Why Washing Your Produce Will Not Protect You From Cyclospora and What Actually Will

The cyclospora outbreak that has now surpassed 1,600 confirmed cases across the United States since May, with thousands more under investigation, is raising urgent questions that go well beyond the basics. Why does Michigan have more than 4,300 cases when its annual baseline is around 50? Why does washing produce not protect you? Why do patients feel better and then suddenly feel worse again? And what does recovery actually look like once the infection clears?

Adam Solomon, M.D., regional medical officer at CareMore Health, has answers, and some of them will surprise you. From the biology of why cyclospora behaves so differently from other gastrointestinal infections to the specific warning signs that mean it is time to stop managing symptoms at home and go to an emergency room, Solomon offers a level of clinical detail that goes far beyond what most people are reading about this outbreak right now.

The current outbreak has hit certain states like Michigan dramatically harder than others, with case counts running roughly 50 times above normal annual averages. What should people in heavily affected states be doing differently right now?

Adam Solomon, M.D.: There have already been over 1,600 confirmed cases of cyclosporiasis in the United States since May 1 and an additional 5,000-plus cases being investigated. Michigan alone has reported more than 4,300 cases compared to their baseline of around 50 per year. Of the confirmed cases, about 9% have required hospitalization, but fortunately, no deaths have been reported so far.

Given the volume of cases in Michigan, along with numerous cases in Ohio, West Virginia and Kentucky, there is most likely an epidemiologic linkage or common source. Given that the incubation period ranges from two days to two weeks or more, it can make tracing the source more difficult because reported cases need to recall what they ate for 2 weeks prior to getting sick.

What is most important for people to know is that cyclospora oocysts, the egglike form that this parasite produces, are resistant to typical chemical disinfection and sanitizing methods. This includes chlorine at concentrations used in standard produce washes, so people can’t just simply wash produce more carefully. They need to think about what they eat and how it is prepared.

Consider cooking produce rather than eating it raw, particularly leafy greens and fresh herbs, as heat kills the parasite. This is especially true of patients who are immunocompromised. The temperature needs to be over 165 degrees Fahrenheit (the standard food safety temperature) to destroy these oocysts. Freezing doesn’t work, and just microwaving is likely inadequate because microwaves heat unevenly.

People should also continue to monitor Centers for Disease Control and Prevention and state health department advisories so they’ll be aware once the source is identified.

If they develop watery diarrhea lasting 3 or more days, they should seek medical attention promptly. These oocysts aren’t seen in the standard stool specimen tests done as a workup for persistent diarrhea. Specific cyclospora testing must be requested and can require three specimens collected on subsequent days because of the intermittent nature of the infection.

On the positive side, person-to-person transmission is unlikely because oocysts require days to weeks in the external environment to sporulate and become infectious, so household contacts do not need isolation.

Cyclosporiasis is known for its relapsing pattern, where patients feel like they are recovering and then symptoms return. How do you explain that cycle to patients, and how does it change the way you approach treatment and follow-up care compared with a more straightforward gastrointestinal infection?

AS: This on-and-off course is a hallmark of cyclosporiasis that distinguishes it from most other types of infectious gastroenteritis. In people with a healthy immune system, diarrhea can persist for days to weeks or even over a month, with periods of apparent improvement followed by recurrence.

Cyclospora is a single-celled protozoan parasite, not a bacterium and not a virus. It has a complicated, multistep reproductive life cycle within the human intestine. After someone has swallowed an oocyst on contaminated produce or in contaminated water, the parasite makes its way to the small intestine, where it breaks open and releases tiny invaders called sporozoites. These burrow into the cells lining the intestinal wall. Those cells are normally responsible for absorbing water, nutrients and electrolytes.

Once inside these cells, the parasite begins reproducing asexually (essentially cloning itself) in a process called “merogony.” One single parasite can produce eight to 12 new parasites (called merozoites) inside one intestinal cell. As more and more grow in the cell, it will eventually get so full that it will burst, releasing all of those new parasites into the intestine. Those guys will then go on to invade a neighboring cell to do the same. This process will repeat over and over again. All of that damage to the lining cells eventually causes the villi (the tiny fingerlike projections in the intestine responsible for absorbing food and water) to shrink and flatten and the intestinal lining to become swollen and inflamed. Those changes cause the gut to temporarily lose its ability to properly absorb water and nutrients, leading to watery diarrhea, cramping and bloating.

The good news is that early treatment with a common, inexpensive antibiotic can shut all of this down within one to two days (although the full course is more like a week to ensure it is all cleared). People with a weakened immune system may need a longer course.

Vulnerable populations including older adults, immunocompromised individuals and people with underlying conditions face a much higher risk of serious complications from cyclosporiasis. What specific warning signs should caregivers and family members of high-risk individuals be watching for that would signal it is time to seek emergency care rather than manage symptoms at home?

AS: Patients with a weakened immune system can get quite sick quickly from an infection, so the threshold for seeking care needs to be lower. They should get seen as soon as symptoms start. The same goes for infants and very young children because they can be very susceptible to dehydration. On the other end of the spectrum, people who are 70 years of age or older should also have a lower threshold than most adults. Because other causes of diarrhea are still common, they can give it one to two days before an evaluation, but really shouldn’t wait longer than that.

Specific warning signs that suggest emergency care may be appropriate include signs of significant dehydration (decreased urination, dark urine, dry mouth, dizziness or lightheadedness upon standing, sunken eyes or confusion/lethargy), inability to keep fluids down (persistent vomiting), high or persistent fever (cyclosporiasis typically causes only low-grade fever; a high fever may suggest a complicating coinfection or an alternative diagnosis), bloody stool (cyclosporiasis can occasionally cause bloody diarrhea, but it isn’t expected and could suggest a different problem), symptoms of problems outside of the gastrointestinal system (this could be due to something else or an unusual but late complication of cyclospora infection weeks after the initial infection), or prolonged symptoms beyond three to five days without improvement (especially if there is significant weight loss or signs of malnutrition).

Once someone has been treated and recovered from cyclosporiasis, what does the path back to normal gut health actually look like, and are there dietary or probiotic strategies you recommend to help patients rebuild their gastrointestinal health after a prolonged bout of diarrhea and dehydration?

AS: The main damage here is to the cells that line the small intestine. Unlike the large intestine or colon, which is home to trillions of beneficial bacteria (called the gut microbiome), the small intestine is nearly bacteria-free. Recovery from cyclosporiasis is less about restoring bacterial balance and more about healing the physical damage to the small intestinal lining. There isn’t a lot of evidence to support the use of probiotics here or any kind of restrictive diet, so early refeeding with a normal diet is the way to go.

There is one caveat in that inflammation and damage to the intestine can cause a temporary deficiency in lactase, the enzyme that breaks down lactose, the main sugar in milk products. Therefore, it may be best to minimize or avoid dairy for a while just to be sure, though there are some data to suggest that yogurt may be better tolerated. I should note that this deficiency can occasionally last for weeks to months after the infection resolves.

It is important to ensure adequate hydration. Eating a normal diet and drinking water should be adequate to get people back to baseline, but if that is a challenge, oral rehydration solutions can be used. People shouldn’t turn to sports drinks because they tend to have too much sugar and too little sodium. If something is truly needed, Pedialyte is a good option (although marketed for children, it works fine for adults as well).

Washing produce is something most people think they are already doing correctly. What do most people get wrong about washing fresh herbs and vegetables that could still leave them vulnerable to cyclospora contamination, and is there a point at which washing simply is not enough?

AS: This is really important! Standard home washing of produce and even the commercial vegetable washes with chlorine or vinegar solutions won’t eliminate cyclospora oocysts. They are quite resistant to chemical disinfection. Most people simply and briefly rinse produce under running water or soak it for a few seconds. That may remove surface dirt and some bacteria but it is not going to kill cyclospora oocysts, which can adhere to irregular surfaces of leafy greens and herbs. Fresh herbs are especially risky because they are typically added to dishes uncooked, just before serving.

Given the current outbreak, the recommendation is to avoid eating raw produce altogether. Instead, cook it thoroughly, as heat is the most reliable method to kill the parasite.