Got a nasty stomach bug that won’t go away? It could be cyclosporiasis, a parasitic infection that causes weeks of debilitating diarrhea, cramps and bloating.

This infection tends to occur during the warm summer months, but several states are reporting increases in cases beyond what they would normally expect at this point in the year.

Federal health officials say they are seeing a higher-than-expected number of cyclosporiasis cases spread across several states. They may not all stem from the same source.

The US Centers for Disease Control and Prevention and the Food and Drug Administration have been investigating several clusters of cases in Illinois, New York City, New York State, Pennsylvania and Texas, which appear to be linked to Mexican-style restaurants, a grocery chain, and a catered event, according to an email sent by the US Centers for Disease Control and Prevention to state and local partners that was obtained by CNN.

The FDA’s Coordinated Outbreak Response and Evaluation network is conducting traceback investigations on white and green onions, cucumbers and cilantro, in an effort to narrow down potential sources, the email said.

The CDC says there’s no evidence at this point suggesting these earlier clusters are part of a multi-state outbreak.

At least eight additional cyclosporiasis clusters have been identified in Alabama, Kentucky, Michigan, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. However, case interviews are still pending, and these investigations are still in their early stages, the CDC said. The agency plans to update cyclosporiasis website later this week.

The largest of these clusters appears to be in Michigan. The state says it typically logs about 50 cases of cyclosporiasis annually. It has now seen nearly 1,000 cases since June 22, pointing to an outbreak with a common source. More than three dozen of these patients have been hospitalized, according to Dr. Caitlin Rivers, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security.

Since the beginning of the year, Ohio says, it has received reports of 177 cyclosporiasis cases, with 171 of those coming in June, mostly since June 20. New York state says it’s seen 112 cases this year – outside of New York City – with 107 of those reported since May 1.

Investigations are underway to nail down the causes but may be slow going.

That’s because little is known about cyclospora compared with pathogens like salmonella and E. coli, said Dr. Jennifer McEntire, a microbiologist who is founder and CEO of Food Safety Strategies, which advises clients on dealing with cyclospora.

“It’s very peculiar, and obviously, like this year, it’s rearing its head in a very ugly way,” she said.

‘Cyclospora is a weird one’

Cyclosporiasis, which is caused by the parasite Cyclospora cayetanensis, is especially difficult to trace back to a single source, said Dr. Max Teplitski, who once led the Division of Food Safety at the US Department of Agriculture and is now chief science officer for the International Fresh Produce Association.

Teplitski recently co-chaired an advisory committee tasked by the US Food and Drug Administration with digging into why cyclospora outbreaks have steadily been increasing in the United States in recent years.

“Cyclospora is a weird one,” he said.

With some foodborne pathogens, like E. coli and salmonella bacteria, scientists can sequence, or read, their DNA to match a strain that’s making people sick with a strain that’s contaminating food or water. This gene matching is how scientists often spot outbreaks of foodborne illness in the first place.

A national network of surveillance labs called PulseNet constantly sequences the genes of bacteria that make people sick so they can compare the DNA fingerprints of cases in near-real time. When the fingerprints match across multiple cases in different states, scientists know to look for a common source.

But gene matching only works because the genetics of a particular strain of E. coli or salmonella change very little as they transmit from food to us or from person to person. The letters of their instructions read the same way each time, so they can be tracked pretty easily.

It doesn’t work quite the same way for cyclospora, McEntire said.

“For the bacterial pathogens, the technology is quite mature, and the organisms are really very, very simple. It’s like reading a children’s book versus reading “War and Peace” — cyclospora being the “War and Peace.” McEntire said.

“They’re all letters of the alphabet, but they are not the same thing,” she said.

Because these parasites have sex (more on that later) and swap pieces of their DNA to reproduce, their offspring share genes from their male and female parts, which means their genes look very different from one generation to the next, making the family tree harder to follow, Teplitski explained.

Over the past five years or so, McEntire said scientists at the CDC have “done an incredible amount of work” so they can now use genotyping to roughly bucket people and identify those who have one “strain” of cyclospora compared to another. But she says the fidelity with that testing is not the same as with investigations of other types of foodborne pathogens.

CDC scientists are using genotyping to help track cyclospora clusters. But solving an outbreak still largely depends on shoe-leather detective work done by epidemiologists who follow up with each person confirmed to have a cyclospora infection. They ask a detailed series of questions about what the sick person ate and when. Because people aren’t great at remembering everything they might have had for breakfast a week ago, they may also analyze data from grocery receipts and credit card purchases to help fill in the gaps. It’s painstaking work.

Typically, these questionnaires are focused on food. Teplitski says he hopes investigators are also looking at water sources like lakes and water parks.

“We certainly hope that they go back and they ask their patients, ‘What about recreational activities? What about other types of exposure to well water?’ ” he said. “All of these are multiple sources of the same parasites.”

What causes cyclosporiasis?

Cyclosporiasis is caused by a single-celled parasite spread through human feces. People get it by eating or drinking contaminated food or water, usually when swimming or when eating raw produce.

Produce that is hard to wash thoroughly, like berries and fresh herbs, is a common source, as are swimming pools, lakes, splash pads and water parks.

Foods most frequently associated with outbreaks in the US and other countries since the mid-1990s include:

• Raspberries: 12 outbreaks

• Basil: 11 outbreaks

• Salad mixes (including vegetable trays and coleslaw): 8 outbreaks

• Cilantro: 6 outbreaks

• Berry/fruit mixes: 6 outbreaks

• Lettuce: 2 outbreaks

• Snap peas: 2 outbreaks

Once someone swallows the oocytes, or the egg-like stage of the parasite, a plot worthy of an “Alien” movie plays out in the intestines.

First, they differentiate into male and female forms, have sex and reproduce. (Yes, all this happens in your gut.) Their oocysts, or eggs, then burrow into the intestinal wall, where they destroy cells and are shed back into the environment when we poop.

When the weather is warm, they grow and mature outside the body for several weeks before creating more spores that are ready to infect someone else.

Because the spores need time to mature outside the body, people don’t typically pass the parasite to other people they live or work with. Transmission tends to happen more indirectly.

What are the symptoms of cyclosporiasis?

The symptoms of a cyclospora infection “are a little different than you sometimes see with Salmonella or E. coli,” said Dr. Rebecca Schein, an infectious disease expert at Michigan State University Health Care.

Sometimes people run a fever, she said, but it’s not especially common.

“It’s just more very watery diarrhea. More than three times a day and then feeling kind of bloated, full, uncomfortable,” Schein said. “Sort of like you just ate Thanksgiving dinner, but every day.”

Even healthy people can see this stomach bug continue for weeks.

“If you have a normal immune system, it will eventually go away, but it could take six weeks,” Schein said. The symptoms may come and go, too.

People who have compromised immune systems could see their symptoms persist.

In those cases, “The symptoms will not go away until you treat it,” Schein said.

How is cyclosporiasis diagnosed?

Normally, when doctors are looking for the cause of a stomach bug, they will check a patient’s stool with a multiplex test, a single lab test that looks for multiple pathogens at the same time.

Cyclospora is not on those panels.

“It can be easily missed if you don’t do the right test, and that’s kind of the one of the hard parts about this,” Schein said. Doctors have to order a particular kind of test that requires a special stain that turns the eggs of the parasite bright pink or orange so they can be seen under a microscope.

The Texas Department of State Health Services posted a health advisory in May warning that because the eggs shed from the body inconsistently, doctors may need to do as many as three tests spaced 24 hours apart to make an accurate diagnosis.

How is cyclosporiasis treated?

Once the infection has been diagnosed, treatment is relatively straightforward, Schein said.

The parasite is treated with a combination of antibiotics called trimethoprim-sulfa, which is sold under the brand names Bactrim and Septra. A course typically runs seven to 10 days, though people with reduced immunity may need to take it for longer.

The reason an antibiotic works on a parasite, Schein said, is that it interferes with Cyclospora’s ability to use the vitamin folate to make energy. It works on some other types of parasites as well.

If you’ve had diarrhea that’s gone on for longer than three to five days – or longer than two days if you live in an area near a known outbreak – it’s important to get tested, Schein said.

“The recommendation is to treat people who have cyclosporiasis, because it can last so long, and it’s just uncomfortable, and it can … spread into the environment if we don’t treat it,” she said.

Can you get rid of cyclospora by washing your produce?

Researchers in Norway studied this question in 2021, contaminating blueberries and raspberries with three kinds of parasites: cyclospora, cryptosporidium and giardia. Then they washed the berries three ways.

The first method involved putting the berries in a strainer and running them under plain tap water for one minute. The second involved filling a salad spinner with water and immersing the berries for one minute while stirring them by hand before draining and spinning them for 10 seconds. Lastly, they mixed one part vinegar with three parts of water in a bowl big enough to cover the berries and stirred by hand for one minute before rinsing and draining.

They learned a few things. It was easier to clean the smooth blueberries compared with the bumpy and slightly fuzzy surface of the raspberries, a finding that helps explain why raspberries top the list of foods associated with outbreaks.

Another curious thing was that cyclospora seemed to be extra sticky. It was tougher to get its eggs off the raspberries than it was the Cryptosporidium and the Giardia.

Finally, the vinegar water rinse got more of the parasites off the raspberries than rinsing them under plain water. It was a little bit more effective than the salad spinner method, but it wasn’t enough to make a significant difference in the results.

The salad spinner and vinegar methods were equally good, getting most of the cyclospora eggs off, but even so, some were left on the fruit. However, it’s not clear whether the remnants would be enough to make anyone sick.

Bottom line: Washing your produce is always a good practice for whatever nasties could be hitching a ride into your kitchen.

The FDA offers tips about handling and cleaning fresh produce:

• Wash your hands for 20 seconds with warm water and soap before and after preparing fresh produce.

• If the produce is damaged or bruised before eating or handling, cut away the damaged or bruised areas before preparing or eating.

• Rinse produce before you peel it, so dirt and bacteria aren’t transferred from the knife onto the fruit or vegetable.

• Gently rub produce while holding under plain running water. There’s no need to use soap or a produce wash.

• Use a clean vegetable brush to scrub firm produce, such as melons and cucumbers.

• Dry produce with a clean cloth or paper towel to further reduce bacteria that may be present.

• Remove the outermost leaves of a head of lettuce or cabbage before using. (CNN)

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