Those infected with the flu are most contagious during the first three days, the CDC said. In some cases, however, people can spread the flu even before experiencing symptoms or up to five to seven days after they appear. Young people and those with weaker immune systems can experience symptoms for a longer period.

As cases of flu have reached their highest level in 25 years in the U.S., doctors are warning Americans that symptoms of this year’s strain are different from those seen in previous years.

A new flu strain is surging nationwide. Ohio reports hospitalizations doubling as cases rise. Learn the symptoms and prevention tips.

Is it flu A or flu B, and how long is it contagious? Here's what to know about the flu virus running rampant in New Jersey, symptoms, more.

The new, virulent flu strain has sent more than 100,000 to the hospital. Here's what to know, how to check infections rates near you.

Subclade K, which is circulating in Arizona, has been dubbed a 'super flu' but some experts say that's not an accurate characterization.

With multiple viruses circulating, doctors say it can be difficult to determine which illness someone has based on symptoms alone.

While the new findings are encouraging, "vaccines won’t do any good if people don’t get them," one expert said.