As China experiences a rise in respiratory infections this winter, one little-known virus has gotten a lot of attention – and some people may worry whether the rise in cases could be felt more broadly around the world.

As China continues to monitor an increase in cases of human metapneumovirus (HMPV), here's what you need to know about the illness.

Plenty of viruses are having their strongest season for years. But experts have urged calm about HMPV, which is not a new disease — even if you've never heard about it.