The epidemic has been geographically focused in China, and is associated with exposure to infected poultry.
Five annual epidemic waves of human cases occurred during 2013 to 2017, with the largest wave occurring in 2016 to 2017. Three sporadic human cases were reported in 2018, and only one case was reported in the first half of 2019.
The risk to public health is low; however, the pandemic potential of this virus is concerning. Case clusters of limited human-to-human transmission have been described, but there is no evidence of sustained transmission.
Infection prevention and control measures for routine care include standard, droplet, and contact precautions. Particulate respirators are recommended for aerosol-generating procedures.
There is a high cumulative case-fatality proportion of approximately 39% among hospitalized patients with laboratory-confirmed infection.
Reverse transcription polymerase chain reaction of respiratory tract samples at a designated public health laboratory is the recommended diagnostic test.
Treatment involves supportive care, specialized intensive-care management, and prompt administration of a neuraminidase inhibitor.
Avian influenza A viruses are generally confined to birds but have infected other mammals and some viruses have crossed the species barrier to sporadically infect humans. Highly pathogenic avian influenza (HPAI) A(H5N1) virus is capable of causing severe multisystem disease in birds, humans, and other mammals.[1]Abdel-Ghafar AN, Chotpitayasunondh T, Gao Z, et al; Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus. Update on avian influenza A (H5N1) virus infection in humans. N Engl J Med. 2008 Jan 17;358(3):261-73.
https://www.nejm.org/doi/10.1056/NEJMra0707279
http://www.ncbi.nlm.nih.gov/pubmed/18199865?tool=bestpractice.com
Until 2017, Asian lineage A(H7N9) virus infections in birds were associated with only asymptomatic infection or mild illness (characterized as low-pathogenic avian influenza [LPAI]). In February 2017, the detection of Asian lineage HPAI A(H7N9) viruses was reported for the first time in the People’s Republic of China (hereafter referred to as China), in samples from human cases, and from poultry and their environments.[2]World Health Organization. Human infection with avian influenza A(H7N9) virus - China. Feb 2017 [internet publication].
https://www.who.int/csr/don/27-february-2017-ah7n9-china/en/
[3]Yang JR, Liu MT. Human infection caused by an avian influenza A (H7N9) virus with a polybasic cleavage site in Taiwan, 2017. J Formos Med Assoc. 2017 Mar;116(3):210-2.
https://www.sciencedirect.com/science/article/pii/S0929664617301493
http://www.ncbi.nlm.nih.gov/pubmed/28259506?tool=bestpractice.com
Regardless of pathogenicity assessments in birds, Asian lineage LPAI A(H7N9) virus typically causes severe illness in infected humans.[4]Yu H, Cowling BJ, Feng L, et al. Human infection with avian influenza A H7N9 virus: an assessment of clinical severity. Lancet. 2013 Jul 13;382(9887):138-45.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)61207-6/fulltext
http://www.ncbi.nlm.nih.gov/pubmed/23803487?tool=bestpractice.com
Following the detection of Asian lineage LPAI A(H7N9) virus infection in humans in eastern China in March 2013, A(H7N9) viruses that are genetically similar to isolates from human cases were detected in poultry and environmental samples obtained from live animal markets in China.[5]Chen Y, Liang W, Yang S, et al. Human infections with the emerging avian influenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome. Lancet. 2013 Jun 1;381(9881):1916-25.
http://www.ncbi.nlm.nih.gov/pubmed/23623390?tool=bestpractice.com
[6]Yu X, Jin T, Cui Y, et al. Influenza H7N9 and H9N2 viruses: coexistence in poultry linked to human H7N9 infection and genome characteristics. J Virol. 2014 Mar;88(6):3423-31.
https://jvi.asm.org/content/88/6/3423.long
http://www.ncbi.nlm.nih.gov/pubmed/24403589?tool=bestpractice.com
Investigations of isolated clusters of human infections where zoonotic transmission was thought to be unlikely suggest that human-to-human transmission may occur with Asian lineage LPAI A(H7N9) viruses, although transmission appears to be limited and nonsustainable to date.[3]Yang JR, Liu MT. Human infection caused by an avian influenza A (H7N9) virus with a polybasic cleavage site in Taiwan, 2017. J Formos Med Assoc. 2017 Mar;116(3):210-2.
https://www.sciencedirect.com/science/article/pii/S0929664617301493
http://www.ncbi.nlm.nih.gov/pubmed/28259506?tool=bestpractice.com
[7]Li Q, Zhou L, Zhou M, et al. Epidemiology of human infections with avian influenza A(H7N9) virus in China. N Engl J Med. 2014 Feb 6;370(6):520-32.
https://www.nejm.org/doi/10.1056/NEJMoa1304617
http://www.ncbi.nlm.nih.gov/pubmed/23614499?tool=bestpractice.com
[8]Qi X, Qian YH, Bao CJ, et al. Probable person to person transmission of novel avian influenza A (H7N9) virus in Eastern China, 2013: epidemiological investigation. BMJ. 2013 Aug 6;347:f4752.
https://www.bmj.com/content/347/bmj.f4752.long
http://www.ncbi.nlm.nih.gov/pubmed/23920350?tool=bestpractice.com
[9]Xiang N, Iuliano AD, Zhang Y, et al. Comparison of the first three waves of avian influenza A(H7N9) virus circulation in the mainland of the People's Republic of China. BMC Infect Dis. 2016 Dec 5;16(1):734.
https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-016-2049-2
http://www.ncbi.nlm.nih.gov/pubmed/27919225?tool=bestpractice.com
[10]Wang X, Wu P, Pei Y, et al. Assessment of human-to-human transmissibility of avian influenza A(H7N9) virus across 5 waves by analyzing clusters of case patients in mainland China, 2013-2017. Clin Infect Dis. 2019 Feb 1;68(4):623-31.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6355824/
http://www.ncbi.nlm.nih.gov/pubmed/29961834?tool=bestpractice.com
[11]Zhou L, Chen E, Bao C, et al. Clusters of human infection and human-to-human transmission of avian influenza A(H7N9) virus, 2013-2017. Emerg Infect Dis. 2018 Feb 17;24(2):397-400.
https://wwwnc.cdc.gov/eid/article/24/2/17-1565_article
http://www.ncbi.nlm.nih.gov/pubmed/29165238?tool=bestpractice.com
Nosocomial transmission, including patient-to-healthcare worker, and patient-to-patient, has been reported for Asian lineage LPAI A(H7N9) viruses.[12]Farooqui A, Liu W, Zeng T, et al. Probable hospital cluster of H7N9 influenza infection. N Engl J Med. 2016 Feb 11;374(6):596-8.
https://www.nejm.org/doi/10.1056/NEJMc1505359
http://www.ncbi.nlm.nih.gov/pubmed/26863372?tool=bestpractice.com
[13]Fang CF, Ma MJ, Zhan BD, et al. Nosocomial transmission of avian influenza A (H7N9) virus in China: epidemiological investigation. BMJ. 2015 Nov 19;351:h5765.
https://www.bmj.com/content/351/bmj.h5765.long
http://www.ncbi.nlm.nih.gov/pubmed/26586515?tool=bestpractice.com
[14]Chen H, Liu S, Liu J, et al. Nosocomial co-transmission of avian influenza A(H7N9) and A(H1N1)pdm09 viruses between 2 patients with hematologic disorders. Emerg Infect Dis. 2016 Apr;22(4):598-607.
https://wwwnc.cdc.gov/eid/article/22/4/15-1561_article
http://www.ncbi.nlm.nih.gov/pubmed/26982379?tool=bestpractice.com