UCLA Fielding's Dr. Anne Rimoin answers questions about Cyclospora and food-borne illnesses

Dr. Anne Rimoin, professor in the Department of Epidemiology and Gordon–Levin Endowed Chair in Infectious Diseases, answers questions about Cyclospora and food-borne illnesses.

Q: "What is Cyclospora, and what makes this outbreak so unusual?"

Rimoin: "Cyclospora is a tiny parasite that takes up residence in the small intestine. When someone ingests it through contaminated food or water, it can cause an intestinal illness known as cyclosporiasis. In the United States, outbreaks are often associated with fresh produce that is eaten raw.

This is a pathogen we know well. We see Cyclospora cases every year, particularly in the spring and summer. What stands out this year is the number of cases being reported, especially in Michigan and several neighboring states.

Cyclospora has an unusual life cycle. An infected person passes the parasite in stool, but it is not infectious immediately. It needs time in the environment to mature. During that period, it can get into water, fields, produce, or equipment used during growing, washing, packing, or processing. Someone else then becomes infected by eating contaminated food or drinking contaminated water. 

The cycle is people, environment, food, and then back to people.

Because Cyclospora needs time in the environment, it does not usually move directly through a household the way norovirus does. The contamination is more likely to have happened somewhere along the food-production chain, often well before the food reaches a grocery store, restaurant, or home kitchen.

We still do not know whether one food, one supplier, or one contamination event explains all the cases we are seeing. A large event can develop when a commonly eaten raw ingredient is distributed widely, when people continue to be exposed before the source is identified, or when several outbreaks happen at the same time.

A widely distributed raw ingredient can turn one sanitation failure into thousands of illnesses before anyone realizes the cases are connected."

Q: "How do people become infected?"

Rimoin: "Infection happens when someone eats food or drinks water carrying the parasite. In the United States, fresh produce is often involved because it may be eaten raw, with no cooking step to kill Cyclospora.

The contamination begins with human fecal material. It can enter irrigation water, water used to wash or cool produce, fields, packing facilities, or processing systems. Produce can then carry the parasite through the supply chain and eventually to the consumer.

This can happen far from where the illness is eventually diagnosed. Food may be grown in one place, processed in another, distributed across several states, and served under many different brand names or in many different restaurants.

By the time someone becomes sick, the contamination may have happened days or weeks earlier and hundreds or thousands of miles away."

Q: "What are the symptoms?"

Rimoin: "The symptom that really points toward Cyclospora is frequent, watery diarrhea. People may also have abdominal cramping, bloating, gas, nausea, loss of appetite, weight loss, and significant fatigue. Some people experience vomiting or a low-grade fever.

Symptoms usually begin about a week after exposure, although they can appear sooner or take up to two weeks or longer.

Cyclospora can last for weeks without treatment. Symptoms may start to improve and then return, sometimes more than once.

This often does not behave like a 24-hour stomach bug. The clue is watery diarrhea that continues or goes away and then comes back."

Q: "How are investigators trying to figure out what is happening?"

Rimoin: "Public health investigators start by identifying people who are sick and asking detailed questions about what they ate, where they shopped, which restaurants they visited, and whether they traveled.

They compare those interviews and look for foods, ingredients, stores, restaurants, or distributors that appear repeatedly.

Once a possible common exposure begins to emerge, investigators work backward through menus, receipts, distributors, processors, growers, and farms. They are trying to determine where the food came from, how it moved through the system, and where contamination may have occurred.

Every part of the public health system matters here. Clinicians must recognize the illness. Laboratories must test for it. Cases must be reported. Health departments must interview patients quickly. Investigators in different states must compare what they are seeing.

Outbreak investigations are epidemiologic detective work. One case rarely tells you very much. The pattern becomes visible when enough cases are diagnosed, reported, and connected."

Q: "Why is it so difficult to identify the contaminated food?"

Rimoin: "Most people do not become sick until about a week after eating the contaminated food. By the time investigators interview them, they are being asked to remember everything they ate over many days.

That is hard for anyone. The contaminated ingredient may have been lettuce in a sandwich, herbs in a sauce, greens in a restaurant meal, or one small part of a mixed salad. People may not know every ingredient they ate. The packaging may already be gone, and there may be no leftovers to test.

Fresh produce also moves through a very complicated distribution system. Products from different farms may be combined, processed, repackaged, and sold under multiple names. The same ingredient may end up in grocery stores, restaurants, schools, hospitals, and prepared foods across several states.

There may also be more than one outbreak occurring at the same time. We cannot assume that one food, one farm, or one processor explains every case.

The delay between exposure and illness gives contaminated food time to move widely before anyone knows there is a problem."

Q: "How can people protect themselves?"

Rimoin: "People can reduce their risk, although a consumer cannot eliminate the risk if produce was contaminated earlier in the supply chain.

Washing fruits and vegetables is still worthwhile. It can remove some of the parasite and reduce the amount of contamination present. It cannot guarantee that contaminated produce is safe.

Cyclospora is a little like microscopic glitter. It can get into the folds and crevices of a raspberry, leafy green, or bundle of herbs. You may wash some of it away, but you cannot be sure you removed all of it.

A laboratory study showed why the type of produce matters. A one-minute rinse removed most of the Cyclospora from smooth blueberries but removed far less from raspberries. More vigorous washing helped, but no method guaranteed complete removal.

Cyclospora comes off a smooth surface much more easily than it comes out of the folds of a raspberry or leafy green.

Cooking is the most reliable way to kill the parasite. People who want to lower their risk can choose cooked vegetables, fruits that can be peeled, and whole produce that can be washed thoroughly. Avoiding bagged salads, salad kits, and prepared leafy greens while the investigation continues is also a reasonable choice, especially for people who are older, immunocompromised, or medically vulnerable.

Washing helps. It does not solve contamination that happened earlier in the food-production process."

Q: "Are we seeing the same increase in California?"

Rimoin: "Cyclospora cases occur in California every year. As an epidemiologist, I am looking at whether we are seeing more cases than we would normally expect at this time of year.

So far, California is not showing the dramatic increase being reported in Michigan and several neighboring states. That is reassuring.

Seeing individual cases in California does not necessarily mean there is a California-centered outbreak or that the exposure happened here. Some people may have traveled or been exposed to food distributed in another region.

The large increase in Michigan and nearby states may reflect a widely distributed food exposure concentrated in that part of the country, several related clusters, increased testing, or some combination of those factors. The investigation is still underway.

For Californians, the message is to be aware and pay attention to updates. At this point, we are not seeing Cyclospora above the expected baseline in California."

Q: "When should someone seek medical care and ask about testing?"

Rimoin: "Anyone with persistent or recurring watery diarrhea should contact a healthcare provider, particularly if the illness lasts more than a few days, improves and then returns, or is causing dehydration, weakness, or weight loss.

People should seek care sooner if they are older, immunocompromised, pregnant, medically fragile, or having difficulty keeping up with fluids.

It is important to mention Cyclospora specifically. The parasite is not always included in routine stool testing, so it can be missed unless the clinician considers it and orders the appropriate test.

Cyclospora can be treated with trimethoprim-sulfamethoxazole, usually called TMP-SMX or Bactrim.

If watery diarrhea lasts more than a few days, or goes away and then comes back, do not assume it is an ordinary stomach bug. Call your clinician and ask whether Cyclospora testing is appropriate."

Q: "What does this outbreak tell us about the food supply and public health surveillance?"

Rimoin: "This outbreak shows how much food safety depends on what happens before food ever reaches a consumer’s kitchen.

Fresh produce passes through many steps. It is grown, irrigated, harvested, washed, packed, processed, transported, and distributed. A sanitation or water failure at any point can expose people across multiple states.

Consumers can take reasonable precautions, but they cannot fully protect themselves from a problem they cannot see and that may have occurred weeks earlier. The solution requires identifying the contaminated product, tracing it through the supply chain, and correcting the failure that allowed the contamination to happen.

This also shows why public health surveillance matters. We need clinicians who recognize the illness, laboratories that can test for it, health departments that can interview patients quickly, and agencies that can connect cases across jurisdictions.

We will never prevent every contamination event. We need a system that can recognize unusual illness quickly, identify the source, warn the public, and stop additional exposures.

Cyclospora may begin with one person having diarrhea, but identifying an outbreak requires the entire public health system to see the larger pattern."