flu

Fever, muscle aches, nausea — these are what we usually associate with having the flu.

But just because you don't exhibit these symptoms, it doesn't mean you don't have the flu, researchers say. And you could be just as contagious. In fact, their study found that roughly three-quarters of people with seasonal or pandemic flu show either no symptoms or mild ones that aren't usually linked to flu.

We usually think of the flu as an illness that afflicts the elderly. But this season the virus seems to be hitting younger people hard.

This winter at Duke University Medical Center in Durham, N.C., the median age of people hospitalized with influenza was 28.5 years. Many of the worst cases of flu occurred in young, otherwise healthy people.