We’ve all made mistakes at work. But, thankfully, no mistake you’ve ever made not only cost your company a neat $1 billion in value, but also given more than 135 people diarrhea — we assume so, at least… We don’t know about your screw ups!

Chipotle believes that their $1 billion losses over five days could be traced back to a single employee coming to work sick. They believe that the Patient Zero employee was responsible for spreading norovirus at a Washington, DC-area Chipotle, where more than 135 people have fallen ill with the stomach bug.

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According to WebMD, norovirus is highly contagious — and has been known to spread through crowded places such as cruise ships and classrooms “leaving vomiting, diarrhea, and stomach cramps in its wake.” Symptoms usually begin to show up 12 to 48 hours after the first exposure to the virus — in this case, exposure to the contaminated food — and can last from one to three days.

In a statement, the Mexican chain’s founder and CEO Steve Ells said the company was able to to trace the root of the problem. “We conducted a thorough investigation and it revealed that our leadership didn’t follow our protocols,” he said on a conference call following five days of decline for the company’s stock. “We believe someone was working while sick.”

steve ells getty images

Chipotle CEO Steve Ells.

The people fell sick between July 13 and July 16, and shortly thereafter, on July 18, Chipotle’s stock dipped 7.8 percent. One of the ill-fated customers wrote in a report, “I ate at Chipotle on Saturday, July 15, around 6 p.m. I had a chicken burrito with black beans, brown rice, corn, salsa, cheese, and lettuce. Monday night around 11 p.m., I began having severe stomach pain and by 3 a.m. had non-stop diarrhea… Now (Wednesday), I’m weak and tired with no appetite.”

In a statement to the International Business Times, a spokesperson for Chipotle confimed they were working with the Health Department to rectify the situation. The statement read, “Norovirus is common and easily transmitted by human contact, and this incident is not sugestive of any supply chain issues.”

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