It's a virus that young children can get, I'm not sure if adults get it but it sounds rare for an adult to get it. It's always going around for children though.
It's basically just severe and constant duking and can lead to severe dehydration as was the case with my nephew. It was pretty ed up when he got it because he was still a baby and he actually started turning blue when we called 911, they had to come and put the oxygen and all that on him. I think the saddest I've ever been in my life was watching that happen.