Cyclosporiasis is a seasonal intestinal infection. Here’s what to know

Cyclosporiasis is a seasonal intestinal infection. Here's what to know

They may be invisible to the naked eye, but Cyclospora oocysts-tiny parasites measuring just 8 to 10 micrometers across (about one-tenth the width of a human hair) -have caused a major outbreak of an intestinal infection called cyclosporiasis across the United States since June.

"Cyclosporiasis is an intestinal illness caused by the parasite Cyclospora cayetanensis, which is transmitted mainly through ingestion of contaminated food like fresh produce (leafy greens and berries)," said Abbye Frederick, MD, a Cape Cod Healthcare infectious disease physician. "In the United States, cyclosporiasis is seasonal and occurs mainly during the summertime. The parasitic oocysts require warm environments to become infectious. Larger outbreaks can be driven by contamination of widely-distributed produce."

As of July 15, 2026, the Centers for Disease Control and Prevention (CDC) reported 1,645 cases of cyclosporiasis confirmed by lab tests across 34 states. More than 5,100 cases require further testing to confirm if they acquired cyclosporiasis in the United States.

In Massachusetts, the cyclosporiasis count remains relatively low. According to the Massachusetts Department of Public Health, 18 cases have been reported so far this year. The state's Foodborne and Waterborne Illness Report covering 2016 through 2026 shows consistently low annual case counts, with one notable exception. In 2019, Massachusetts recorded 211 cases.

According to the CDC, the age range of those with the disease was 2 to 95 years, with a median age of 44, and 56 percent were female. The average date of onset was June 22, 2026 (range from May 1 to July 9). Thus far, 141 have been hospitalized and no deaths were reported from the illness.

"Concern is warranted because cyclosporiasis outbreaks are driven by contaminated produce that is distributed in large supply chains that can reach any geographic area," Dr. Frederick said.

Symptoms and Treatment

Some of the symptoms of cyclosporiasis, according to Dr. Frederick, include:

• Watery diarrhea.
• Stomach cramping.
• Nausea.
• Fever.
• Weight loss.

Symptoms typically begin about one week after ingesting contaminated food and can be more severe in vulnerable populations, she said. The symptoms can wax and wane and can last longer than other stomach illnesses.

She said people should seek treatment if symptoms last more than a few days, especially watery diarrhea accompanied by rapid heart rate, fever, weight loss or inability to maintain hydration.

Treatment includes supportive care, including fluids, rest and antibiotics, namely trimethoprim-sulfamethoxazole, according to Dr. Frederick.

Most healthy individuals will recover on their own, but symptoms can last longer if left untreated, she said.

Unlike noroviruses and other intestinal illnesses, which spread easily from person to person and cause sudden illness after a short incubation period, cyclosporiasis is usually not spread through direct person-to-person contact.

Prevention

Precautions include:

• Thoroughly washing all fresh produce.
• Following public health advisories.
• Cooking your food.

Outbreaks linked to domestically-grown produce can occur. Locally-sourced produce with good sanitation practices may carry lower risk, but it is not risk-free, Dr. Frederick said. "The most reliable risk reduction is through washing your produce and cooking your food."