The entire concept of McDonald’s serving salad has always seemed wrong and unnatural, but now you have a health reason to only ever eat Big Macs: 163 people in 10 states have been made ill by salad contaminated with fecal matter. That’s poop. Your salad has poop on it.

It’s not just a mild stomach bug, either. The Food and Drug Administration has said that the problem is caused by the Cyclospora parasite. While healthy individuals should recover from a cyclospora infection without treatment, patients with weakened immune systems can be at a higher risk, and three people have been reported hospitalized so far.

The illnesses are a result of a tainted batch of lettuce from a McDonald’s supplier in Streamwood, Illinois, according to the company. “We have removed lettuce blend provided by Fresh Express’ Streamwood, Illinois, facility,” McDonald’s told USA Today. “Many restaurants already have a new lettuce blend supply, while we expect all identified restaurants will have new supply in the next few days.”

The bad news is that replacing the infected lettuce won’t stop new cases from developing overnight. The infection takes at least a week or two to take hold, according to the CDC, and it may be up to six weeks before patients experience symptoms. The most common symptom is watery diarrhea, although patients might also experience a loss of appetite, weight loss, cramping, nausea, and fatigue.

“McDonald’s is committed to the highest standards of food safety and quality and we continue to cooperate and support regulatory and public health officials in their investigations,” the company said in a statement.