Bird flu, also known as avian influenza or H5N1, has infected more than 130 million birds over the past two years as it threatened commercial bird operations and recently led to the first human death in the United States.

Bird flu has claimed its first human in the United States, but health officials say the risk remains low and there are precautions to stay safe. They also say they’re vigilantly monitoring for signs that the risk is growing.

How deadly is the bird flu? The US has reported its first death from avian influenza, H5N1. Here's what to know about bird flu mortality rate and who is at risk.