Parasite causing severe diarrhea spreads across the United States (What you need to know to protect yourself)

A microscopic parasite capable of causing prolonged and sometimes explosive diarrhea is spreading across the Usurveillance while investigators search for the contaminated food source behind the rapidly growing number of illnesses.

The infection, known as cyclosporiasis, is caused by Cyclospora cayetanensis, a single-celled parasite that attacks the intestinal tract. Although the disease is not usually fatal, it can leave patients suffering from relentless watery diarrhea, severe fatigue, abdominal cramping, nausea, appetite loss and potentially dangerous dehydration for weeks.

As of July 9, 2026, the U.S. Centers for Disease Control and Prevention had received reports of 843 laboratory-confirmed domestically acquired cases across 31 states. At least 86 patients had been hospitalized, and more than 1,500 additional cases were awaiting analysis to determine whether they met the federal definition for domestically acquired cyclosporiasis. No deaths had been reported. national figures do not tell the entire story.

State health departments may include both confirmed and probable cases, while the CDC’s total includes only laboratory-confirmed infections formally submitted to its surveillance program. The agency has warned that a reporting delay of approximately six weeks means the true scale of the outbreak may be substantially larger than the published federal count. emerged as the center of the crisis. On July 13, state officials reported 2,640 cases associated with the outbreak, an increase of more than 1,000 cases since the previous update. Forty-four Michigan patients were known to have been hospitalized. Investigators said lettuce or other salad greens were being examined as a possible source, although no specific grower, supplier or produce product had been definitively identified. Dr. Armor, the rising numbers should be taken seriously without causing unnecessary panic.

“The greatest danger is not that this parasite is instantly deadly,” Dr. Armor explained. “The danger is that people may dismiss the illness as ordinary food poisoning, continue losing fluids for days or weeks and seek medical attention only after severe dehydration has already developed.”

A Parasite Hidden in Food and Water

People become infected after consuming food or water contaminated with Cyclospora. The parasite has historically been associated with fresh produce that is commonly eaten raw, including raspberries, basil, cilantro, snow peas, mesclun lettuce and packaged salad mixtures. have not yet linked the broader 2026 increase to one common product. The FDA was investigating several separate Cyclospora clusters in early July, with traceback work underway for products that had not yet been identified publicly. nty makes the investigation particularly difficult. Unlike an outbreak connected quickly to a single restaurant or packaged item, cyclosporiasis cases can appear across multiple jurisdictions, involve different food distribution networks and take days or weeks to recognize.

The supplied outbreak briefing also emphasizes the parasite’s connection to raw produce, the difficulty of detecting it through routine testing and the risk of dehydration among older adults and medically vulnerable patients.

Cyclospora also behaves differently from highly contagious stomach viruses such as norovirus. When an infected person passes the parasite in feces, it is not immediately capable of infecting another person. The parasite must remain in the environment long enough to mature before it becomes infectious.

As a result, direct person-to-person transmission is considered unlikely. Living with, hugging or caring for a patient with cyclosporiasis does not normally spread the illness in the way that norovirus can sweep through households, hospitals or nursing homes.

“This is an important point for families,” Dr. Armor said. “You should maintain excellent hand hygiene and safely clean bathrooms, but you do not need to isolate a patient as though the infection were spreading through the air or through ordinary physical contact.”

Symptoms May Disappear and Then Return

The most recognizable symptom is frequent watery diarrhea, which may become severe or explosive. Other symptoms can include abdominal cramping, bloating, increased gas, nausea, vomiting, loss of appetite, weight loss, headaches, muscle aches and overwhelming fatigue.

Symptoms usually begin about one week after exposure, although the incubation period may range from approximately two days to two weeks. That delay creates a major obstacle for investigators because patients may struggle to remember everything they ate during the previous 14 days. acterial foodborne illnesses that strike quickly and resolve within a day or two, untreated cyclosporiasis can continue for a month or longer. Patients may temporarily feel better, only for diarrhea and exhaustion to return.

Dr. Armor said that pattern should be treated as a warning sign.

“If diarrhea lasts more than several days, repeatedly improves and returns, or is accompanied by weight loss and severe weakness, do not assume it is a routine stomach virus,” he advised. “Contact a healthcare provider and mention Cyclospora specifically.”

People with healthy immune systems may eventually recover without medication, but the illness can be prolonged. Patients with weakened immune systems may face more severe or persistent symptoms. ation Is the Main Immediate Threat

The parasite itself is only part of the medical concern. Prolonged diarrhea removes water and electrolytes from the body, potentially leading to dizziness, low blood pressure, confusion, kidney injury and falls.

Older adults are particularly vulnerable because they may already have reduced kidney function, diabetes, heart disease or medications that affect fluid balance. Young children, pregnant patients, cancer patients and people with weakened immune systems also deserve closer observation.

Warning signs of significant dehydration include a dry mouth, very dark or reduced urine, dizziness when standing, rapid heartbeat, confusion, unusual sleepiness, inability to keep liquids down and severe weakness.

“In an older patient, dehydration can become a chain reaction,” Dr. Armor explained. “The patient becomes dizzy, falls, fractures a hip and suddenly loses the independence they had before the infection. That is why early attention matters.”

People who cannot drink enough to replace lost fluids, appear confused, faint, experience severe abdominal pain or show signs of kidney trouble should receive urgent medical assessment.

Oral rehydration fluids containing electrolytes may be more useful than plain water when diarrhea is persistent. Patients with heart failure, kidney disease or other conditions requiring fluid restrictions should ask a clinician how much fluid is safe.

Routine Tests May Miss the Infection

Cyclospora can be difficult to diagnose. A routine stool examination may not automatically include testing for the parasite, and patients can shed it intermittently. A single negative sample therefore does not always exclude infection.

The CDC states that special laboratory testing is required and that patients may need to submit several stool specimens collected on different days. Healthcare providers should specifically request Cyclospora testing when the symptoms and exposure history raise concern. ommends using clear language during a medical appointment.

“Tell the clinician that you have persistent or recurring watery diarrhea during a known increase in cyclosporiasis cases,” he said. “Ask whether the stool test specifically includes Cyclospora. Do not assume every standard gastrointestinal panel looks for it.”

Patients should also tell their provider about recent travel, restaurant meals, packaged salads, leafy greens, fresh herbs and berries consumed during the two weeks before symptoms began.

Treatment Is Available, but It Requires Medical Supervision

The preferred treatment is the prescription antibiotic trimethoprim-sulfamethoxazole, commonly known as TMP-SMX and sold under brand names including Bactrim, Septra and Cotrim.

CDC clinical guidance lists a typical adult course as one double-strength tablet taken twice daily for seven to 10 days. Treatment may need to be longer for certain immunocompromised patients. ld not use this information to treat themselves. TMP-SMX can cause allergic reactions and may interact with medications used for blood pressure, blood thinning and other conditions. Pregnant patients, breastfeeding mothers, infants and people with kidney disease require individualized medical assessment.

There is currently no highly effective, well-established alternative for people who cannot tolerate sulfa drugs. CDC guidance notes that ciprofloxacin has shown only limited activity and may be ineffective in many otherwise healthy patients. o warned against delaying care while using unproven parasite-cleansing products.

“Online products containing wormwood, black walnut, oregano oil, garlic or other herbal ingredients have not been proven to cure human cyclosporiasis,” he said. “The greatest risk is not necessarily the supplement itself. It is the loss of time while diarrhea and dehydration continue.”

Patients should also speak with a physician before taking medications that slow intestinal movement. Such products may not be appropriate for every infectious cause of diarrhea and can mask worsening symptoms.

How to Reduce Your Risk

There is no vaccine against Cyclospora. Prevention depends primarily on safe food handling and reducing exposure to contaminated food and water.

The CDC recommends washing hands with soap and water before and after preparing fresh produce. Fruits and vegetables should be rinsed thoroughly under clean running water before being cut, cooked or eaten. Firm produce such as cucumbers and melons can be scrubbed with a clean produce brush, while bruised or damaged sections should be removed. educe contamination but may not remove every Cyclospora organism, particularly from produce with uneven or delicate surfaces. Consumers should never wash produce with soap, detergent or household bleach.

During the Michigan outbreak, state officials advised restaurants and commercial kitchens to consider whole heads of lettuce instead of prewashed bagged salad mixtures, remove the outer leaves and cook leafy greens when possible. They also recommended cooking fresh herbs, snow peas and other produce when practical. Heating food to at least 158 degrees Fahrenheit, or 70 degrees Celsius, kills Cyclospora. ces, knives, utensils and cutting boards should be cleaned after contact with unwashed produce. Cut or peeled fruits and vegetables should be refrigerated within two hours.

Travelers visiting areas where cyclosporiasis occurs regularly should avoid untreated water, ice made from unsafe water and raw produce that cannot be peeled or cooked. Routine chemical disinfection may not reliably kill the parasite. to Abandon Healthy Foods

Despite the outbreak, Dr. Armor said people should not stop eating fruits and vegetables altogether.

“The answer is not to become afraid of every salad or berry,” he said. “The answer is to remain informed, monitor official recall notices, wash produce carefully, cook higher-risk foods when practical and respond quickly if symptoms appear.”

The outbreak investigation remains active, and case numbers are expected to change as states review thousands of pending reports. The difference between federal and state totals reflects testing standards, reporting delays and the inclusion of probable cases rather than evidence that officials are hiding information.

For the public, the most important message is simple: persistent watery diarrhea is not something to ignore.

Anyone experiencing severe, prolonged or recurring symptoms should contact a healthcare provider, request appropriate testing and pay close attention to hydration. Early diagnosis can shorten the illness, reduce complications and help investigators identify the contaminated food source before more people become sick.

Parasite causing severe diarrhea spreads across th...