Cyclospora is an uncommon but important cause of prolonged watery diarrhea in children, particularly during the summer months and during foodborne outbreaks. This episode reviews the epidemiology, clinical presentation, diagnostic pitfalls, treatment, and practical emergency department approach to recognizing and managing pediatric cyclosporiasis.

 

Learning Objectives

1. Recognize the clinical features and epidemiology of Cyclospora cayetanensis infection in children, including when to suspect the diagnosis in patients with prolonged watery diarrhea.
2. Select appropriate diagnostic testing for cyclosporiasis and identify the limitations of routine stool cultures, ova and parasite examinations, and gastrointestinal pathogen panels.
3. Apply evidence-based treatment and supportive care for pediatric cyclospora infection, including appropriate antimicrobial therapy, hydration, and follow-up considerations.

References

1. Stobbe M. Outbreak of diarrhea-causing parasite grows to more than 1,000 cases. ABC News. Published July 8, 2026. Accessed July 10, 2026.  
2. Bilung LM, Tahar AS, Yunos NE, et al. Detection of Cryptosporidium and Cyclospora oocysts from environmental water for drinking and recreational activities in Sarawak, Malaysia. Biomed Res Int. 2017;2017:4636420. doi:10.1155/2017/4636420.  
3. Giangaspero A, Gasser RB. Human cyclosporiasis. Lancet Infect Dis. 2019;19(7):e226-e236. doi:10.1016/S1473-3099(18)30789-8.  
4. Pyzocha N, Cuda A. Common intestinal parasites. Am Fam Physician. 2023;108(5):487-493.  
5. Centers for Disease Control and Prevention. Clinical care of cyclosporiasis. Updated March 8, 2024. Accessed July 10, 2026. 

Transcript

This transcript was generated using Descript and subsequently reviewed and lightly edited for spelling, grammar, and clarity. Minor inaccuracies may remain, and the audio recording should be considered the definitive version of this content.

 

Welcome to PEM Currents: The Pediatric Emergency Medicine Podcast. As always, I’m your host, Brad Sobolewski. It’s July and a seven-year-old comes into your emergency department with 10 days of watery diarrhea. They were seen earlier in the week and told it was probably viral gastroenteritis. Maybe they got a prescription for ondansetron, maybe they didn’t.

Stool cultures have already come back negative. Mom tells you, “Every time I think he’s finally getting better, the explosive diarrhea comes right back.” So what’s going on? Today we’re talking about Cyclospora. Honestly, it’s one of those organisms that most of us forget about until summer rolls around, or since medical school.

We don’t diagnose it every week, and depending on where you practice, you may go years without seeing a case. But then an outbreak happens, and maybe just a handful of sporadic cases show up, and suddenly you’re reminded that not every child with prolonged diarrhea has viral gastroenteritis. Cyclospora cayetanensis is a coccidian protozoan that’s transmitted through contaminated food or water.

In the United States, it’s most commonly associated with imported fresh produce, things like cilantro, basil, lettuce, salad mixes, and berries. Unlike bacterial food poisoning, everyone at the picnic usually isn’t sick, so it often presents as an isolated illness because the exposure happened days earlier and may have involved only one particular food item.

Families are often trying to remember the one thing that they ate that made everybody sick. Honestly, sometimes it’s simply the salad they bought at the grocery store a week ago. One thing that’s helped me remember these organisms over the years is that they each sort of develop their own personality.

You know, it’s often confused with Giardia and Cryptosporidium. So if the diarrhea is greasy, think Giardia. If it’s profuse, watery diarrhea after swimming, think Cryptosporidium. If it’s prolonged, watery diarrhea during the summer, think Cyclospora. Now, obviously there are exceptions, but I think that’s a pretty useful framework, especially when you’re seeing patients one after another in a busy ED.

One of my favorite pearls about Cyclospora, and I think it’s probably the one fact that’s most worth remembering because it explains how it sort of works. Unlike Giardia or Cryptosporidium, the oocysts that are passed in stool aren’t immediately infectious. They actually have to spend days to weeks out in the environment before they mature enough to infect somebody else.

So Cyclospora isn’t really spread by the kids sitting next to them at daycare. It’s spread by the salad they both ate last week. I think that’s a lot easier to remember than trying to memorize the organism’s life cycle. The incubation period averages about seven to 10 days, so by the time symptoms begin, families usually don’t remember exactly what their kid ate.

They’re certainly not connecting today’s diarrhea with the salad they had a week ago. The diarrhea itself is usually watery, sometimes pretty high volume, sometimes even explosive. One thing that’s a little deceptive is that it tends to wax and wane. Parents will tell you, “Yesterday I thought we had finally turned the corner,” and today they’re right back where they started.

Along with the diarrhea, you’ll often see abdominal cramping, bloating, nausea, fatigue, maybe even a low-grade fever, and if this has been going on for a while, some weight loss or poor weight gain. Most of these kids don’t walk in looking critically ill. They walk in because they’re still having diarrhea when everyone expected them to be over it.

That’s really the patient where Cyclospora should come to mind. And of course, not every child with prolonged diarrhea has it. Giardia is still incredibly common, especially after untreated water exposure, camping, or daycare. Again, those kids have greasy, foul-smelling stools with bloating and flatulence.

Cryptosporidium is the swimming pool organism. Those oocysts are remarkably resistant to chlorine, so swimming pools, splash pads, and water parks should all get your attention. Those patients usually have profuse watery diarrhea, but in otherwise healthy children, it tends to run its course over a couple weeks.

Cyclospora is different because it just hangs around. That’s really what makes me think about it. It’s not necessarily how sick the kid is, it’s that they’re still sick when they should actually be getting better. So aside from when you’re in the middle of an outbreak, when should you actually suspect it?

It’s really when a few things start lining up. The diarrhea has lasted more than a week. Maybe it got a little better and then came back. The kid has lost some weight or looks a little dehydrated. It’s summertime. The bacterial stool studies are negative. Maybe there’s a history of travel. Maybe there isn’t.

Maybe there’s a history of eating fresh produce. Maybe there isn’t. At some point, you have to stop saying, “Eh, it’s probably still viral,” and start asking yourself whether you’re dealing with something else. One teaching point that’s worth repeating, partly because it shows up on board exams and partly because it explains the epidemiology, is that Cyclospora isn’t spread directly from person to person.

Fresh stool isn’t immediately infectious because those oocysts still have to sporulate in the environment before they can infect the next person. So let’s say you’re thinking about Cyclospora. What do you actually order? A routine stool culture isn’t gonna help you. Even a routine ova and parasite examination may not be enough.

That’s an easy mistake to make because a lot of us were taught persistent diarrhea, send culture and O&P or a stool molecular pathogen panel. Many labs don’t specifically look for Cyclospora unless you ask them to or order it specifically. So there’s gastrointestinal PCRs for it, but you have to order them separately.

So you can actually get back a negative O&P and feel reassured when in reality no one’s really tested for Cyclospora. If your hospital has a multiplex GI PCR panel that includes it, that’s probably what you should order first. If you don’t, you probably have to order it separately. Another board pearl. So if you’re taking a board exam and they describe a child with prolonged watery diarrhea during the summer, maybe after eating fresh produce, and then they casually mention that the routine ova and parasite examination was negative, don’t let that throw you off.

That’s actually the clue. The organism may still be there, the lab just wasn’t sent to look for it. If your lab is using microscopy, Cyclospora can be identified with a modified acid-fast stain. The oocysts are a little larger than Cryptosporidium, and one interesting feature is that they stain variably.

Some stain bright red, while others hardly stain at all, giving them that classic ghost organism appearance, which I think is just, like, cool. And because oocyst shedding is intermittent, collecting two or three stool specimens over several days can improve the diagnostic yield if you still have a high index of suspicion.

The good news is that once you make the diagnosis, treatment is actually pretty straightforward. Trimethoprim-sulfamethoxazole remains the treatment of choice. In adult-sized patients, that means trimethoprim one hundred and sixty milligrams plus sulfamethoxazole eight hundred milligrams, just one double-strength tablet, orally twice a day for seven to ten days.

For kids greater than two months of age to eighteen years, it’s eight to ten milligrams per kilogram trimethoprim and forty to fifty milligrams per kilogram sulfamethoxazole per day orally in two divided doses for seven to ten days. Most children begin feeling noticeably better within twenty-four to forty-eight hours.

Honestly, this can be a pretty satisfying infection to treat because families have often been searching for an answer for a week or two. They’ve been told it’s viral. They’ve been waiting for it to improve, and then you finally make the diagnosis within a day or two of starting the right antimicrobial, the kid’s turning the corner. If the kid has a true sulfonamide allergy, things are a little more complicated, and I mean a true allergy, not just the parent who says, “Well, my mother was allergic to sulfa, so we’ve always avoided it.”

There really isn’t a perfect alternative. At this point, I’m probably talking to ID. Nitazoxanide’s been used, ciprofloxacin’s been used, but we generally try to avoid fluoroquinolones in children. Neither has been shown to work as well as trim-sulfa. And if you’ve got somebody who’s immunocompromised with Cyclospora, which fortunately I’ve never seen, I’d be calling ID.

Of course, don’t forget everything else that goes along with taking care of prolonged diarrhea. Oral rehydration is still the goal whenever possible. Some kids are gonna need IV fluids because by the time they get to you, they’ve been losing fluid for days. Replace electrolytes if they’ve been really sick.

And if the illness has dragged on for a couple of weeks, don’t forget the nutritional burden. Sometimes they’ve lost enough weight that getting them eating and drinking normally again becomes part of an ongoing treatment plan. The good news is that most otherwise healthy children recover completely.

Immunocompromised patients are the group that worries us the most. Their symptoms can become prolonged. They can relapse. Sometimes they require longer admissions or even secondary prophylaxis. One question that occasionally comes up is whether you need to repeat stool testing after treatment. In general, you don’t.

If the kid’s symptoms have resolved, then you don’t need to prove microbiologic cure. Treat the patient, not the PCR. If the kid feels better, you don’t need to prove that the pathogen is gone. So let’s get back to that hypothetical scenario we started with, that kid in July that’s had watery diarrhea for 10 days.

The stool culture was negative. They’re starting to lose weight. The parents are frustrated. Everyone keeps telling them it’s a virus. Maybe it is another virus. Maybe it’s two illnesses in a row. But this is the patient where you have to take a step back and consider just one more test instead of offering more reassurance.

That’s what Cyclospora is. Of course, you shouldn’t suspect it in every single child with prolonged diarrhea, but be aware of whether or not there’s an outbreak and test for it. Before wrapping this episode up, here’s a few more things I’d like you to remember. One, if watery diarrhea has lasted more than a week, especially during the summer months, make sure Cyclospora is somewhere on your differential.

Second, remember my comparison. Greasy diarrhea, think Giardia. Swimming pool exposure and profuse watery diarrhea, think Cryptosporidium. Prolonged watery diarrhea during the summer, think Cyclospora. Third, don’t let a negative routine ova and parasite examination or stool molecular pathogen panel falsely reassure you.

Make sure your laboratory is actually testing for Cyclospora, and remember that not every GI PCR panel includes it. Finally, once you make the diagnosis, treatment is pretty straightforward. Trimethoprim-sulfamethoxazole for most patients. Kids will start feeling better in 24 to 48 hours. Cyclospora isn’t the first diagnosis that comes to mind when a kid has diarrhea, and it shouldn’t be.

Viral gastro is still far more common. But when the diarrhea has been going on for 10 days, the stool studies are negative, the kid’s starting to lose weight, and the family says, “I thought we were finally getting better,” that’s when you have to stop and think about Cyclospora. It’s the child with the diarrhea that lingered.

If you enjoyed this episode, as the kids would say, like, rate, and review. Leaving that review on your favorite podcast platform really does help other people discover the show, and I’ve been fortunate to be teaching through this podcast since 2013 because of listeners like you. If you got ideas for future episodes or topics you’d like me to cover, I’d love to hear them.

For PEM Currents: The Pediatric Emergency Medicine Podcast, this has been Brad Sobolewski. See you next time.