Avian influenza A (H5N1) virus infection

Avian influenza A(H5N1) virus infection is a notifiable condition. Infection prevention and control measures such as patient isolation and standard, contact, and airborne (including eye protection) precautions are recommended.

Sporadic human infections have been reported globally since 1997; however, there has been no evidence of sustained human-to-human transmission.

High case-fatality proportion of approximately 49% among reported cases of laboratory-confirmed infection.

Most patients present with fever and features of lower respiratory tract infection on admission to the hospital. Infection should be considered in anyone showing signs or symptoms of acute respiratory illness or conjunctivitis who has a relevant exposure history. Molecular testing (with subtyping) is recommended to confirm the diagnosis.

Antiviral therapy is recommended as soon as possible in symptomatic patients with suspected or confirmed infection. Supportive care and specialized intensive care management are indicated for respiratory failure and other severe complications.

Antiviral postexposure prophylaxis and monitoring of close contacts of a confirmed or probable case are recommended.

Avian influenza A(H5N1) is a contagious disease of wild birds and poultry. Avian influenza A viruses can either be low or highly pathogenic, and can infect other animal species such as wild or domestic terrestrial mammals, and marine mammals.​ Different virus subtypes have sporadically infected humans to cause a wide range of pathologies. Specifically, highly pathogenic avian influenza (HPAI) A(H5N1) virus originating in poultry and wild birds can be transmitted to humans, with rare cases of infection transmitted between humans.[1]Ungchusak K, Auewarakul P, Dowell SF, et al. Probable person-to-person transmission of avian influenza A (H5N1). N Engl J Med. 2005 Jan 27;352(4):333-40. https://www.nejm.org/doi/10.1056/NEJMoa044021 http://www.ncbi.nlm.nih.gov/pubmed/15668219?tool=bestpractice.com [2]Wang H, Feng Z, Shu Y, et al. Probable limited person-to-person transmission of highly pathogenic avian influenza A (H5N1) virus in China. Lancet. 2008 Apr 26;371(9622):1427-34. http://www.ncbi.nlm.nih.gov/pubmed/18400288?tool=bestpractice.com Cases of human infection linked to infected dairy cows have been reported, and represent the first instances of likely mammal-to-human transmission.[3]Centers for Disease Control and Prevention. Avian influenza (bird flu): current situation: bird flu in dairy cows. Jul 2025 [internet publication]. https://www.cdc.gov/bird-flu/situation-summary/mammals.html ​​

This topic focuses on human infection with HPAI A(H5N1) virus; Avian influenza A(H7N9) virus infection is covered in a separate topic.​