Michigan Nears 1,000 Cases of Diarrhea-Causing Parasite as Infections Spread Across Several States

A stubborn stomach illness that causes long-lasting diarrhea, cramps and bloating could be cyclosporiasis, a parasitic infection that often appears during warmer summer months.

Federal health officials say several states are now reporting more cases than expected for this time of year, raising concern about possible food or water-related clusters.

Health Officials Report Higher-Than-Expected Cases

The U.S. Centers for Disease Control and Prevention and the Food and Drug Administration are investigating several groups of cyclosporiasis cases across different states.

According to a CDC email obtained by CNN, clusters have been identified in Illinois, New York City, New York State, Pennsylvania and Texas.

Some of these cases appear linked to Mexican-style restaurants, a grocery chain and a catered event.

Possible Food Sources Under Investigation

The FDA’s Coordinated Outbreak Response and Evaluation network is conducting traceback investigations.

Investigators are looking at several possible food sources, including:

• White onions
• Green onions
• Cucumbers
• Cilantro

The CDC says there is currently no evidence proving that the earlier clusters are all part of one multi-state outbreak.

More Clusters Found in Other States

At least eight more cyclosporiasis clusters have also been found in Alabama, Kentucky, Michigan, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia.

However, many interviews with patients are still pending, and those investigations are in the early stages.

The CDC is expected to update its cyclosporiasis website later this week.

Michigan Appears to Have Largest Cluster

The largest cluster appears to be in Michigan.

The state usually records about 50 cyclosporiasis cases per year, but it has now reported nearly 1,000 cases since June 22.

That pattern suggests a possible outbreak from a common source.

According to Dr. Caitlin Rivers, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security, more than three dozen Michigan patients have been hospitalized.

Ohio and New York Also Report Increases

Ohio has reported 177 cyclosporiasis cases since the start of the year.

Of those, 171 were reported in June, mostly after June 20.

New York state, excluding New York City, has reported 112 cases this year, with 107 cases since May 1.

Health officials are still working to determine what is causing the increases.

Why Cyclospora Is Hard to Trace

Experts say cyclosporiasis outbreaks can be difficult to solve.

Dr. Jennifer McEntire, a microbiologist and founder of Food Safety Strategies, said much less is known about cyclospora compared with bacteria such as salmonella and E. coli.

She described the parasite as unusual and said it is causing serious problems this year.

Cyclospora Is Different From Other Foodborne Germs

Dr. Max Teplitski, chief science officer for the International Fresh Produce Association, said cyclospora is especially hard to trace to one source.

With bacteria such as E. coli or salmonella, scientists can sequence DNA and match illnesses to contaminated food or water.

A national surveillance system called PulseNet compares bacterial DNA fingerprints across cases in near real time.

When multiple cases match, investigators can often identify a common source.

Why DNA Matching Is More Complicated

Cyclospora does not work the same way as many bacteria.

McEntire compared bacterial DNA testing to reading a children’s book, while tracking cyclospora is more like reading “War and Peace.”

The parasite reproduces sexually and exchanges DNA, which means its offspring can look genetically different from one generation to the next.

That makes the family tree harder to follow.

CDC Uses Genotyping, but Interviews Still Matter

Over the past five years, CDC scientists have improved genotyping methods for cyclospora.

These tools can help group cases by strain-like patterns.

However, McEntire said the testing is still not as precise as it is for some bacterial foodborne illnesses.

Because of that, outbreak investigations still rely heavily on epidemiologists interviewing patients about what they ate and where they went.

Investigators may also check grocery receipts and credit card records to help fill memory gaps.

Experts Say Water Exposure Should Also Be Checked

Most questionnaires focus on food, but Teplitski said investigators should also ask about water exposure.

That includes swimming, lakes, water parks and well water.

He said several sources could spread the same parasite.

What Causes Cyclosporiasis?

Cyclosporiasis is caused by a single-celled parasite called Cyclospora cayetanensis.

It spreads through human feces.

People usually become infected by eating or drinking contaminated food or water.

Common sources include raw produce, swimming pools, lakes, splash pads and water parks.

Produce that is difficult to wash thoroughly, such as berries and fresh herbs, is often linked to outbreaks.

Foods Often Linked to Outbreaks

Since the mid-1990s, several foods have been frequently associated with cyclosporiasis outbreaks in the U.S. and other countries.

These include:

Food Item	Number of Outbreaks
Raspberries	12
Basil	11
Salad mixes, vegetable trays and coleslaw	8
Cilantro	6
Berry and fruit mixes	6
Lettuce	2
Snap peas	2

How the Parasite Infects the Body

People become infected after swallowing oocysts, the egg-like stage of the parasite.

Inside the intestines, the parasite develops into male and female forms, reproduces, and produces new oocysts.

Those oocysts can damage intestinal cells and later leave the body through stool.

In warm weather, the parasite matures outside the body for several weeks before becoming infectious again.

Because it needs time to mature outside the body, it usually does not spread directly from one person to another in the same household or workplace.

Symptoms of Cyclosporiasis

Dr. Rebecca Schein, an infectious disease expert at Michigan State University Health Care, said cyclospora symptoms can feel different from salmonella or E. coli infections.

Fever can happen, but it is not especially common.

The most common symptoms include:

• Very watery diarrhea
• Diarrhea more than three times a day
• Bloating
• Abdominal fullness
• Cramps
• General discomfort

Schein said the feeling can be like being overly full every day.

Symptoms Can Last for Weeks

Even people with normal immune systems may experience symptoms for several weeks.

Schein said the illness can take up to six weeks to go away on its own.

Symptoms may also come and go.

People with weakened immune systems may have symptoms that continue until they receive treatment.

How Cyclosporiasis Is Diagnosed

Cyclospora can be missed during routine stool testing.

Doctors often use multiplex stool tests to look for many pathogens at once, but cyclospora is usually not included on those panels.

To diagnose it, doctors must order a special test that uses a stain to make the parasite’s eggs appear bright pink or orange under a microscope.

The Texas Department of State Health Services warned in May that doctors may need to run up to three tests, spaced 24 hours apart, because the parasite’s eggs are not shed consistently.

Treatment for Cyclosporiasis

Once diagnosed, cyclosporiasis is usually treated with a combination antibiotic called trimethoprim-sulfa, sold under brand names such as Bactrim and Septra.

Treatment usually lasts seven to 10 days.

People with weakened immune systems may need a longer course.

Schein said the medication works because it interferes with the parasite’s ability to use folate to make energy.

When to Get Tested

Schein said people should seek testing if diarrhea lasts longer than three to five days.

Those living near a known outbreak should consider testing if symptoms last longer than two days.

She said treatment is recommended because cyclosporiasis can last a long time, cause significant discomfort and continue spreading into the environment if untreated.

Can Washing Produce Remove Cyclospora?

Researchers in Norway studied whether washing fruit can remove cyclospora.

In 2021, they contaminated blueberries and raspberries with cyclospora, cryptosporidium and giardia, then tested three washing methods.

The methods included:

• Rinsing berries under tap water for one minute
• Soaking and spinning berries in a salad spinner
• Washing berries in a vinegar-water mixture before rinsing and draining

Raspberries Are Harder to Clean

The study found blueberries were easier to clean because they have smooth surfaces.

Raspberries were harder to clean because they are bumpy and slightly fuzzy.

That may help explain why raspberries are often linked to outbreaks.

Cyclospora also appeared especially sticky and was harder to remove from raspberries than cryptosporidium or giardia.

Vinegar and Salad Spinner Methods Helped

The vinegar-water rinse removed more parasites from raspberries than plain water.

It was slightly more effective than the salad spinner method, but the difference was not large enough to be considered significant.

Both the vinegar and salad spinner methods removed most cyclospora eggs, but some remained on the fruit.

Researchers could not say whether the remaining amount would be enough to make someone sick.

FDA Tips for Cleaning Produce

The FDA recommends several steps to reduce contamination risks from fresh produce:

• Wash hands for 20 seconds with warm water and soap before and after preparing produce.
• Cut away damaged or bruised areas before eating or preparing produce.
• Rinse produce before peeling so dirt and bacteria do not transfer from the knife.
• Rub produce gently under plain running water.
• Do not use soap or produce wash.
• Use a clean vegetable brush for firm produce such as melons and cucumbers.
• Dry produce with a clean cloth or paper towel.
• Remove the outer leaves from lettuce or cabbage before use.

Cyclosporiasis is a difficult-to-trace parasitic illness that can cause weeks of watery diarrhea, bloating and cramps. With several states reporting higher-than-expected cases, health officials are investigating possible links to produce, restaurants, grocery chains, catered events and water exposure.

Because the infection can be missed by routine testing, anyone with persistent diarrhea should ask about specific cyclospora testing, especially in areas with known clusters.