(Reuters) – Chipotle Mexican Grill Inc (CMG.N) closed a restaurant in Virginia due to a suspected norovirus outbreak among some diners, sending shares down more than 6 percent on Tuesday.

Investors are keenly sensitive to food-safety issues at Chipotle, which is still working to recover fully from a string of sales-crushing E. coli, salmonella and norovirus outbreaks in late 2015.

Chipotle’s stock was off 6.4 percent, or $23.41, at $368.60 at midday on Tuesday. The shares were trading at nearly $750 prior to the company’s previous food-safety incidents.

Chipotle spokesman Chris Arnold said on Tuesday the reported symptoms are consistent with norovirus, a highly contagious virus that can cause severe vomiting and diarrhea.

“We plan to reopen the restaurant today,” Arnold said.

The suspected illnesses were first reported by Business Insider earlier on Tuesday. It cited information from iwaspoisoned.com, a website on which consumers document what they believe are incidents of foodborne illness.

“In total, eight reports were made to the website, indicating that at least 13 customers fell sick after eating there from July 14-15,” the news site said.

Chipotle voluntarily closed the restaurant on Monday, said Victor Avitto, environmental health supervisor for the Loudoun County Public Health Department, which has jurisdiction over the restaurant on Tripleseven Road in Sterling.

Test results are expected later this week, Avitto said.