Shares of Chiptole Mexican Grill plummeted Tuesday after the burrito chain operator confirmed it closed a store in Northern Virginia following "a small number of reported illnesses," renewing past food safety concerns that have troubled the company in the last few years.

The reported symptoms are consistent with norovirus, the Denver-based company said. Norovirus is a common cause of viral gastroenteritis.

"Norovirus does not come from our food supply, and it is safe to eat at Chipotle," said Jim Marsden, Chipotlet's executive director of food safety in a statement. "We are working with health authorities to understand what the cause may be and to resolve the situation as quickly as possible,"

Chipotle closed the store, located on Tripleseven Road in Sterling, Va., about 20 miles west of Washington, D.C., on Monday to conduct "complete sanitization," and plans to reopen it later today.

Shares of Chipotle were down 6.6% to 366.83 in early afternoon trading.

Chipotle has been working to bounce back from food scares that included an E. coli outbreak in the fall of 2015 and included a norovirus case in Boston later that year. The efforts have included tweaks to cooking procedures and training for employees to prevent such cases.

Norovirus is the leading cause of illness and outbreaks from contaminated food in the United States, according to the Centers for Disease Control and Prevention. Infected employees are frequently the source of the outbreaks, the CDC says, often by touching foods such as raw fruits and vegetables with their bare hands before serving them. Symptoms include nausea, stomach pain and diarrhea.

Contributing: The Associated Press