Lettuce and leafy greens are the "potential source" of the cyclosporiasis outbreak that has sickened more than 3,000 people in Michigan, according to state health officials. Nationwide, nearly 7,000 people across 34 states have contracted the intestinal illness, which causes "explosive" diarrhea, with Michigan representing the largest cluster.

Cyclosporiasis is an intestinal, stomach-churning illness caused by a parasite called Cyclospora cayetanensis. People become infected by consuming contaminated food or water that contains the parasite. The symptoms of cyclosporiasis are similar to those of other food-borne illnesses like norovirus, E. coli or salmonella, except that cyclosporiasis "lasts longer and symptoms can get a little better and then they can come back," Dr. Jade Le, infectious diseases service line chief at Access TeleCare, told Yahoo.

The Centers for Disease Control and Prevention reported on Tuesday that 1,645 cases had been confirmed nationwide since May 1, with an additional 5,100 cases under investigation. "This is substantially higher than the 249 cases reported nationally by this same time last year," the federal public health agency said.

Michigan alone has confirmed at least 3,309 cases, according to the state's Department of Health and Human Services, with at least 44 people hospitalized. To put the scale in perspective, Michigan typically only records about 50 Cyclospora cases per year.

The CDC believes at least 400 cases across four states are connected, including Michigan, Ohio, West Virginia and Kentucky.

"Because cyclosporiasis is often underdiagnosed and underreported, the true number of illnesses is likely higher than what has been reported to CDC," the agency said. The median age of sick people is 44, ranging from 5 to 88, with 59% of cases in women. The median illness onset date is June 18, according to CDC surveillance data.

Health officials still have not identified a specific produce, grower or supplier tied to the outbreak. The working hypothesis is contaminated produce, but the parasite's slow incubation, roughly one to two weeks, makes it especially hard to trace back to a single meal or farm, The Washington Post reported.

Here's what else to know about cyclosporiasis.

How do people get sick with cyclosporiasis?

Preliminary results of the Michigan investigation have suggested that lettuce and leafy greens are the likely source of the state's cyclosporiasis outbreak. However, health officials noted that other sources have not been ruled out. It's also still unclear if cyclosporiasis cases in other states are part of the same outbreak or could be traced to other sources.

Taco Bell is reportedly under investigation for possible involvement in the Michigan outbreak, sources told the Washington Post. Signs notifying customers that the chain was "currently unable to sell Lettuce, Cilantro Onion, Pico de Gallo, and Guacamole due to a nationwide recall," were posted outside Detroit-area Taco Bells last week.

Past cyclosporiasis outbreaks have been linked to some types of imported fresh produce, such as raspberries, basil, snow peas, mesclun lettuce and cilantro, according to the CDC.

The initial source of the parasite, however, is unclean water, said Le.

Cyclospora spreads through feces. Produce on a farm could potentially become contaminated with feces if the water source that supplies that farm, such as a lake reservoir, is itself contaminated with feces or sewage, Le said. Farm produce could also become contaminated if a worker doesn't wash their hands after going to the bathroom and then handles the produce.

"What happens is we as humans ingest that contaminated food source, and we get this explosive watery diarrhea that can be accompanied by fever, belly cramps, nausea and vomiting," Le said.

She also stressed that cyclosporiasis is "not transmitted from person to person." You can't get the parasite by shaking the hand of someone infected with the parasite who didn't wash their hands after using the bathroom.

According to the CDC, it takes at least one to two weeks for cyclospora to become infectious after a person passes it in a bowel movement.

"You'd have to have maybe gone to the bathroom, not wash your hands, then started working in your garden around your lettuce, and a few days later, this parasite multiplies, infects that lettuce, someone ingests the unwashed infected lettuce and they get sick," Le explained.

Should I be worried?

"This diarrhea makes you feel terrible," Le said. "You should be worried if you live in a state where there's a current outbreak. But on a level of worry between one to 10, it's not the 10 or even a nine or eight. I would say just be more aware of the food you're eating."

The main concern with any diarrheal illness is severe dehydration, which can land people in the hospital, Le said. But, she added, "You're unlikely to die from this unless you've let those symptoms go on so long and did not seek medical care."

Do I need to throw out my produce to avoid getting sick?

You don't need to immediately throw out your fresh produce to prevent cyclosporiasis, Le said. But there are some steps you can take to make the ingredients in your fridge safer.

"Cooking is probably the most effective way to kill the parasite," Le explained. That can give you peace of mind when you're roasting root vegetables, but it doesn't mean you need to start boiling your fruits and salads. "Washing your vegetables and fruits well should get rid of most [parasites]," she said. And that still holds true for products labeled "prewashed," she said. For protection against cyclospora — and other food contaminants, such as E. Coli — these produce items should still be washed before preparing them, she recommends.

It also helps to know where your produce is coming from, Le said. "If you're going to a restaurant or you're going to an event where you're served these types of foods, there's not much you can do besides being aware, especially if you're in a state where there's an outbreak, keeping track of the news and waiting until the public health authorities identify the culprit," she explained.

The CDC and Cleveland Clinic also offer the following tips:

* Avoid consuming food or water that may be contaminated with feces. * Avoid drinking or cooking with untreated water. * Wash your hands with soap and water after using the bathroom and before, during and after food prep. * Along with washing and peeling vegetables before eating them, scrub produce with skin, such as melons and cucumbers, well. Cut away damaged or bruised areas on fruits and vegetables before preparing and eating them. * Follow food safety handling recommendations for safe preparation and storage.

Taking steps to reduce your risks of infection is important, but so is eating fresh produce. "I would not avoid eating any types of salads, herbs, fresh fruits and vegetables," Le said. "Continue to eat those products, but just be aware if you're in a state where there's been an outbreak," she cautioned.

What if I do get sick?

"Just being aware of your symptoms is the most important thing," Le said. "If you have watery, explosive diarrhea with stomach cramps, maybe a low-grade fever, reach out to your doctor sooner than later."

Your health care provider can diagnose cyclosporiasis by testing a stool sample, though patients may need to submit several samples collected on different days, as the parasite can be hard to detect even when symptomatic.

"You have to tell them, 'Can you please order a test that checks for cyclospora?' Some of the common stool tests may not specifically check for this parasite," Le also advised.

"If the symptoms are more than just a few days and are going on [for] a week or two, have a low threshold to ask your doctor to look for this."

For immunocompromised people, health care providers may prescribe antibiotics to treat cyclosporiasis. But for most patients, rest and plenty of fluids are the recommended treatment for diarrhea caused by the infection, according to the CDC. Le also noted that over-the-counter remedies may not help and discouraged using an antidiarrheal agent before being diagnosed by a doctor. In particular, she cautioned against using ivermectin, the drug widely misused to treat COVID-19, which is available over-the-counter at some pharmacies in Texas, where Le practices. The drug is a treatment for certain parasitic infections, but is not effective against cyclosporiasis, she said.