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.

Norovirus, also known as the stomach bug, is spreading across the U.S. Here's what to know about the contagious virus and how best to prevent an infection.