The norovirus hit Minnehaha Accademy last week, sickening dozens of people and forcing the Minneapolis school to close temporarily.
Some 20 million people are sickened by norovirus in the U.S. each year, and they experience symptoms like vomiting, diarrhea and abdominal cramps.
Norovirus isn't a serious illness. It usually lasts one to three days.
But it can dehydrate people and it hits quick — symptoms start within a day or two of being exposed.
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What's more, it's super contagious. After an outbreak like the one at Minnehaha, you have to clean everything.
Hard surfaces contaminated with norovirus can be infectious for months after an outbreak, said Dr. Jon Hallberg, MPR News regular medical analyst.
To avoid further illnesses, "you basically have to wipe everything down," Hallberg said.
That's why Minnehaha closed for a while: Outbreaks require facilities like schools to be cleared out and cleaned up.
For more on the norovirus, use the audio player above.