Cyclosporiasis: What to Know About the Parasitic Infection

When diarrhea suddenly develops, many people try to pinpoint what they ate in the hours or days beforehand.

Cyclosporiasis doesn’t make that easy.

The foodborne illness, caused by the parasite Cyclospora cayetanensis, can take between two and 14 days to cause symptoms after a person consumes contaminated food or water.

“I can remember what I had for dinner last night,” says Scott Roberts, MD, a Yale Medicine infectious diseases specialist. “But it’s really hard for me to remember what I had for dinner two weeks ago.”

That delay is part of why cyclosporiasis outbreaks can be hard to trace. Cyclospora is often linked to contaminated fresh produce and has been responsible for outbreaks tied to foods such as leafy greens, herbs, and berries.

While many people recover fully, cyclosporiasis can cause days or even weeks of watery diarrhea and other digestive symptoms. Here’s what Dr. Roberts wants people to know.

Many gastrointestinal illnesses are caused by viruses or bacteria. Cyclospora is caused by a microscopic parasite.

The illness can cause watery diarrhea, stomach cramps, bloating, nausea, fatigue, and loss of appetite. Symptoms may be mild in some people, and some infected individuals may have no symptoms at all.

Unlike some other gastrointestinal illnesses, such as norovirus, cyclosporiasis is not thought to spread easily from person to person.

"The prevailing wisdom is that it’s not contagious," Dr. Roberts says. "When you excrete the parasite in the stool, it takes at least a week to mature to the point of being infectious."

Sharing a bathroom with someone who is infected is not considered a major risk, and families generally don’t need to worry about bleach-wiping every surface to prevent immediate spread, Dr. Roberts says. Instead, infections are typically linked to contaminated food or water.

Unlike illnesses that spread easily through close contact, cyclosporiasis is typically linked to food contamination that occurs before produce reaches consumers.

Washing fruits and vegetables can help reduce contamination, but it may not completely eliminate the risk, Dr. Roberts says. Removing the outer leaves of lettuce may also help.

According to guidance from the Centers for Disease Control and Prevention, cooking food to an internal temperature of 158°F is the most reliable way to kill the parasite. Because many foods linked to Cyclospora outbreaks are eaten raw, however, prevention can be challenging.

Dr. Roberts says consumers shouldn’t avoid fresh produce altogether. Large outbreaks are often associated with products distributed across multiple states, and the specific source of contamination is not always immediately known. For that reason, locally grown produce may carry less risk, Dr. Roberts says.

Furthermore, as with other foodborne illnesses, experts recommend washing hands with soap and water before preparing food and after using the bathroom.

Most Cyclospora infections improve on their own, but persistent diarrhea can make it difficult to stay hydrated.

“The biggest problem with this would be dehydration,“ Dr. Roberts says.

Older adults, young children, and people with weakened immune systems are at higher risk for complications, making it important to replace fluids and electrolytes.

Drinks containing electrolytes, such as oral rehydration solutions, Pedialyte, or sports drinks, may be more helpful than water alone because they replace salts and minerals lost through diarrhea. Eating regular foods, as tolerated, can help as well.

People should contact a healthcare provider if symptoms persist, worsen, or are accompanied by signs of dehydration, including dizziness, lightheadedness, a racing heart rate, or low blood pressure.

"If you’re seeing persistent diarrhea beyond three days, especially more than a week, that’s a concern and you should reach out to your primary care physician," Dr. Roberts says.

When diarrhea strikes, many people reach for over-the-counter medications such as Imodium (loperamide). But experts recommend thinking about what’s causing the symptoms before taking an anti-diarrheal medication.

Such medications, Dr. Roberts notes, are most helpful when diarrhea is caused by a noninfectious condition, such as medication side effects. Drugs like Imodium slow the movement of the intestines, which can reduce symptoms, but potentially keep a parasite, virus, or bacterium in the digestive tract longer.

For that reason, people who have diarrhea accompanied by a fever—which would be another sign of an infection—should consult with their healthcare provider before taking an over-the-counter medication, Dr. Roberts says.

Cyclospora can also be difficult to diagnose. Many routine stool tests don't look for parasites. Even when testing is performed, infections can sometimes be missed because the parasite isn't shed consistently in every stool sample.

More specialized molecular PCR tests can detect Cyclospora's genetic material, but those tests may not be readily available in every setting and often must be sent to outside laboratories, which can delay results, Dr. Roberts says.

Unlike many viral causes of diarrhea, however, cyclosporiasis can be treated with antibiotics when necessary. The preferred treatment is trimethoprim-sulfamethoxazole (Bactrim), although the medication isn't suitable for everyone because some people are allergic to sulfa drugs and alternative treatments may be less effective.

Most people won't need antibiotics. But Dr. Roberts says patients who are immunocompromised or have persistent, worsening, or relapsing symptoms should talk with their provider about testing and treatment.