(CNN) — Summer is the best time to be enjoying fresh berries and cool salads with a sprinkling of fresh basil, preferably poolside.
But this summer, with cases of diarrhea caused by a microscopic parasite called cyclospora climbing across several states, you may want to take extra care with how you prepare your produce and where you swim.
The epicenter of an outbreak is Michigan, where thousands of people have fallen ill, and nearby Ohio. Other states, including New York, Illinois, Indiana, North Carolina, and Texas have also reported a jump in cases, although it’s not clear whether they’re all part of the same outbreak.
The US Centers for Disease Control and Prevention says “multiple states” have reported an increase in cases in the last two weeks compared with the same period in 2025.
“CDC is aware that states are likely to report higher case counts of cyclosporiasis than reflected in CDC data and is working closely with states to update numbers as additional cases are confirmed,” it said Friday.
While it’s not likely to kill you, cyclosporiasis, by all accounts, is not something you want to deal with. The watery diarrhea, cramping and bloating it causes can quickly leave you dehydrated and even land you in the hospital.
“If you get norovirus or something, you might have a rough 24 or 48 hours, but people with this parasite can be sick for weeks or sometimes even months with a sort of relapsing pattern, and so that can really wear down your body,” said Dr. Caitlin Rivers, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security. She recently wrote about the outbreak in her “Force of Infection” newsletter.
Michigan health officials say lettuce or salad greens may be a potential source of the illnesses, but its investigation is continuing and other foods can’t be ruled out. No specific type, grower or supplier has been identified.
Based on past experience with this bug, there are some ways you can try to keep yourself safe.
Know how it infects people
The good news is that cyclosporiasis doesn’t pass directly from person to person. You get it by eating or drinking something that’s been contaminated several weeks prior, usually fresh produce or water from a swimming pool.
Michigan health officials say there’s “currently no evidence linking recreational water activities to this outbreak.” But this parasite is resistant to bleach, so it can show up in recreational water sources like chlorinated swimming pools and splash pads, but also in lakes and rivers. If you have an outbreak in your area, especially, it might be best to avoid public swimming areas.
Cook your fruits and veggies
When it comes to fresh fruits and vegetables, the safest thing to do to prevent getting sick is to cook them, Rivers said.
Cooking food to an internal temperature of 158 degrees Fahrenheit or higher kills cyclospora, according to the Michigan Department of Health and Human Services.
How long that takes will depend on your cooking method. Using a food thermometer can help you know that you’ve reached a safe temperature.
Always wash your produce
If it’s something you can’t really cook, like salad greens, you’ll want to wash it thoroughly — for at least a minute — by immersing it in water and swishing gently by hand. The bowl of a salad spinner is effective for this, for example.
Michigan health officials suggest purchasing whole head lettuce, rather than pre-washed, bagged lettuce or mixed salads, and discarding the outer layers of the leaves. You should still wash the inner leaves.
Researchers have also tested a rinse of one part vinegar to three parts water, and this also works to remove most cyclospora spores from produce.
In one study, even careful washing couldn’t remove all cyclospora, however, which proved to be stickier than other parasites.
“My read of this study is that rinsing helps, but it’s not reliable,” said Rivers.
Other practices that may help reduce the risk include breaking off and discarding the outer leaves of a head of lettuce, and scrubbing firm fruits and vegetables with a soft brush while rinsing.
Consider steering clear of certain high-risk foods
You don’t have to avoid all raw fruits and vegetables because of an outbreak with an undetermined cause. But you may want to skip foods that are harder to wash, or that people might be less diligent about washing, including.
Some of those harder-to-wash foods have been involved in outbreaks in the past:
- Raspberries
- Basil
- Salad mixes (including vegetable trays and coleslaw)
- Cilantro
- Berry/fruit mixes
- Lettuce
- Snow peas
What to do if you get sick
In the midst of a known outbreak, infectious disease experts recommend heading to the doctor for a diagnosis and treatment if you have diarrhea for longer than 48 hours.
“If it’s been more than 48 hours, it’s reasonable to test for it,” said Dr. Rebecca Schein, an infectious disease expert at Michigan State University Health Care.
Standard tests to look for stomach bugs don’t typically include cyclospora. Your doctor may need to special order it. Because the parasite sheds intermittently, you may also need several tests spaced 24 hours apart to get an accurate diagnosis.
Treatment is seven to 10 days of the combination antibiotic sulfamethoxazole-trimethoprim, which is sold as Bactrim or Septra.
“The recommendation is to treat people who have cyclosporiasis because it can last so long and it’s just uncomfortable,” Schein said. “And it can increase, you know, spread into the environment if we don’t treat it.”
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