Infection Risk for Persons Exposed to Highly Pathogenic Avian Influenza A H5 Virus–Infected Birds, United States, December 2014–March 2015


Newly emerged highly pathogenic avian influenza (HPAI) A H5 viruses have caused outbreaks among birds in the United States. These viruses differ genetically from HPAI H5 viruses that previously caused human illness, most notably in Asia and Africa.

To assess the risk for animal-to-human HPAI H5 virus transmission in the United States, we determined the number of persons with self-reported exposure to infected birds, the number with an acute respiratory infection (ARI) during a 10-day postexposure period, and the number with ARI who tested positive for influenza by real-time reverse transcription PCR or serologic testing for each outbreak during December 15, 2014–March 31, 2015.

During 60 outbreaks in 13 states, a total of 164 persons were exposed to infected birds. ARI developed in 5 of these persons within 10 days of exposure. H5 influenza virus infection was not identified in any persons with ARI, suggesting a low risk for animal-to-human HPAI H5 virus transmission.

HPAI H5 virus outbreaks in US birds will likely continue, and additional reassortment with North American viruses may also occur. Although the risk of virus transmission to humans appears to be low, each exposure incident should be reported immediately and investigated collaboratively by animal and human health partners. A rapid response to any potential human cases of HPAI H5 infection in the United States is critical to prevent further cases, evaluate clinical illness, and assess the ability of these viruses to spread among humans.