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. 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. Regardless of pathogenicity assessments in birds, Asian lineage LPAI A(H7N9) virus typically causes severe illness in infected humans.
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. 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. Nosocomial transmission, including patient-to-healthcare worker, and patient-to-patient, has been reported for Asian lineage LPAI A(H7N9) viruses.
History and exam
Key diagnostic factors
- typical influenza signs and symptoms
- decreased breath sounds
Other diagnostic factors
- vomiting, diarrhea
- altered mental status
- environmental exposure to Asian lineage A(H7N9) virus
- close contact with infected humans
- laboratory work with A(H7N9) virus
1st investigations to order
- CBC with differential
- liver function tests (alkaline phosphatase, hepatic aminotransferases, bilirubin)
- pulse oximetry
- sputum Gram stain
- sputum and blood bacterial culture
- reverse transcription polymerase chain reaction (RT-PCR) of respiratory specimens for Asian lineage A(H7N9) virus and influenza A and B viruses
Investigations to consider
- viral culture of respiratory specimens
- serologic testing for A(H7N9)-specific antibody for retrospective diagnosis
unprotected exposed healthcare workers and close contacts of suspected/confirmed case
Jake Dunning, BSc (Hons), MBBS, MRCP, PhD
Consultant in Infectious Diseases and General (Internal) Medicine
Tuberculosis; Acute Respiratory, Gastrointestinal, Emerging and Zoonotic Infections; and Travel Health (TARGET) Division
National Infection Service
Public Health England
JD declares that he has no competing interests.
Justin R. Ortiz, MD, MS
Associate Professor of Medicine
Center for Vaccine Development and Global Health
University of Maryland School of Medicine
JRO is a member of the International Council on Adult Immunization and the scientific community for the Global Influenza Hospitalization Surveillance Network.
Timothy M. Uyeki, MD, MPH, MPP
Chief Medical Officer
National Center for Immunization and Respiratory Diseases
Centers for Disease Control and Prevention
TMU is a member of the Guideline Development Group for the World Health Organization Standard Guidance for the Clinical Management of Severe Influenza. TMU is a co-chair for the Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 update on diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza.
Rob Fowler, MDCM, MSc
Sunnybrook Health Sciences Centre
RF declares that he has no competing interests.
Nelson Lee, MD, FRCP(Lond.), FRCP(Edin.)
Division of Infectious Diseases
Faculty of Medicine and Dentistry
University of Alberta
NL declares that he has no competing interests.
Michael Ison, MD, MS
Division of Infectious Diseases
Division of Organ Transplantation
Northwestern University Feinberg School of Medicine
MI declares that he received research support, paid to Northwestern University, from Beckman Coulter, Chimerix, and Gilead; is a paid consultant for Celltrion, Chimerix, Farmark, Genentech/Roche, Toyama/MediVector, Seqirus, and Shionogi; and is a member of the DSMB for GlaxoSmithKline and Shionogi.
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