Massachusetts Stays Calm as Cyclospora Parasite Ravages the Midwest

A Nationwide Outbreak, But Not an Equal One

There have been 1,645 confirmed cases of cyclosporiasis acquired in the United States since May 1, and more than 5,100 additional cases are being investigated by the CDC — a sharp increase compared with recent years. But for Massachusetts residents watching this alarming story unfold, there is some reassuring news: the Bay State is not experiencing what the Midwest is going through — not even close.

While Midwestern states are currently dealing with an outbreak of the parasite, state officials say Massachusetts is not seeing a surge of reported cases. "There is no evidence currently that the outbreak of Cyclospora affecting multiple Midwestern states is affecting Massachusetts," a state Department of Public Health spokesperson said. Between May 1 and July 1, 18 cases of cyclosporiasis were reported in Massachusetts residents — "in line with the normal number of cases seen in Massachusetts during this time frame," the spokesperson said.

The Bay State is actually on track to finish with fewer cases of cyclosporiasis than in 2025 and 2024, when it saw 74 and 84 cases, respectively. Compare that to the Midwest, where the outbreak has been centered in Michigan, which has seen over 3,000 cases of the illness in the past few weeks. As of July 13, more than 400 people infected with Cyclospora have been reported to the CDC from four states in connection with a multistate outbreak: Michigan, Ohio, West Virginia, and Kentucky.

What Is Cyclospora — and Why Is It So Hard to Diagnose?

Spread through contaminated food or water and treatable with antibiotics, cyclospora can cause weeks of explosive diarrhea, cramping, nausea, and fatigue, according to the state's Department of Public Health. Its symptoms also include weight loss, bloating, vomiting, exhaustion, and fever. Some infected with cyclospora do not experience symptoms at all.

One of the most frustrating aspects of this parasite is how difficult it is to pin down. Unlike bacterial foodborne illnesses like salmonella, Shigella, and Campylobacter — which typically have an onset of one to five days after exposure — cyclospora takes about a week to two weeks to cause symptoms, making it even more challenging to figure out where it came from, according to Dr. Zoe Weiss, director of clinical microbiology at Tufts Medical Center. Cyclosporiasis "can be really challenging to distinguish, especially in the beginning, because a lot of foodborne illnesses can cause watery diarrhea," Weiss noted.

Patients may need to specifically request testing for Cyclospora, since routine stool tests don't always screen for this parasite. Not every lab or hospital may test for cyclospora right off the bat, given the parasite is relatively uncommon. That means case counts across the country are almost certainly an undercount of the true scope of the outbreak.

Lettuce and Fresh Produce Under the Microscope

As state and federal officials work to identify the source of the recent outbreak, Michigan health officials have identified lettuces or salad greens as one potential culprit. Past cyclospora outbreaks in the U.S. have been linked to fresh produce, including raspberries, basil, cilantro, scallions, snow peas, and bagged salads. Public health officials are interviewing people linked to the outbreak to find out what foods they ate before getting sick, but a specific food item has not yet been confirmed as the source.

The parasite spreads when people eat food — often fresh produce — that has come into contact with infected feces. It is not likely to spread from person to person. For now, the Massachusetts DPH advises washing fruits and vegetables with water and a brush to help remove cyclospora, though cooking produce will kill the parasite outright.

What Massachusetts Residents Should Watch For

Dr. Weiss says it is "reasonable to be vigilant" if you develop new, sudden-onset diarrhea and are not aware of having eaten anything unusual. Now that cases have appeared in places beyond the Midwest, healthcare providers need to be more aware of cyclospora as a possibility when evaluating patients with gastrointestinal symptoms. Cyclosporiasis is not usually life-threatening, but some people can become very ill and require hospitalization — so anyone with symptoms should contact their healthcare provider right away.

No deaths have been reported nationally, but the outbreak continues to grow. Kansas cases of the foodborne illness doubled in a single week to 55, as a national health agency reported cases exceeding 7,000