More than a stomach bug, Cyclospora can cause weeks of severe illness

Cyclospora may not be as familiar as other foodborne illnesses like Salmonella or E. coli, but this intestinal parasite can cause weeks of debilitating diarrhea, fatigue, and stomach cramps, often after people unknowingly consume contaminated fresh produce or water. While most healthy adults recover with appropriate treatment, the infection can pose a greater risk for older adults, young children, and people with weakened immune systems.

Understanding how Cyclospora spreads, recognizing its symptoms, and knowing when to seek medical care are key to preventing complications. Although Cyclospora is relatively uncommon, it can linger for days or even weeks if left untreated, leaving patients dehydrated, exhausted, and unable to work or perform normal daily activities. Because the illness is caused by a parasite, not a virus or bacterium, recognizing symptoms early and seeking medical care can lead to faster treatment and recovery.  

Two experts from The University of Texas Medical Branch (UTMB Health), infectious disease specialist Miguel Cabada, MD, and emergency medicine physician Dietrich Jehle, MD, explain what you need to know about identifying, treating, and avoiding this often-overlooked foodborne illness.

Upset stomach vs Cyclospora

Everyone has experienced an upset stomach after overeating or eating something disagreeable. The next few hours may be unpleasant, but the digestive system generally restores itself fairly quickly.

“This is different from the usual stomach upset,” Cabada said. “Cyclospora is not a bacterium; it is a foodborne microscopic parasite that affects the lining of the small intestine. The parasite has a life cycle and a period of reproduction, so patients may develop diarrhea anywhere from two to 14 days after exposure.”

The parasite infects only humans and spreads when food or water becomes contaminated with human feces. After it is shed in stool, Cyclospora must mature in the environment for several days before it becomes infectious, making person-to-person transmission unlikely.

Fresh produce can become contaminated during growing, harvesting, or processing if it comes into contact with contaminated water or soil.

“As with any outbreak, hand-washing and general hygiene are the first defenses,” Cabada said.

Recognizing the symptoms

Because of the parasite’s life cycle, some patients experience recurrent episodes of acute diarrhea for several weeks or even longer, particularly older adults, young children, and people with weakened immune systems.

“If you have diarrhea that fails to improve after three to five days, it is unlikely to be food poisoning. It’s time to be tested for Cyclospora, especially if you have eaten produce that was imported from other countries,” he said. “In the week or two before becoming sick, think about where you have been and what you have eaten. It’s important to be careful about what you buy and where you buy it and to pay attention to recommendations and the sources of produce served in restaurants and sold in markets.”

He emphasized the need for patients with compromised immune systems to be proactive about testing if they fear exposure to Cyclospora.

Diagnosis and treatment

With any intestinal illness, Cabada said dehydration and weight loss are the greatest concerns and may require a trip to the emergency room. Fortunately, Jehle said simple laboratory tests can confirm the presence of the parasite, and antibiotics work quickly and effectively to relieve the misery of Cyclospora’s hallmark symptom: profuse, watery diarrhea that can last for weeks.

“We have a simple antibiotic, trimethoprim-sulfamethoxazole (Bactrim), that works very well,” Jehle said. “After just a week, more than 90% of patients will no longer have evidence of the parasite in their stools. Symptoms clear up, and if a patient does not tolerate a sulfa antibiotic well, there are alternatives.”

He said staying hydrated is essential and starting Bactrim while awaiting laboratory results may help shorten the course of the illness.

Prevention starts in the kitchen

But the best defense is to avoid consuming the parasite in the first place. Jehle recommends removing the outer layers of produce, particularly leafy greens, and rinsing them thoroughly before eating. However, because Cyclospora is resistant to chlorinated water, washing produce may not completely eliminate the parasite or risk of infection.

“It’s a tough bug,” he said. “If you cook produce to 150 degrees or deep-freeze it to minus 70 degrees, it will kill the organism. Don’t stop eating healthy foods. Just be careful and know where the produce is coming from.”

Cabada and Jehle stress that the risk of Cyclospora shouldn’t keep people from eating fresh fruits and vegetables, which remain an important part of a healthy diet. Instead, they encourage consumers to practice food safety by washing their hands before preparing or eating food, rinsing fresh produce under running water, and staying informed about food recalls and outbreak alerts.

While it’s not always possible to know exactly where produce was grown or whether it has been exposed to contamination, avoiding identified food sources and practicing good food hygiene can help reduce the risk of illness.