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Chipotle's shares dropped more than six percent Tuesday as investors responded to the incident with concern.
Symptoms of norovirus include nausea, vomiting, stomach pain and diarrhea.
In 2015, Chipotle's revenue and reputation suffered after an E. coli outbreak at restaurants in nine states and a norovirus outbreak at a Boston location. Approximately 500 customers reported illnesses.
"We may be at a higher risk for food-borne illness outbreaks than some competitors due to our use of fresh produce and meats, rather than frozen, and our reliance on employees cooking with traditional methods rather than automation," Chipotle officials said at the time.
According to the Centers for Disease Control and Prevention, restaurant workers are often the source of norovirus outbreaks, as they often touch foods such as raw fruits and vegetables with their bare hands before serving them.
In 2016, Chipotle shut down all locations for a day retrain employees on food safety.