Brittani Leone, 31, a nurse in Pittsburgh, said a cyclospora infection hit her “out of nowhere” on July 13. She had just finished dinner with her husband when she lurched toward the bathroom. For five days, she said, she stayed more or less anchored to the toilet, able to eat only Popsicles and toast. When the symptoms faded, she celebrated by ordering Italian wedding soup. Less than an hour after eating, she said, “it all started again.” She endured another week of symptoms that came and went, including a resurgence of diarrhea.

About two weeks after her initial symptoms, she got an antibiotic and quickly started to feel better. She’s still weak, she said, as if her limbs are too heavy, and her head feels foggy. She took a leave of absence from work on her doctor’s recommendation. But she has been free of diarrhea since she started treatment.

Since 2016, the Centers for Disease Control and Prevention has reported an average of about 2,800 cyclospora cases per year in the United States; in 2026, the agency confirmed around 10,400 cases since May 1 and is investigating more than 12,000 additional cases in states across the country.

Dr. Cory Fisher, a family medicine physician with the Cleveland Clinic in Ohio, said he didn’t have a good sense of how often cyclospora symptoms recur. During a typical year, he said, he sees cyclospora patients “almost never.” This summer, he’s treated about two dozen of them.

Cyclospora infections can vary in duration and severity, Dr. Gulick said. Some people fight off the parasite without treatment and with minimal symptoms. Other people end up with diarrhea — either constant or intermittent — for more than a month. On average, symptoms last about three weeks without treatment, Dr. Gulick said, although antibiotics can shorten the duration.