Updated July 15, 2026 at 6:17 AM CDT
A large number of cases of intestinal illness that causes diarrhea, nausea and fatigue have been detected in 34 states, according to federal health authorities, but the source is still under investigation.
As of Tuesday, the Centers for Disease Control and Prevention said it had received reports of 1,645 confirmed cases of cyclosporiasis, the gastrointestinal affliction caused by the parasite Cyclospora.
But the true number of infections is likely much higher, because that figure only represents cases reported by states directly to the CDC. There is also a lag between symptom onset and reporting, and many people recover from the illness without medical treatment. Michigan alone reported 3,309 cyclosporiasis cases as of Tuesday.
According to the CDC, as of Thursday, there have been 141 hospitalizations nationwide and no deaths.
Health officials are also investigating several clusters of cases that may be epidemiologically linked, including a multistate outbreak that includes at least four states: Michigan, Ohio, West Virginia and Kentucky.
People can contract the illness by eating food or drinking water contaminated with the parasite. Previous outbreaks have been linked to fresh produce. In 2018, McDonald's removed salads from restaurants in 14 states after federal health officials linked them to dozens of cases of cyclosporiasis, and tainted lettuce imported from Mexico was suspected to have sickened 400 people in the U.S. in 2013.
The illness does not spread from person to person, noted Gwen Biggerstaff, deputy director of CDC's Division of Foodborne, Waterborne, and Environmental Diseases at a press conference Tuesday: "The source of this outbreak is what we eat or drink — not casual contact with someone who's sick. "
It's typical for cyclosporiasis infections to rise in the spring and summer, but the CDC said Friday that multiple states had reported a larger jump in cases over the previous two weeks than they had during the same period last year. Only 249 cases had been reported nationally at this time last year.
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Where are cyclosporiasis infections occurring?
Health officials from California to Texas to Florida have reported cases of cyclosporiasis since the start of May.
Some of the hardest-hit areas appear to be in the Midwest and Northeast, including Michigan and New York.
The Ohio Department of Health reported 177 cyclosporiasis cases as of July 2, most of which occurred in June. Dr. Bruce Vanderhoff, director of the Ohio Department of Health, said cyclosporiasis is a "serious illness that can cause dehydration and require people to seek emergency medical care, and it should be taken seriously."
According to the CDC, those sickened with the disease have ranged in age from 5 to 88 years old.
The total number of nationwide cases is expected to grow, due to the estimated six-week gap between when illnesses begin and when they are reported to federal health authorities.
What's causing the outbreak?
That is still unclear. The CDC says it is continuing to try to identify the source or sources of the recent surge of cyclosporiasis infections.
Investigators do that in part by interviewing those who've become sick to find out what they've eaten. But since symptoms can appear anywhere between two days and two weeks or more after a person was infected, they may not remember everything they ate during that period.
Previous U.S. outbreaks of cyclosporiasis have been associated with raspberries, basil, cilantro, snow peas and lettuce, according to the Food and Drug Administration.
Federal health officials are urging doctors to test for the condition and to specifically request laboratory testing on stool samples.
How to prevent cyclosporiasis
Cooking produce is an effective way to avoid an infection, as heating food to 158 degrees Fahrenheit or higher kills Cyclospora.
Public health officials advise thoroughly rinsing all fresh produce under running water, even items that say they are prewashed. Do this before eating (if eaten raw) or cooking.
It is also important for home cooks to observe standard food safety rules, and that includes washing your hands with soap and water before and after handling fresh produce.
Public health officials don't yet know what foods may be the sources of the recent cases and stress the importance of washing any fresh produce you intend to eat.
What to do if you have symptoms
The CDC encourages people to seek medical attention if they have symptoms of cyclosporiasis, especially if you develop prolonged watery diarrhea along with fatigue or loss of appetite.
Dr. Kawsar Talaat, a physician at Johns Hopkins Hospital board certified in pediatrics, internal medicine and infectious diseases, says that cyclosporiasis can present in different ways. "If your diarrhea persists for more than a couple days, go see your doctor," Talaat says.
Some patients might experience a waxing and waning pattern. "If the diarrhea goes away and comes back, that's another sign of a potential Cyclospora infection," she says. "And again, go see your doctor."
Talaat says there is also an epidemiological importance to reporting. She says getting tested could help officials understand where the outbreak is coming from and how it's being transmitted.
Talaat also explains that standard tests for diarrhea can't diagnose cyclosporiasis. She echoes the CDC recommendation that clinicians need to request a test specifically for cyclosporiasis if suspected. It's a stool test, Talaat explains, but it can miss Cyclospora if the sample is small or taken at the wrong moment in the life cycle of the organism. You may have to send in more than one stool sample to confirm you have the parasite she says.
For those with cyclosporiasis, Talaat says there is an effective treatment: The antibiotic trimethoprim/sulfamethoxazole, brand name Bactrim or Septra, taken for seven to 10 days. While Cyclospora is a parasite, not bacteria, the antibiotic is effective against it.
Talaat says many won't even realize they had cyclosporiasis. "For most healthy adults, it's often a self-limited infection; it will go away by itself," she says.
But for those who are older, younger or immunocompromised, Talaat says to be proactive in getting tested and treated earlier to avoid risk of hospitalization.
NPR's Carmel Wroth contributed to this report.
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