In its announcement this week of the first human death from bird flu in the United States, health officials in Louisiana were quick to note that the patient was over age 65 and “reported to have underlying medical conditions.

The patient, who was older than 65 and had underlying medical conditions, was hospitalized weeks ago in critical condition with severe respiratory illness.

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.