A stomach illness that seems to get better and then suddenly returns may not be a typical stomach bug.
Cyclospora is a foodborne parasite that can cause weeks of watery diarrhea, fatigue, and digestive symptoms. In 2026, reported U.S. infections increased dramatically, prompting a CDC health advisory (1). Knowing how to recognize symptoms and when to seek testing can help families avoid prolonged illness.
In this article, you’ll learn what Cyclospora is, how to recognize cyclosporiasis symptoms, what the current outbreak means for families, when supportive home care may be enough, when medication is recommended, and what pregnant people, babies, children, and breastfeeding families need to know.
Cyclospora Quick Facts
- Causes watery diarrhea that may come and go for weeks.
- Most infections are linked to contaminated food or water.
- Symptoms often begin about a week after exposure.
- Many healthy people recover without medication.
- TMP-SMX is the CDC’s preferred treatment.
- Persistent symptoms should be evaluated because specific testing may be required.
What Is Cyclospora?
Cyclospora cayetanensis is a microscopic, single-celled parasite that infects the small intestine. The illness it causes is called cyclosporiasis.
People become infected after consuming food or water contaminated with the parasite. In the United States, outbreaks have frequently been connected to fresh produce, including leafy greens, herbs, berries, peas, and other fruits and vegetables commonly eaten raw (2).
Unlike many stomach bugs, Cyclospora does not usually spread directly from person to person.
After leaving an infected person’s body through stool, the parasite must spend time in the environment before it becomes infectious. This means a child is unlikely to catch Cyclospora directly from a sibling in the way that norovirus or Giardia can spread through a household (2).
To learn more, read this article: Food Poisoning: Symptoms, Remedies, and When To Call a Doctor
What Is Happening With Cyclospora in 2026?
The CDC considers May 1 – August 31 the annual cyclosporiasis season as cases typically rise during the spring and summer.
As of July 13, 2026, 1,645 confirmed domestically acquired cases had been reported across 34 states, compared with 249 cases during the same period in 2025. At least 141 people had been hospitalized, and no deaths had been reported. Several outbreaks remain under investigation, including one linked to contaminated fresh produce (1).
The much larger number of cases reported in 2026 led the CDC to issue a national health advisory asking healthcare professionals to consider Cyclospora in patients with prolonged or relapsing watery diarrhea, even when they have not traveled internationally (1).
One multistate outbreak has been linked to shredded iceberg lettuce served at certain restaurant locations in Indiana, Kentucky, Michigan, Ohio, and West Virginia. The CDC advised people not to eat shredded iceberg lettuce from the affected locations while the investigation remains open (3).
This warning does not apply to all iceberg lettuce, every location in the restaurant chain, or all produce from Mexico. The CDC is also investigating additional cyclosporiasis outbreaks that are not believed to be connected to this specific lettuce investigation (1,3).
Because outbreak information can change as investigators receive new laboratory and supply-chain information, check current CDC and FDA notices before making food decisions based on an older headline.
Cyclosporiasis Symptoms
Symptoms usually begin about one week after exposure, although they can appear anywhere from two days to two weeks or longer after contaminated food or water is consumed (2).
The most common symptom is frequent watery diarrhea.
Other symptoms may include:
- Loss of appetite
- Weight loss
- Abdominal cramping
- Bloating and gas
- Nausea
- Fatigue
- Headache or body aches
- Low-grade fever
- Vomiting
Some people infected with Cyclospora do not develop noticeable symptoms (2).
When to Suspect Cyclospora
Talk with a healthcare provider about Cyclospora testing if you have:
- Watery diarrhea lasting longer than a week
- Symptoms that improve and then return
- Recent consumption of raw produce
- Negative stool test despite ongoing symptoms
- Exposure during a Cyclospora outbreak
Why Cyclospora Is Often Missed
Cyclospora is not routinely included in every stool test. A standard ova-and-parasite examination may miss it, and not all gastrointestinal PCR panels test for Cyclospora. Even an infected person may not release enough of the parasite in every stool sample for the laboratory to detect it.
Healthcare professionals may need to specifically request Cyclospora testing. Several stool samples collected on different days may also be necessary (4).
The Relapsing Pattern Typical of Cyclospora
One of the biggest clues that an illness could be cyclosporiasis is that symptoms may improve and then return.
A child may appear to recover, begin eating and playing normally again, and then develop watery diarrhea, bloating, poor appetite, or fatigue several days later.
Without treatment, illness may last from a few days to a month or longer. Symptoms can disappear and return one or more times. This relapsing pattern can make families assume that a child caught a second stomach virus when the original infection never fully resolved (2).
Cyclospora in Babies and Children
Babies and young children can become dehydrated more quickly than adults.
Contact your child’s healthcare provider for repeated watery diarrhea, especially when it is accompanied by:
- Fewer wet diapers or trips to the bathroom
- Dry lips or mouth
- Few or no tears
- Poor feeding
- Unusual sleepiness
- Difficulty waking
- Repeated vomiting
- Weight loss
- Symptoms that improve and return
Continue breastfeeding or formula unless your child’s healthcare provider gives different instructions. Do not replace breast milk or formula with plain water.
Trimethoprim-sulfamethoxazole, or TMP-SMX, is the preferred medication for Cyclospora, but it is generally not recommended for infants younger than two months. Any suspected or confirmed infection in a young infant requires individualized pediatric management (5).
You might like this article, too: Vomiting in Infants and Children: Potential Causes, Home Care Tips, & When To Call a Doctor
Cyclospora During Pregnancy and Breastfeeding
Frequent diarrhea, vomiting, poor food intake, and weight loss can lead to dehydration, which deserves prompt attention during pregnancy.
Contact your prenatal provider for:
- Persistent watery diarrhea
- Difficulty keeping fluids down
- Reduced urination
- Dizziness or significant weakness
- Noticeable weight loss
- Symptoms that improve and then return
Treatment decisions during pregnancy need to consider both the effects of prolonged illness and the potential risks of medication.
Trimethoprim can interfere with folate metabolism. TMP-SMX should therefore be used during pregnancy only when the expected benefit justifies the potential risk. The medication is generally avoided close to delivery because sulfonamides may increase the risk of severe jaundice in a newborn. A prenatal provider may also review folate intake when treatment is needed during early pregnancy (5).
TMP-SMX is generally considered compatible with breastfeeding a healthy, full-term baby after the newborn period.
Additional caution is needed when the nursing baby is:
- Premature
- Jaundiced
- Ill or medically stressed
- Diagnosed with G6PD deficiency
In these situations, the prescribing clinician and the baby’s pediatrician should determine whether the medication is appropriate (5).
Who Is More Likely to Develop Prolonged Illness from Cyclospora?
Most healthy adults and children recover from Cyclospora, but more serious or persistent illness is a greater concern in:
- Infants and very young children
- Older adults
- People with weakened immune systems
- Organ transplant recipients
- People receiving chemotherapy
- People taking immune-suppressing medication
- People living with advanced HIV
- Anyone who is already medically fragile or undernourished
People with weakened immune systems may experience more severe or relapsing illness and may require a longer course of treatment (1,5).
Can You Recover from Cyclosporiasis Without Medication?
Yes, most people with healthy immune systems can eventually recover from cyclosporiasis without prescription medication. Supportive home care does not directly kill the parasite, but the immune system may clear the infection over time. The tradeoff is that untreated illness can last for weeks and may repeatedly improve and return (2,5).
Supportive home care may be reasonable at the beginning of a mild illness when the person:
- Can drink and keep fluids down
- Is urinating normally
- Has no signs of dehydration
- Is alert and behaving normally
- Has no significant weight loss
- Is steadily improving
- Is not medically high risk or an infant
Supportive care may include fluids, oral rehydration solution, rest, continued breastfeeding or formula, and small, nourishing meals as tolerated.
You might like this article, too: Signs of Dehydration In Kids & Infants, Plus Dr. Green Mom’s Homemade Electrolyte Drink Recipe
When Is Medication Recommended for Cyclosporiasis?
The CDC recommends TMP-SMX (the prescription antibiotic combination trimethoprim-sulfamethoxazole) as the treatment of choice for symptomatic cyclosporiasis. It is commonly sold under brand names including Bactrim and Septra.
For otherwise healthy adults and children at least two months old, treatment generally lasts 7-10 days. People with weakened immune systems may need a longer course (5).
Medical evaluation becomes more important when diarrhea:
- Lasts more than a few days
- Improves and then returns
- Is frequent or severe
- Causes dehydration or weight loss
- Prevents normal eating or drinking
- Occurs after a known outbreak exposure
- Affects a baby or medically fragile child
- Occurs during pregnancy
- Affects someone with a weakened immune system
Supportive care replaces lost fluids and electrolytes and helps the body tolerate the illness. TMP-SMX acts against Cyclospora and can shorten or resolve a prolonged or relapsing infection.
Unfortunately, no supplement or probiotic has been shown in clinical research to eradicate Cyclospora (5).
You might like this article, too: How To Treat Viral Gastroenteritis (aka Stomach Flu) Naturally
What Are the Potential Downsides of TMP-SMX?
TMP-SMX can be effective, but like most medical interventions, it is not always risk-free.
The most common side effects include:
- Nausea
- Vomiting
- Reduced appetite
- Abdominal discomfort
- Diarrhea
- Rash or hives
Because some of these effects overlap with cyclosporiasis symptoms, tell the prescribing provider if diarrhea, nausea, or appetite loss becomes significantly worse after treatment begins (6).
Rare but serious reactions can include:
- Severe allergic reactions
- Blistering or peeling skin reactions
- Liver or kidney injury
- Abnormal blood-cell counts
- Changes in potassium or sodium levels
A spreading or painful rash, blistering, mouth sores, facial swelling, difficulty breathing, unusual bruising, jaundice, or significantly reduced urination requires prompt medical attention (6).
TMP-SMX can also interact with other medications and may require extra caution in people with kidney disease, liver disease, folate deficiency, blood disorders, or conditions that affect potassium levels.
The prescriber and pharmacist should receive a complete list of medications and supplements before treatment begins.
Like other antibiotics, TMP-SMX can affect the normal bacteria living in the intestinal tract. Antibiotic-associated diarrhea can occur, and severe or bloody diarrhea during or after treatment should be reported to a healthcare provider (6).
To learn more, read these articles:
What If Someone Has a Sulfa Allergy?
A sulfa allergy is an adverse immune response to medications containing sulfonamides (primarily antibiotics like Bactrim, Septra, or Eryzole). There is no equally effective, well-established alternative to TMP-SMX for Cyclospora.
Medications commonly used for other intestinal parasites, including metronidazole, tinidazole, albendazole, and azithromycin, have not been shown to work reliably against Cyclospora. Ciprofloxacin has demonstrated limited activity in a small study but is often ineffective in clinical practice (5).
Depending on the severity of illness and the type of previous reaction, a healthcare professional may consider:
- Observation with supportive care
- A less-established alternative
- Carefully supervised desensitization in selected patients
Can Washing Produce Remove Cyclospora?
Washing produce is important, but it cannot guarantee that Cyclospora has been removed.
The CDC recommends:
- Washing hands before and after preparing produce
- Rinsing fruits and vegetables thoroughly under running water
- Washing produce even when it is labeled pre-washed
- Scrubbing firm produce with a clean produce brush
- Removing bruised or damaged areas
- Refrigerating cut or peeled produce within two hours
Routine chemical disinfection and sanitizing solutions may not eliminate Cyclospora. Do not wash produce with dish soap, detergent, bleach, or household cleaning products (1,10).
During an active outbreak, families may choose cooked vegetables more often, particularly when feeding babies or caring for pregnant, older, immunocompromised, or medically fragile family members.
Organic produce is not automatically protected from foodborne contamination. Both organic and conventionally grown produce should be handled safely.
When to Call the Doctor
Contact a healthcare professional for:
- Watery diarrhea lasting more than a few days
- Symptoms that improve and then return
- Signs of dehydration
- Unintentional weight loss
- Difficulty keeping fluids down
- Significant abdominal pain
- Blood in the stool
- Persistent diarrhea during pregnancy
- Concerning diarrhea in a baby
- Prolonged symptoms in someone who is immunocompromised
- Illness after eating food named in an outbreak notice
Seek urgent medical care for:
- Confusion
- Fainting
- Extreme weakness
- Very little or no urine
- Difficulty waking
- Severe abdominal pain
- Baby who is not feeding or producing a normal number of wet diapers
Mention recent restaurant meals, travel, and fresh produce eaten during the two weeks before symptoms began. This information can help healthcare professionals select the appropriate tests and help public health agencies investigate outbreaks (1).
You might like this article, too: How to Treat Diarrhea in Infants and Kids
Summary
Cyclospora is a foodborne parasite that can cause prolonged or relapsing watery diarrhea. Because routine stool tests may not always include Cyclospora, specific testing may be needed when symptoms persist.
Many healthy people eventually recover from cyclosporiasis with supportive care, but untreated illness can last for weeks. When symptoms are prolonged, severe, or recurrent, TMP-SMX remains the CDC’s preferred treatment.
Most diarrhea is not caused by Cyclospora. However, when symptoms last longer than expected—especially during an outbreak or after eating fresh produce—asking about Cyclospora testing may help identify the cause and speed recovery.
Because outbreak information can change as investigators receive new laboratory and supply-chain information, check current CDC and FDA notices before making food decisions.
References
- Centers for Disease Control and Prevention. Domestically Acquired Cyclosporiasis Cases in Multiple U.S. States, 2026. Health Alert Network Health Advisory, CDCHAN-00531. July 14, 2026.
- Centers for Disease Control and Prevention. About Cyclosporiasis. Updated July 14, 2026.
- Centers for Disease Control and Prevention. Cyclospora Outbreak Linked to Shredded Iceberg Lettuce Served at Taco Bell in Five States. Updated July 16, 2026.
- Centers for Disease Control and Prevention. Clinical Guidance for Cyclosporiasis. March 4, 2024.
- Centers for Disease Control and Prevention. Clinical Care of Cyclosporiasis. February 27, 2024.
- U.S. National Library of Medicine. DailyMed: Sulfamethoxazole and Trimethoprim—Prescribing Information.
- Centers for Disease Control and Prevention. Patient Care for Giardia Infection. February 20, 2024.
- Centers for Disease Control and Prevention. Treating Crypto. June 4, 2025.
- Centers for Disease Control and Prevention. Clinical Overview of Pinworm Infection. February 20, 2024.
- Centers for Disease Control and Prevention. Preventing Cyclosporiasis. Updated July 14, 2026.
