I’ve been a fan of Nate Silver’s fivethirtyeight.com for a few years. It’s one of a handful of sites that I read daily. Today the numbers nerds tackled the Chipotle norovirus outbreak comparing it to other fast food outbreaks using CDC’s databases. Turns out this outbreak is unique for its size and location – at a fast food setting.

Just under 3 percent of the food-related norovirus outbreaks that the Centers for Disease Control and Prevention tracked from 2009 to 20141sickened 80 or more people. Only 1.3 percent of outbreaks sickened 140 or more people. Half of all outbreaks sickened 11 or fewer people.

It’s not just the size of the outbreak that’s unusual — it’s where it happened. Although norovirus is the most common cause of food-related illnesses nationwide (about 50 percent of outbreaks), it’s not the most common cause of illnesses at fast-food outlets like Chipotle. Since 2009, when the CDC began tracking where outbreaks occurred, fast-food restaurants have been much more likely to give their patrons salmonella than norovirus (28 percent of illnesses at fast-food chains were linked to norovirus, while 43 percent were linked to salmonella). Sit-down restaurants have the opposite risk profile (45 percent of illnesses linked to norovirus, 25 percent to salmonella).

And here’s some more context from CDC on where norovirus outbreaks happen.