Chipotle Mexican Grill’s stock is dropping like a rock today after reports of several cases of norovirus infections among customers of one of the chain’s Los Angeles locations.

The Los Angeles Health Department has confirmed it knows about the reports. The department activated its Acute Communicable Disease Control unit to investigate the situation.

It’s too early in the investigation for the health department to speculate on the scope of the possible outbreak. At least five people in two separate dining parties reported classic symptoms of norovirus infection after eating at the restaurant on or around Dec. 13, according to the website iwaspoisoned.com.

The website, founded by Patrick Quade, has accurately identified several foodborne illness outbreaks associated with restaurants, including an outbreak in July linked to a Chipotle restaurant in Sterling, VA.

Chipotle’s spokesman Chris Arnold said the Denver-based burrito chain is aware of three reports about the Los Angeles restaurant at 4550 W. Pico Blvd. He said none of the implicated customers have contacted the company. Even though there is “no clinical validation” for the reported illnesses, Chipotle launched “heightened” sanitization efforts at the restaurant.

Bloomberg news is reporting the beleaguered company’s stock is tumbling today, with shares down at least 3.4 percent as of midday.

“The latest report sent the shares down as much as 3.4 percent to $302.60, marking the biggest intraday drop since Nov. 13. Even before the decline, the stock had fallen 17 percent this year,” Bloomberg reported.

A series of outbreaks among hundreds of Chipotle customers across the country in the last six months of 2015 started the company’s fall from more than $750 per share in July that year to less than half that by January 2016. those outbreaks included bacterial pathogens as well as norovirus.

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