watery, sometimes explosive diarrhea — has become one of the largest the United States has seen in years. This guide, reviewed by a board-certified physician, explains what the parasite is, why it is so easy to miss, how it is correctly diagnosed and treated, and how to protect your household while investigators work to find the source. The live tracker above is updated as the CDC and FDA release new figures.

What Is Cyclosporiasis?

Cyclosporiasis is an intestinal illness caused by the single-celled parasite Cyclospora cayetanensis. People become infected by swallowing food or water contaminated with the parasite — most often fresh produce grown or irrigated in conditions exposed to feces. Importantly, the illness does not spread directly from person to person: freshly passed parasite oocysts are not immediately infectious and need days to weeks in the environment before they can infect someone else, per the CDC.^[5]

The time between infection and illness is usually about one week but can range from as little as 2 days to 2 weeks or more.^[2] That long, variable lag — combined with an estimated six-week delay between when people get sick and when cases are reported to federal authorities — is a major reason outbreaks are hard to trace and why reported case counts lag well behind the true number of infections.

The Parasite — and Why It's So Hard to Wash Off

Understanding one quirk of Cyclospora's biology explains almost everything confusing about this illness: why it isn't contagious, why washing produce doesn't reliably remove it, and why a hot summer drives outbreaks. When the parasite is passed in stool, its egg-like oocysts are not yet infectious. They must spend days to weeks outside a host, in warm, moist conditions, to "sporulate" — to mature into an infectious form.^[8]

This single fact has three practical consequences:

• It's not spread person to person. Because freshly passed oocysts can't infect anyone for days, you cannot catch it from a sick family member the way you catch a norovirus stomach bug — and food handled by an infected cook shortly before serving should not, by itself, cause illness.^[8]
• It thrives in warm months. The days-to-weeks sporulation window is temperature-dependent, which is why the U.S. "cyclosporiasis season" runs May 1 through August 31.^[7]
• Washing can't be trusted to remove it. The oocysts are sticky and environmentally hardy. Laboratory work shows they persist on herb and leafy-green surfaces throughout a growing season, and the CDC states that routine chemical disinfection or sanitizing of food and water is unlikely to kill the parasite.^[4][9] Contamination happens in the field, through feces-tainted irrigation water, and the parasite lodges in the microscopic texture of berries and greens where rinse water doesn't reach.

The one thing that reliably destroys it is heat. Cooking kills Cyclospora; freezing does not. That is why, during an active outbreak with no identified product, cooked produce carries the least risk.

Symptoms: What Cyclospora Feels Like

Cyclospora infects the small intestine. The hallmark symptom is watery diarrhea with frequent, sometimes explosive bowel movements. What sets it apart from ordinary "stomach bugs" is its duration and its pattern: untreated, the illness can last from a few days to a month or longer, and it often follows a remitting-relapsing course — symptoms fade, you think you are better, and then they return.^[2]

Common symptoms, per the CDC clinical overview, include:

• Watery diarrhea (the most common symptom)
• Loss of appetite and unintentional weight loss
• Abdominal cramping, bloating, and increased gas
• Nausea and prolonged fatigue
• Less often: vomiting, body aches, low-grade fever, and other flu-like symptoms

Cyclospora vs. Viral Gastroenteritis ("Stomach Bug")

Most short-lived diarrhea is viral gastroenteritis — the common "stomach bug" caused by norovirus, rotavirus, and similar viruses. Because the early symptoms overlap, cyclosporiasis is frequently mistaken for an ordinary stomach bug, and that mistake matters: a viral illness clears on its own in a day or two, while Cyclospora can grind on for weeks and needs a specific antibiotic to resolve. The distinguishing features below are what separate the two in practice.

The practical takeaway: if watery diarrhea has lasted more than a few days, keeps relapsing, or comes with notable weight loss and fatigue — particularly during this outbreak — do not assume it is a passing stomach bug. That pattern is the signal to seek care and specifically ask about Cyclospora testing. For everyday, short-lived stomach bugs, our viral gastroenteritis treatment guide covers when supportive care is enough and when to see a clinician.

What Your Doctor Is Thinking: The Clinical Reasoning

When a patient describes several days of watery diarrhea, a clinician runs through a mental differential — and in a typical week, Cyclospora would sit low on that list. Most acute diarrhea is viral and self-limited. What moves Cyclospora up the list is a specific combination of clues, and knowing them helps you advocate for the right workup.

The features that raise suspicion:

• Duration and relapse. Diarrhea that has lasted more than about a week, or that improved and then relapsed, is not typical of a viral stomach bug and points toward a parasite.^[1]
• The clinical company it keeps. Prominent fatigue, poor appetite, and unintentional weight loss alongside the diarrhea are classic for cyclosporiasis and unusual for a 24-hour virus.^[1]
• Timing and exposure. Illness during May–August, and any history of eating fresh produce like berries, leafy greens, or fresh herbs, fits the seasonal, produce-borne pattern.
• The outbreak itself. In 2026, a compatible illness is a reason to test even without a known exposure, because a large multistate outbreak is underway.

A clinician also weighs the alternatives that can mimic it — Giardia (another parasite causing prolonged, sometimes relapsing diarrhea and bloating), bacterial causes, and, in anyone recently on antibiotics, C. difficile. The reason this matters to you: several of these, including Cyclospora, are missed unless the clinician specifically orders targeted testing rather than relying on a basic panel.

Why It's Missed: Diagnosis Requires a Specific Test

Here is the single most important thing for patients to understand: Cyclospora is not detected on standard stool tests. Ova-and-parasite testing for Cyclospora requires special stains or laboratory procedures that most U.S. labs do not run routinely, and not all gastrointestinal PCR panels include a Cyclospora target.^[1] If a clinician does not specifically think of it and order the right test, the diagnosis is missed.

Correct testing means asking for one of the following:

• Stool PCR that specifically includes a Cyclospora target (molecular detection of the parasite's DNA)
• Modified acid-fast or "hot" safranin staining, or examination for autofluorescent oocysts under UV microscopy

Two practical caveats from the CDC: a single negative stool specimen does not rule out cyclosporiasis, and patients may need to submit several specimens collected on different days.^[1] If your symptoms fit and the first test is negative, do not assume you are in the clear.

Treatment: What Actually Works

The good news is that cyclosporiasis is highly treatable. The treatment of choice is the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX) — sold as Bactrim, Septra, or Cotrim. The standard regimen for immunocompetent adults, per the CDC, is:^[3]

A few important points on treatment:

• Sulfa allergy: No highly effective alternative to TMP-SMX has been established. Options the CDC describes for people who cannot take it include observation and symptomatic care, an antibiotic with only limited supporting data, or supervised desensitization — the last only for selected patients evaluated by an allergist who do not have a life-threatening allergy.^[3] This is a decision to make with a clinician.
• Anti-diarrheal medicines such as loperamide (Imodium) may ease symptoms but do not cure the infection — the parasite still needs the antibiotic to clear.
• Rehydration matters. Weeks of diarrhea can cause meaningful fluid and electrolyte loss; oral rehydration is an important part of supportive care.

Prevention: Protecting Your Household

Because no contaminated product has been identified and no recall issued, there is no single item to avoid. Prevention therefore rests on safe produce handling. The most important thing to understand is that washing reduces risk but does not reliably remove Cyclospora. The CDC notes that routine chemical disinfection or sanitizing of food and water is unlikely to kill the parasite, and its oocysts can lodge in the surfaces and crevices of produce such as berries and leafy greens.^[4] Cooking is the only reliable way to kill it — heat destroys Cyclospora, while freezing does not.

Practical steps drawn from CDC guidance:^[4]

• Wash hands with soap and water before and after handling or preparing raw fruits and vegetables.
• Wash all fruits and vegetables thoroughly under running water before eating, cutting, or cooking — even if you plan to peel them. (Produce labeled "prewashed" does not need re-washing.)
• Scrub firm produce such as melons and cucumbers with a clean produce brush.
• Cut away damaged or bruised areas before preparing.
• When you want the most certainty during an active outbreak, favor cooked produce — heat is the one method confirmed to destroy the parasite.

Historically, U.S. cyclosporiasis outbreaks have been repeatedly linked to categories of fresh produce including raspberries, basil, cilantro, snow peas, mesclun lettuce, and bagged salads. During the 2026 investigation, some state health officials have noted lettuce and salad greens recurring in their case interviews, but investigators have not confirmed any grower, supplier, or product.^[6]

High-Risk Foods: What Three Decades of Outbreaks Tell Us

Because investigators have not identified the 2026 source, the most useful guide to risk is history. Since the mid-1990s, U.S. cyclosporiasis outbreaks have clustered around a predictable set of fresh, raw produce categories — almost always items eaten uncooked and, historically, often imported from regions where the parasite is endemic.^[10] The recurring culprits are fresh berries (especially raspberries), fresh herbs (basil, cilantro), leafy greens and bagged salads, and snow peas.

Two patterns stand out. First, the vehicle is almost always eaten raw — cooking would have prevented these outbreaks. Second, even careful traceback frequently fails to pin down a single farm; in the large 2020 bagged-salad outbreak, the FDA completed its traceback but could not conclusively confirm the source.^[12] That is exactly the situation in 2026, and it is why individual food-handling choices — not a recall — are your main protection right now.

Recovery, Relapse, and What to Expect After Treatment

For most people who are not immunocompromised, the outlook is good. Once the correct antibiotic is started, symptoms typically ease within a few days, though full recovery of energy and appetite can take longer after a prolonged illness. The critical point is that the infection does not reliably clear on its own: untreated, it can persist or relapse in waves for a month or more, which is why testing and treatment shorten what would otherwise be a miserable, drawn-out course.^[1]

A few things to expect and watch for:

• Finish the full course. Complete the entire 7–10 day TMP-SMX course even after you feel better, and tell your clinician if diarrhea returns after treatment — some patients, especially those with weakened immune systems, need a longer course.^[3]
• Rehydrate throughout. Weeks of diarrhea deplete fluids and electrolytes; oral rehydration solutions are more effective than water alone for replacing what's lost.
• Lingering gut symptoms such as bloating or irregular bowel habits can persist briefly after any prolonged intestinal infection; new or worsening symptoms warrant a re-check.

Where to Get Care: Telehealth, In-Person, or the ER

Cyclosporiasis is, for most healthy adults, an outpatient illness — but knowing the right door to knock on saves time and worry.

Because Cyclospora requires a specific stool test and a specific antibiotic — neither of which is part of routine self-care — a prolonged or relapsing illness is genuinely worth a visit rather than waiting it out. A synchronous video visit with a physician is an efficient way to get the right test ordered and, when appropriate, treatment prescribed.

Who Is Most at Risk

Anyone can be infected. Most otherwise healthy people recover, with or without treatment, though the illness can drag on for weeks. Because prolonged diarrhea causes dehydration, it can be more serious for older adults, young children, and people who are immunocompromised. People living with HIV, in particular, may experience more severe or prolonged illness and can require longer antibiotic courses.^[3] In the 2026 outbreak, the CDC reports cases spanning ages 5 to 88, with a median age of 44.^[7]

When to See a Doctor

Contact a clinician if watery diarrhea lasts more than a few days, keeps returning after seeming to improve, or comes with significant weight loss, dehydration, or profound fatigue — and specifically mention the outbreak and ask about Cyclospora testing. Seek urgent in-person care for signs of severe dehydration (dizziness, very little urine, rapid heartbeat), high fever, bloody stools, or an inability to keep fluids down.

Frequently Asked Questions