Updated July 10, 2026, 7:00 p.m. ET
- Infectious disease experts offer answers to important questions about cyclosporiasis as the number of cases in Michigan now grow at a pace of 20% to 30% per day.
- More than 1,500 people in Michigan have been infected since June 22 with the cyclospora parasite, which causes watery and sometimes explosive diarrhea.
- Doctors detail testing and treatment options as well as the best way to prevent getting cyclosporiasis amid the growing outbreak.
The number of people who’ve been infected with cyclosporiasis — a misery-inducing parasitic foodborne illness that causes watery and sometimes explosive diarrhea — is rising at a rate of 20% to 30% per day in Michigan, said Dr. Anurag Malani, an infectious disease specialist who also is the health care epidemiologist at Trinity Health Ann Arbor Hospital and vice chief of its medical staff.
Without a known source of the outbreak, there are no signs that its growth will slow anytime soon, said Malani, who also serves on the Board of Directors for the Infectious Diseases Society of America.
The 1,562 cases reported in Michigan between June 22, when the first cases of a massive outbreak were identified, and July 10, are likely an undercount, he said.
“There’s many more cases than what is actually reported,” Malani said. “Not everyone has the ability to get diagnostic testing … and there are people who can actually be asymptomatic as well. They may never know that they have it.”
With an incubation period that stretches from two days to two weeks after exposure and without knowing what the source of the outbreak might be, it is likely many more people will become infected in the coming days and weeks, he said.
The sickest people are showing up with cyclosporiasis in the hospital emergency departments, he said. Others are seeking treatment at urgent care centers and their primary care doctors’ offices.
“Most commonly, (they) have diarrhea that has not resolved after a couple of days,” Malani said. “Sometimes they have upper GI (gastrointestinal) symptoms. In the patients that get admitted (to the hospital), they often do have abdominal pain and significant nausea. … Sometimes they have clinical dehydration and electrolyte abnormalities, such as low potassium.”
As of July 10, at least 44 people in Michigan had been hospitalized for treatment of cyclosporiasis tied to the current outbreak, state health officials said.
What is cyclosporiasis?
Cyclosporiasis is an illness caused by a tiny, single-celled parasite called cyclospora cayetanensis, according to the U.S. Food and Drug Administration.
It is a protozoan parasite that is so small, it can only be seen with a microscope. It can infect humans when they eat food or drink water that has been contaminated with fecal matter.
The parasite generally does not spread directly from person to person because of its lifecycle, said Dr. Rebecca Schein, a pediatric infectious disease specialist at the University of Michigan Health-Sparrow in Lansing who also is an assistant professor of pediatric and human development in the College of Human Medicine at Michigan State University.
It can take days to weeks after being passed in an infected person’s poop to become infectious to another person when they ingest food or water that has been tainted by contaminated feces.
Although the cyclospora parasite isn’t endemic to Michigan, people have been infected when they travel to tropical and subtropical parts of the world and eat or drink contaminated food or water. It also can cause illness when tainted food is imported to the United States from endemic areas.
In summer months, there are some local cases every year, Schein said — estimating that in a typical year, about 50 people get sick with cyclosporiasis in Michigan.
Research from the University of Florida suggests that the incidence of cyclosporiasis infections is on the rise globally.
Joseph Eisenberg, a professor of global public health and epidemiologist at the University of Michigan’s School of Public Health, said it’s possible that climate change could be a driving factor.
“There is increasing concern that cyclospora will geographically expand due to climate change,” Eisenberg told the Detroit Free Press. “The parasite is largely found in subtropical areas. If it did become endemic in the U.S., it would likely happen in the South,” in such places as Florida and Louisiana.
How does Michigan’s outbreak compare to clusters in other states?
At least for now, Michigan appears to lead the nation in the number of cyclosporiasis cases. The state health department reported 1,562 people who’ve been sicked by the parasite as of July 10.
But it’s difficult to have a true sense of the scope of cases nationally because the U.S. Centers for Disease Control and Prevention’s surveillance data accounts for only about half that — 843 nationally in 31 states as of July 9.
The federal agency wrote: “Multiple jurisdictions have reported an increase of cases in the last two weeks compared to the same period in 2025. We assume a 6-week reporting lag between illness onset and case reporting to CDC; therefore, we anticipate that case counts will continue to rise as data are received.
“CDC teams are working diligently to collect, analyze, and provide data at the national level. State health departments may have more timely information about the situation in their jurisdictions. … Investigations to identify potential sources are ongoing.”
In neighboring Ohio, the Cincinnati Enquirer reported that the Ohio Department of Health has counted a total of 364 cases of cyclosporiasis statewide as of July 9. However, the Toledo-Lucas County Health Department reported it had 441 positive cases in its jurisdiction alone as of July 9 and also reported 661 people sickened with cyclosporiasis throughout northwestern Ohio.
The Michigan Department of Health and Human Services issued a county-by-county tally July 9, which shows the 10 most heavily affected Michigan counties are:
- 1. Monroe, with 215 cases.
- 2. Wayne, with 172 cases, with 12 being identified in the city of Detroit.
- 3. Washtenaw, with 159 cases.
- 4. Lenawee, with 155 cases.
- 5. Oakland, with 88 cases.
- 6. Shiawassee, with 82 cases.
- 7. Jackson, with 56 cases.
- 8. Ingham, with 55 cases.
- 9. Livingston, with 40 cases.
- 10. Genesee with 35 cases.
What caused previous cyclosporiasis outbreaks?
Local, state and federal health leaders say they are working to investigate the surge in cyclosporiasis cases in Michigan and across the United States but have yet to identify a common source of the infections.
In the past, outbreaks in the United States and Canada have been tied to bagged salad mixes and kits, such as precut lettuce blends with romaine, iceberg, red cabbage and carrots; fresh cilantro, basil, raspberries, snow peas and green onions.
Among them were outbreaks identified:
- In 1997, when more than 1,000 people in the United States and Canada were sickened by contaminated raspberries imported from Guatemala.
- In 2005, when people got sick after eating basil imported from Brazil, Peru, Mexico and Costa Rica.
- In 2018, when lettuce served at McDonald’s restaurants was the source of a multistate outbreak of cyclosporiasis infections.
- In 2019, when more than 2,400 people in 37 states and the District of Columbia became ill after eating imported basil from Mexico.
How to protect yourself from cyclosporiasis
The Michigan Department of Health and Human Services issued updated recommendations July 4 to help people reduce the risk of cyclosporiasis infection.
The safest option is to cook leafy greens, cilantro, basil, green onions, snow peas and raspberries after carefully washing them under clean, running water. Heating food to 158 degrees or higher kills the parasite.
If you must eat raw, fresh produce, the health department suggests:
- Washing hands with soap and water before and after handling or preparing food.
- Avoiding prewashed bagged lettuce or salad mixes. Instead, buy a whole head of lettuce. Throw away the outer two or three layers of leaves and thoroughly wash the inner leaves under running water.
- Thoroughly washing herbs, such as cilantro and basil, under running water. Separate the leaves as you wash them.
- Trimming the root end and removing the outer layer of green onions, which also are known as scallions. Once that’s done, wash them thoroughly under running water.
- Considering using frozen raspberries, rather than fresh, to reduce risk. The fruit’s bumpy surface makes raspberries especially difficult to clean. The parasite can hide in its tiny crevices. Freezing may reduce the risk, but the health department warns it does not guarantee the fruit won’t be contaminated.
- Rubbing the surface of snow peas while washing them under running water.
- Washing all fresh produce under clean running water, even if you plan to peel it. Scrub firm fruits and vegetables, such as melons and cucumbers, with a clean produce brush and cut away any damaged or bruised areas before preparing and eating.
- Refrigerating cut, peeled or cooked fruits and vegetables as soon as possible.
- Washing and sanitizing utensils and surfaces before and after handling food. Wash and sanitize display cases and refrigerators where fresh produce is stored along with cutting boards, surfaces and utensils used to prepare, serve or store fresh produce.
Will washing fruits and vegetables completely eliminate cyclospora?
No.
Although the washing and hygiene recommendations are good practice to prevent most foodborne illness, Eisenberg cautioned that cyclospora is a tough parasite to kill.
“Washing will not reliably remove all cyclospora, especially (on) fruits like raspberries, (which were) the cause of many cyclospora outbreaks in the past,” he said. “But it will reduce the concentration of contamination. That’s important because the dose ingested matters with respect to whether you will be infected and have symptoms. So, washing will reduce the risk of infection.”
The FDA warns on its website that cyclospora isn’t killed by commonly used disinfectants, including household bleach, either.
“Cyclospora is highly persistent in the environment,” Eisenberg said. “Heat is the only definitive way to kill the parasite, which is why cooking your food is recommended. … The best way to remove the parasite from surfaces and utensils is through hot water and soap and/or a dishwasher,” aiming for a water temperature above 158 degrees.
Symptoms of cyclosporiasis infection
According to MDHHS, symptoms of cyclosporiasis typically begin two to 14 days after exposure and may include:
- Diarrhea that is watery and can be explosive.
- Abdominal cramps and bloating.
- Loss of appetite.
- Weight loss.
- Fatigue.
- Nausea.
- Low-grade fever.
- Vomiting, although it is less common.
Anyone experiencing sudden gastrointestinal illness should be evaluated by a health care provider, state health officials say. Cyclosporiasis infections can be treated with antibiotics. However, if an infection remains untreated, the illness could last for days to a month or longer.
Is it safer to eat locally grown produce?
Without knowing the source of the current outbreak, Eisenberg said the decision to eat any fresh produce is about a person’s willingness to take risks.
“Michigan is experiencing a much higher burden of disease than other states,” he said. “Eating locally sourced foods will definitely decrease the risk of being infected with cyclospora, which is generally associated with imported produce.”
Still, he said, “we don’t yet know the cause of this current outbreak.”
It could be coming from a particular type of produce sold only to restaurants, for example, or only certain vegetables available at a group of supermarket chains.
The only thing that’s certain is that cooking fruits and vegetables to a temperature of at least 158 degrees is the safest bet, and thoroughly washing all produce is always a good practice.
Should everyone with cyclosporiasis be treated with antibiotics?
Even though most people who get cyclosporiasis have “a self-limited infection,” Schein said, “which means it will go away on its own eventually,” the public health recommendation at this time is to treat everyone with a confirmed case with antibiotics.
The illness can last four to six weeks and generally makes people feel terrible, Schein said.
“Because it lasts so long, the general recommendation is to be treated because you’ll feel better a lot sooner,” she said.
People with compromised immune systems, such as those who are on chemotherapy, transplant recipients and those who take medicine to suppress their immune systems, may be unable to rid themselves of the parasite without antibiotic treatment, Schein said.
Does it matter which type of antibiotic is used?
Yes. A particular type of antibiotic, called trimethoprim sulfamethoxazol, which is better known as Bactrim or Septra, has been shown to be most effective in treating cyclosporiasis.
However, if you’re someone who can’t take sulfa antibiotics — either because of an allergy or another underlying condition — Malani suggested talking with your physician about other options for treatment.
Can my pet get cyclosporiasis?
“No,” Malani said. “Humans are the only hosts.”
What should you do if you develop symptoms of cyclosporiasis?
If you become ill with gastrointestinal symptoms, such as sudden diarrhea, cramping and bloating that lasts more than a couple of days, contact a health care provider to seek testing.
Dr. Adam Ressler, a clinical assistant professor of infectious disease and internal medicine at the University of Michigan, said people who see a doctor with concerns about cyclosporiasis shouldn’t expect to leave that initial office visit with a prescription for antibiotics. Test results must come back first that show a positive result.
“Testing the stool is really important to confirm the diagnosis and make sure we know what we’re treating,” Ressler said.
Using antibiotics without knowing that there’s a cyclosporiasis infection can do more harm than good, Malani said, and can contribute to antibiotic resistance.
How long does it take to get a test result?
There are two testing options, and both use stool samples, Malani said.
One type is called an Ova and Parasite (O&P) test that involves collecting a stool sample, which is sent to a laboratory. There, the specimen is examined under a microscope to look for parasites and their eggs. It is generally inexpensive, costing about $20, Malani said, and typically takes three to five days to get a result.
The BIOFIRE Gastrointestinal molecular test costs about $475, Malani said, but it can identify 22 pathogens, including cyclospora, and usually returns results within a day.
He suggested checking with your insurance company to be sure the test will be covered, especially if your physician suggests the more expensive but faster option.
(This story has been updated with new information.)
Contact Kristen Shamus: kshamus@freepress.com. Subscribe to the Detroit Free Press.