The highly contagious illness is linked to a parasite, usually found in food or water.
Illinois health officials say they're seeing an uptick in cases of cyclosporiasis.
So far 141 cases are confirmed statewide.
Of those, 62 reported travel outside the U.S., 59 were domestically acquired and 20 cases are pending investigation to determine travel status.
The epicenter of the outbreak seems to be Michigan.
Kristin Gustashaw is a clinical dietician at Rush. She shared some ways to keep from getting sick Tuesday.
Dozens of cases of contagious parasite reported in Illinois
"IDPH is seeing a higher-than-average number of reported cases of cyclosporiasis, consistent with what is being seen in several other states. It can be contracted by consuming food or water contaminated with feces. At this point, no single source or cause of this increase has been identified, and there is no evidence of a large outbreak accounting for all or most of these cases. IDPH continues to work with the CDC and other public health partners to look for trends. In the meantime, IDPH recommends following all guidelines for safe food handling, including washing produce (wash all fruits and vegetables under running water before eating, cutting, or cooking; scrub firm produce such as melons and cucumbers with a clean produce brush)," the Illinois Department of Public Health said.
"It's usually related to contaminated water. And that's why it's an issue with vegetables and berries and this type of thing," said Dr. Lynwood Jones, with Ascension St. Alexius Hospital.
Jones is an infectious disease expert who says it's not usual to see cases like this in the Chicago area.
"It may be two days to two weeks before you know it's happened, which is rather hard to track the problem. What have I been exposed to in the last two weeks?" Gustashaw said.
Other symptoms can include abdominal pain, low-grade fever and bloating.
"We can't kill it by water or some chemical. The only way to kill it is to cook it," Gustashaw said.
But you can wash it off.
"I tell people you when they're out picking berries, don't eat them then. Take them home and wash them," Jones said.
Health officials say it's possible there are more cases than they are aware of because many of those who have had it may not come to a hospital or a doctor for treatment.