Chipotle closed one of its restaurants in order to perform "a complete sanitization” on Monday after rumors of a Foodborne Illness Outbreak appeared on social media. On Tuesday, Chipotle confirmed that it had received numerous reports of customers getting sick after eating at one of the chain’s locations in Sterling, Virginia.

In a statement to NBC News, Jim Marsden, Chipotle’s head of food safety, said that the symptoms the sick customers reported were consistent with norovirus. Norovirus is extremely contagious and is the most common foodborne illness in the United States.

According to the Centers for Disease Control and Prevention, norovirus infects between 19 and 21 million people per year. Marsden was quick to reassure concerned consumers: "We are working with health authorities to understand what the cause may be and to resolve the situation as quickly as possible… Norovirus does not come from our food supply, and it is safe to eat at Chipotle.”

This is not Chipotle's first outbreak

This incident adds to the growing list of foodborne illness outbreaks at Chipotle restaurants since 2015. In August 2015, 207 people became ill after eating at a California Chipotle location, sparking a federal inquiry into the chain’s food safety procedures. A Boston Chipotle location experienced an outbreak of norovirus in December 2015, in which 80 college students fell ill.

One month prior, restaurants in multiple states were hit with an outbreak of E. coli, causing 40 locations in Washington and Oregon to close temporarily.

How will this outbreak impact Chipotle?

Despite these incidents, Chipotle’s efforts to improve food safety were initially drawing customers back to the chain. The Washington Post reports that Chief Marketing Officer of Chipotle, Mark Crumpacker, said during a conference call with investors in December 2016 that “the data, everything that we have, suggest there are not large numbers of customers staying away from Chipotle.”

However, this trend may be reversing in the wake of the Virginia norovirus outbreak.

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According to CNBC, Chipotle’s shares have plummeted over five percent since this most recent outbreak. Managing director of GlobalData, Neil Saunders, claimed in an interview with CNBC that this incident, though isolated to one Chipotle location, may harm the chain’s image. Saunders went on to say that even though Chipotle has been working to overcome recent issues, this norovirus outbreak is the latest in a long list of incidents which reflect poorly on the chain.