EDITORS NOTE: EDS: SUBS throughout to update. NOTE: Story first moved Monday, July 13, at 7:23 p.m. ET.]

(Science Times)

This year is shaping up to be a bad one for the spread of cyclospora, a parasite transmitted through contaminated food and water that causes severe diarrhea.

At least 1,645 people across 34 states have been infected, the Centers for Disease Control and Prevention reported Tuesday. And 141 people have been hospitalized.

CDC officials said that they are also aware of more than 5,100 additional cases nationwide that they have not yet confirmed -- and these numbers are likely to grow.

“We anticipate continuing to see cases increase, possibly through the end of August,” Gwen Biggerstaff, the deputy director of the CDC’s Division of Foodborne, Waterborne and Environmental Diseases, said in a news conference Tuesday.

Michigan is currently reporting the most cyclospora infections in the country: 3,309 cases and 44 hospitalizations as of Tuesday morning, the highest number of cases ever reported in Michigan in a single year. The state typically records 40 to 50 cases per year.

This year is “on track to be the biggest year on record” for cyclosporiasis in the United States, said Caitlin Rivers, a public health researcher at the Johns Hopkins Bloomberg School of Public Health who is tracking the cases. Since 2016, the CDC has reported an average of about 2,800 cases of cyclosporiasis per year nationwide.

At least 400 cases in four states -- Michigan, Ohio, West Virginia and Kentucky -- appear to be linked to a common but unknown source, CDC officials said Tuesday.

On Monday, health officials in Michigan identified lettuce or salad greens as a potential source of the outbreak in that state, though they emphasized that the source was not definitive and others may be identified. Federal officials said Tuesday that they were investigating multiple types of produce -- including lettuce -- but have not yet found a specific source.

Some Taco Bell locations have removed certain ingredients -- including lettuce, cilantro, onion, pico de gallo and guacamole -- from their menus. In an emailed statement, the chain said that was “a precautionary measure” and that health officials have not confirmed a link between Taco Bell and the illnesses.

Cyclospora infections rarely cause serious complications and are not typically life-threatening, said Dr. Thomas Moore, an infectious disease specialist and clinical professor of medicine at the University of Kansas School of Medicine-Wichita. However, some people -- especially those in vulnerable groups -- may require hospitalization, such as for dehydration. It’s a good reminder to take food safety seriously, Moore said.

What is cyclospora? How is it transmitted?

Cyclospora is a microscopic parasite that infects people when they consume food or water that has been contaminated with human feces containing the oocysts (or eggs) of the parasite, said Keith R. Schneider, a professor of food safety at the University of Florida.

Cyclospora infections tend to rise from May through August in the United States. So it’s normal to see more of them this time of year, he said.

But the “huge spike” in cases, especially in Michigan, is clearly concerning, Schneider said. “Something is going on right now in that area.”

After ingesting the parasite, it can take from two days to two weeks or more for it to cause illness. The main symptom is watery diarrhea, with frequent, sometimes “explosive” bowel movements.

An infected person will then excrete the oocysts in their feces, but the parasite is not infectious in the feces until a week or two later. Because of this lag, the illness does not seem to spread directly from person to person, Schneider said.

And since it can take a while for symptoms to develop, it can be challenging to identify the source of an outbreak. The contaminated food or water would have been consumed long before someone became sick, Schneider said.

The current case counts are likely “the tip of the iceberg,” Moore said, with “many more coming down the road.”

How can you reduce your risk?

Past cyclospora outbreaks in the United States have mainly been linked to fresh produce, including raspberries, basil, cilantro, fruit mixes, snow peas, snap peas, lettuce and salad mixes. They have been caused by both imported and domestic fruits and vegetables and those prepared at home and in restaurants, said Donald Schaffner, chair of the food science department at Rutgers University.

Because the cause of the recent infections is uncertain, the best way to prevent illness is to follow standard hygiene and food safety practices, said Dr. Adam Ressler, an infectious disease physician with Michigan Medicine.

Always wash your hands with soap and water after using the bathroom and before preparing food, Moore said. Alcohol-based hand sanitizers do not kill cyclospora, he said, but soap and water does.

Rinsing fruits and vegetables with water is always a good practice, Moore said. Some cyclospora may still cling to contaminated produce after rinsing, but it will reduce their numbers and in turn can reduce your risk of getting sick or make the illness less severe, he said.

Cleaning produce with vinegar or other solutions is generally no more effective than doing so with running water, Schaffner said.

Produce is safest when heated to 158 degrees or higher, which kills cyclospora, according to Michigan’s health department.

Given the early signs that lettuce may be implicated in the Michigan outbreak, health officials there have recommended using whole heads of lettuce rather than bagged lettuce or premixed salad kits. Discard the outer two to three layers of leaves and then wash the inner leaves thoroughly under running water.

The department has also issued advice for other types of produce that have been implicated in previous outbreaks:

-- Cilantro and basil should be washed thoroughly under running water, while separating the leaves.

-- For scallions, trim the root end and remove the outer layer, and wash thoroughly under running water.

-- Snow peas should be washed under running water while rubbing the surface.

-- Raspberries are difficult to clean because their bumpy surface provides crevices where the parasite can hide. Consider cooking them in pies or jam. Freezing berries may reduce the number of parasites, though probably not entirely.

You can’t eliminate your risk completely, Schneider said. “There is an inherent risk with any raw food that you eat.”

What should you do if you have symptoms?

The symptoms of cyclospora infection -- including diarrhea, nausea, malaise, cramping and bloating -- look like those of a typical stomach bug, Moore said.

Because of that, many cases “fly under the radar,” he added. People may ride the illness out at home rather than see a doctor, and doctors may not always test for cyclospora. In most cases, people will recover from the illness on their own, with symptoms resolving within about a week or so, Moore said.

Staying hydrated is key, he said, so drink plenty of fluids. He recommended making a simple rehydration solution, with water, sugar and salt, for example, to replace electrolytes and fluids.

If your symptoms are severe or if they linger for more than a few days -- especially if you live in an area with a lot of cases -- it’s worth seeing a healthcare provider and getting tested for cyclospora, Ressler said.

Children, older adults and people who are pregnant or otherwise immunocompromised are at risk of more severe illness and should also seek treatment, Moore said.

If you test positive for cyclospora, a doctor can prescribe antibiotics that can reduce symptom severity and speed recovery, Ressler said. If left untreated, symptoms like chronic diarrhea can sometimes linger for months, he added.

Talk to a doctor before using over-the-counter antidiarrheal medications like Imodium or Pepto-Bismol, Ressler said. Depending on the type and severity of illness, these medications are not always recommended.

This article originally appeared in The New York Times.

Copyright 2026 The New York Times Company

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