Chipotle conducted a complete sanitation of its store on Monday in Sterling, Virginia, after 13 diners who ate at the popular Mexican grill restaurant became sick. The symptoms of the affected customers -- who dined between July 14 and July 15 -- were consistent with norovirus, Jim Marsden, the head of food safety of Chipotle, said.

The popular food chain is working with health authorities to understand the cause of the ailment and to resolve the problem as soon as possible, Marsden said in a statement. He added that Chipotle voluntarily shuttered on Monday its Sterling outlet to conduct the complete sanitization, but the restaurant would reopen, NBC reported.

Stocks plummet

After the report of the restaurant’s closure and customers becoming ill, shares of Chipotle dipped by up to 7.5 percent, The New York Post reported. By midday trading, the stock shed $23.43, or 5.7 percent, to $369.57.

Chipotle’s share price has almost halved from a peak of almost $750 before the popular Mexican grill restaurant -- where former U.S. President Barack Obama and his family used to dine – was hit by a food scare in 2015. Yuki Noguchi, an analyst with NPR, explained that it is an especially sensitive issue for Chipotle when its customers became sick after they dined at the restaurant “which struggled with recurring problems with foodborne illnesses two years ago that caused its stock price to plummet,” NPR reported.

When Chipotle suffered from food safety two years ago, the restaurant was linked to other types of outbreaks that hit several locations of the food chain across the U.S., including salmonella and E.

Top Videos of the Day

coli. The symptoms shown by customers who had eaten at Chipotle’s Sterling store are consistent with norovirus, a highly contagious virus.

Human carrier

Since the health department of Loudon County, where the affected Sterling store is located, is not aware of any serious ailment of any contaminated food, the health director of the county said that the virus was likely spread by a human carrier. In December 2015, a Chipotle restaurant in Boston recorded a norovirus outbreak. After 120 college students ate at the outlet, they reported symptoms of norovirus. The symptoms of the diners who ate at the Chipotle Sterling restaurant include diarrhea, nausea, fever, and vomiting.

In 2015, it was an E. coli scare that hit Chipotle stores in 14 states. After the Mexican grill restaurant put in place new safety measures to prevent another outbreak in the future, the Food and Drug Administration declared the outbreak as apparently over in February 2016.