New Parasite Warning: Cyclosporiasis Cases Spread to 18 States

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A fast-growing wave of infections from a microscopic stomach parasite is prompting new concern for U.S. travelers, as cyclosporiasis cases climb across at least 18 states and investigations widen just as peak summer vacation season gets underway.

Rapidly Expanding Parasite Outbreak Ahead of Peak Travel Season

Publicly available surveillance updates and recent news coverage indicate that cyclosporiasis, an intestinal illness caused by the parasite Cyclospora cayetanensis, has surged across a broad swath of the United States since early May. Initial federal summaries cited 145 domestically acquired cases in 17 states between May 1 and mid June, a figure now considered a clear undercount as state reports continue to rise and additional states confirm infections.

Michigan has emerged as the most prominent hotspot, with state health data showing an unprecedented spike in reported cases within a matter of weeks. By early July, nearly 1,000 infections had been logged in Michigan alone, making it the largest cyclosporiasis outbreak in that state’s history and one of the largest in the country in recent years. Neighboring counties in Ohio have reported several hundred additional illnesses, underscoring how easily the parasite can affect people who live, work or vacation across state borders.

Coverage from multiple outlets, including national wire services and regional health news organizations, describes a similar pattern in other states: higher than typical early summer case counts, ongoing cluster investigations and an absence of a single, nationwide source that would neatly explain the spread. Reports from Texas, Florida, Massachusetts and additional states show case numbers that exceed baseline expectations for this time of year, collectively pushing the tally across at least 18 states.

For travelers, the timing is significant. The steepest increases are being documented just as millions of people are on the move for holidays, road trips and large events, increasing the chances that infections acquired in one area will be detected far from the original point of exposure.

What Cyclosporiasis Is and How It Makes People Sick

Cyclosporiasis is a gastrointestinal illness triggered when people ingest food or water contaminated with the Cyclospora parasite. The organism is passed in human feces and must spend time in the environment before it becomes infectious, which means it does not typically spread directly from person to person like a common stomach virus. Past investigations have frequently linked outbreaks to fresh produce that is eaten raw, such as herbs, leafy greens or berries.

The illness is best known for causing prolonged, watery diarrhea that can become severe and debilitating, especially if untreated. Health guidance compiled by federal and state agencies notes that symptoms usually begin two to fourteen days after exposure and may include urgent diarrhea, stomach cramps, bloating, nausea, loss of appetite, weight loss and low grade fever. Some people describe the gastrointestinal symptoms as intense and recurring, with periods of improvement followed by a return of diarrhea.

Unlike many brief “stomach bugs,” cyclosporiasis can last for weeks if it is not correctly diagnosed and treated with specific antibiotics. Publicly available medical advisories emphasize that older adults, people with weakened immune systems, those undergoing cancer treatment and individuals with underlying health conditions may be at higher risk for more serious or prolonged illness. However, healthy adults and children can also experience significant disruption to daily life, work and travel plans.

Because the symptoms mirror more common digestive infections, many cases may never be tested or officially counted. Laboratory confirmation requires specialized testing for Cyclospora, which is not always included in standard stool panels unless clinicians request it or use multiplex tests that automatically check for a broad range of pathogens.

States Reporting Cases and Why Numbers Keep Rising

The precise number of affected states continues to evolve as new reports come in, but compilations from federal dashboards, state health alerts and national news coverage point to at least 18 states documenting infections acquired within the United States since May. These include states in the Midwest, South, Northeast and Plains, reflecting geographically scattered clusters rather than a single, easily mapped outbreak.

Michigan’s surge remains the clearest example of the outbreak’s scale, with case counts rising from a few dozen to several hundred in less than two weeks, and then approaching the 1,000 mark by early July. Local reports in Ohio describe more than 300 infections in a border county adjacent to Michigan, while Texas has confirmed several dozen cases that meet the federal outbreak case definition during the same time frame. Florida, Massachusetts and other states have reported their own increases, even when numbers are still within or slightly above expected seasonal ranges.

Experts cited in recent coverage note that official totals likely lag behind reality. Many people with milder symptoms never seek care, and even those who do may not receive the specific diagnostic tests needed to detect Cyclospora. Data published by federal health agencies also tend to stop at a cutoff date several weeks earlier than current news reports, creating a gap between surveillance summaries and what clinicians are seeing on the ground.

Despite the broad reach of the illness, public health updates consistently state that there is no evidence so far of a single, multistate source that connects every case. Instead, officials are examining multiple clusters and potential food exposures, suggesting that more than one contaminated product or supply chain could be involved, or that seasonal and environmental factors are driving a general increase in sporadic infections.

Travelers Urged to Treat Food and Water Choices Carefully

Although no formal nationwide advisory restricting travel has been issued, the pattern of infections is prompting renewed attention to food and water safety among people planning trips inside the United States. Cyclosporiasis has historically been associated with travel to tropical and subtropical regions, but in recent years, domestically acquired outbreaks linked to imported or U.S. distributed produce have become a recurring warm season concern.

Publicly available guidance from federal and state health agencies encourages travelers to be particularly cautious with fresh, uncooked fruits and vegetables. Thoroughly rinsing produce under running water, removing outer leaves from items like lettuce or cabbage, and avoiding dishes made with herbs or greens of uncertain origin are among the steps frequently recommended to reduce risk. Because the parasite is not easily killed by standard concentrations of chlorine, routine washing may lessen but not completely eliminate contamination.

Travelers are also advised to pay attention to safe drinking water practices, especially in areas where water quality may be variable or during activities such as camping, hiking or attending outdoor festivals. Using treated or bottled water for drinking and brushing teeth, and avoiding swallowing water from lakes, rivers or inadequately treated pools, can help prevent a range of gastrointestinal illnesses, including those caused by parasites.

Health information sites stress that good hand hygiene before eating or preparing food adds another layer of protection. While Cyclospora does not typically spread directly from one person to another, handwashing with soap and water can decrease the likelihood of ingesting the parasite after contact with contaminated surfaces or environments.

What To Do If You Get Sick During or After a Trip

With many cases connected to food and drink consumed days or weeks earlier, symptoms often appear during or after a trip, when people may dismiss them as ordinary traveler’s diarrhea. However, publicly available clinical guidance notes that diarrhea that persists beyond several days, especially when accompanied by fatigue, cramps and weight loss, should be evaluated by a health professional.

Medical resources recommend that anyone experiencing prolonged or severe gastrointestinal illness inform their clinician about recent travel, restaurant visits, catered events and foods eaten raw, such as salads, berries, herbs or prepackaged fresh meals. This information can help prompt testing for Cyclospora, which in turn allows for targeted treatment. A commonly used antibiotic combination can significantly shorten the duration of illness once the infection is confirmed.

People who develop symptoms such as lightheadedness, signs of dehydration, inability to keep liquids down or persistent diarrhea that disrupts normal activities are encouraged to seek care promptly. Guidance directed at older adults and those with weakened immune systems emphasizes the importance of not waiting for symptoms to resolve on their own, since cyclosporiasis can be more serious in these groups.

Health departments across several states are asking clinicians, through public alerts, to consider cyclosporiasis when evaluating patients with prolonged diarrhea during the summer months and to report confirmed cases. For travelers, the takeaway is that a stubborn “stomach flu” after a trip may in fact be part of a wider pattern of parasitic illness that is currently under investigation in at least 18 states.