Avian influenza A (H7N9) virus infection

The epidemic has been geographically focused in China, and is associated with exposure to infected poultry.

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 40% among hospitalized patients with laboratory-confirmed infection.

Reverse transcription-polymerase chain reaction of respiratory tract samples is the recommended diagnostic test.

Treatment involves supportive care, specialized intensive-care management, and 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]Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus; Abdel-Ghafar AN, Chotpitayasunondh T, Gao Z, et al. 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-pathogenicity 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 (herein 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. February 2017 [internet publication]. http://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.jfma-online.com/article/S0929-6646(17)30149-3/fulltext 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.ncbi.nlm.nih.gov/pmc/articles/PMC3801178/ 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://www.ncbi.nlm.nih.gov/pmc/articles/PMC3957952/ http://www.ncbi.nlm.nih.gov/pubmed/24403589?tool=bestpractice.com  Investigation of isolated clusters of human infections where zoonotic transmission was thought to be unlikely suggests that human-to-human transmission may occur with Asian lineage LPAI A(H7N9) viruses, although transmission appears to be limited and nonsustainable.[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.jfma-online.com/article/S0929-6646(17)30149-3/fulltext 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.ncbi.nlm.nih.gov/pmc/articles/PMC3805478/ 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://www.ncbi.nlm.nih.gov/pmc/articles/PMC5139097/ http://www.ncbi.nlm.nih.gov/pubmed/27919225?tool=bestpractice.com  Nosocomial transmission, including patient-to-healthcare worker, and patient-to-patient, has been reported for Asian lineage LPAI A(H7N9) viruses.[10]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 [11]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.ncbi.nlm.nih.gov/pmc/articles/PMC4652199/ http://www.ncbi.nlm.nih.gov/pubmed/26586515?tool=bestpractice.com [12]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://www.ncbi.nlm.nih.gov/pmc/articles/PMC4806937/ http://www.ncbi.nlm.nih.gov/pubmed/26982379?tool=bestpractice.com