New CDC data indicates a rise in cases of norovirus, often colloquially referred to as "stomach flu." Test positivity has spiked.

Ah, the classic signs of winter: Freezing temperatures, icy roads and empty tissue boxes. It's no secret that winter is a time when illness is prominent. Coughs, colds, and viruses are seemingly running rampant this time of year. This is thanks to the drier air and an influx of time spent indoors, according to the Mayo Clinic.

This winter's wave of norovirus infections has reached levels that are now more than double last season's peak, in figures published Monday by the Centers for Disease Control and Prevention tracking the notorious stomach bug.

Norovirus is a very infectious gastrointestinal virus and is also the leading cause of foodborne illness in the U.S.