Influenza viruses that infect birds are called “avian influenza viruses”. Only influenza A viruses infect birds. All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats; however, there are substantial genetic differences between the subtypes that typically infect both people and birds. Although avian influenza A viruses do not usually infect humans, several instances of human infections and outbreaks of avian influenza have been reported since 1997. Most cases of avian influenza infection in humans are thought to have resulted from contact with infected poultry or contaminated surfaces. There is still a lot to learn about how different subtypes and strains of avian influenza viruses might affect humans. Because of concerns about the potential for more widespread infection in the human population, public health authorities closely monitor outbreaks of human illness associated with avian influenza. To date, human infections with avian influenza viruses detected since 1997 have not resulted in sustained human-to-human transmission. However, because influenza viruses have the potential to change and gain the ability to spread easily between people, monitoring for human infection and person-to-person transmission is important.

From December 2014 to June 2015, the United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) and the U.S. Department of the Interior (DOI), National Wildlife Health Center detected and reported highly pathogenic avian influenza (HPAI) H5 viruses in U.S. domestic poultry (backyard and commercial flocks), captive wild birds, and wild birds. The HPAI H5 influenza A viruses detected in US domestic poultry, captive wild birds and wild birds were H5N8, H5N2, and a new H5N1 virus that had a combination of genes from HPAI H5N1 viruses that spread in Asia and low-pathogenic avian influenza viruses that circulate in wild birds in North America. No human infections with these viruses were detected; however, similar viruses have infected people.

As of June 15, 2017, 859 laboratory–confirmed avian influenza A (H5N1), not the newly detected H5N1, infections in humans resulting in 453 deaths have been reported to the World Health Organization (WHO) from 16 countries. No human infections with avian influenza A (H5N1) have been identified in the United States. For updates on avian influenza, visit the CDC's Information on Bird Flu website and the WHO's Influenza (Avian and other zoonotic) website.

There have also been avian influenza (not H5N1) outbreaks reported in the US.  In January 2016, an outbreak of HPAI (H7N8) virus was reported in a commercial turkey flock in Dubois County, Indiana. 

Low pathogenic avian influenza (LPAI) (H7N8) was subsequently detected in eight nearby turkey flocks. No transmission of HPAI (H7N8) or LPAI (H7N8) virus to humans was reported.

Two outbreaks of high pathogenic avian influenza (HPAI) (H7N9) were reported in Lincoln County, Tennessee in March 2017. In addition, five states, Georgia, Wisconsin, Tennessee, Alabama and Kentucky, reported cases of low pathogenic avian influenza (LPAI) (H7N9) during 2017. One outbreak of LPAI (H5N2) was reported in Wisconsin in 2017. 

In addition, two avian influenza (not H5N1) outbreaks occurred among poultry populations in southeast and northeast Texas in February and May 2004, respectively. No human cases of influenza occurred from these poultry outbreaks.

In April 2013, China began reporting human cases of avian influenza A (H7N9). As of June 15, 2017, there have been 1533 laboratory-confirmed cases of avian influenza A (H7N9), including at least 592 deaths, reported to the World Health Organization. Most human cases are associated with exposure to infected live poultry or contaminated environments, including markets where live poultry is sold. Information to date suggests that these viruses do not transmit easily from human to human.

In December 2016, New York City detected cases of avian influenza A (H7N2) among cats in an animal shelter. There was one confirmed human case associated with the outbreak. The person had mild symptoms and recovered. There were no cases of person-to-person transmission reported.