Human infection with H3N8 avian influenza in China: WHO details and assessment

Situation at a glance

On 25 April 2022, the National Health Commission of the People’s Republic of China notified WHO of one confirmed case of human infection with an avian influenza A(H3N8) virus. This case appears to be the first reported case of human infection with an avian influenza A(H3N8) virus. No further cases have yet been detected among close contacts. Further epidemiological and virological investigation of this event is underway. Currently limited available epidemiologic and virologic information suggests that this avian influenza A(H3N8) virus has not acquired the ability of sustained transmission among humans, therefore, the risk at the national, regional and international level of disease spread among humans is assessed as low.

Description of the case

On 25 April 2022, the National Health Commission of the People’s Republic of China notified WHO of one confirmed case of human infection with an avian influenza A(H3N8) virus. The case is a 4-year-old boy from Henan Province. He developed fever, cough, shortness of breath on 5 April 2022, and was admitted to the hospital in critical condition on 10 April 2022 with severe pneumonia with respiratory failure. The case was then transferred to the ICU where antivirals were administered. Samples collected from the patient after hospitalization were tested for respiratory viruses (including influenza) and influenza A(H3N8) was detected in several samples. No other respiratory viruses were detected.

On 24 April 2022, The National Influenza Center of the Chinese Center for Disease Control and Prevention tested the specimen sent from Henan Province. It confirmed that the influenza A virus in the sample was the A(H3N8) subtype and all genes were of avian origin.

Before his onset of illness, the case had consumed chickens that were kept in the backyard but did not have direct exposure to them prior to illness onset. Clinical observation and sampling of the case’s close contacts, environment, local poultry market, and wild bird habitat were conducted, and no infection or any symptoms of illness were found. Further epidemiological and virological investigation (i.e., animals and environmental testing) of this event is underway.

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Epidemiology

This case appears to be the first reported case of human infection with an avian influenza A(H3N8) virus. No further cases have yet been detected among close contacts. There is limited information on the relatedness of the virus infecting this case to other avian influenza A(H3) viruses circulating in animals.

Influenza type A viruses are classified into subtypes according to different virus surface proteins hemagglutinin (HA) and neuraminidase (NA). So far, there are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes, with only a few of these subtypes circulating in humans (seasonal influenza). Depending on the origin host, influenza A viruses can also be classified as avian influenza, swine influenza, human influenza, etc., or other types of animal influenza viruses. When animal influenza viruses infect humans, these are called zoonotic infections.

Zoonotic influenza type A infections may cause diseases ranging from mild upper respiratory infection (fever and cough) to rapid progression to severe pneumonia, acute respiratory distress syndrome, shock, and even death.

In terms of transmission, human infections with avian and other zoonotic influenza viruses, though rare, have been reported. Human infections are primarily acquired through direct contact with infected animals or contaminated environments but do not result in the efficient transmission of these viruses between people. The primary risk factor for human infection appears to be direct or indirect exposure to infected animals or contaminated environments, such as live bird markets. Slaughtering, defeathering, handling carcasses of infected poultry, and preparing poultry for consumption are also likely to be risk factors.

Avian A(H3N8) influenza viruses are commonly detected globally in animals and represent one of the most frequently found subtypes in wild birds, causing minimal to no sign of disease in domestic poultry or wild birds. Cross-species transmission events of avian A(H3N8) influenza viruses have been reported for various mammal species, for example, equine and canine lineage of A(H3N8) viruses cause outbreaks in horses and dogs respectively.

The Chinese government has taken the following monitoring, prevention, and control measures:

• Testing of close contacts, animals, and environment around the case;
• Conducting a risk assessment;
• Strengthening joint prevention and control;
• Strengthening surveillance and epidemiological investigation;
• Treatment of the patient;
• Carrying out a study on the origin of disease;
• Public risk communication activities to improve public awareness and adoption of self-protection measures.

Currently, limited available epidemiologic and virologic information suggests that this avian influenza A(H3N8) virus has not acquired the ability of sustained transmission among humans. Therefore, the risk at the national, regional and international level of disease spread is assessed as low. However, further sporadic human cases can be expected as long as the virus continues to be detected in poultry populations. Additional information from human and animal investigations and studies is needed to better assess the current risk posed to public health.

The risk assessment will be reviewed in case further epidemiological or virological information indicates possible human-to-human transmission.

Prevention: Countries should raise public awareness to avoid contact with high-risk environments such as live animal markets/farms and live poultry or surfaces that might be contaminated by poultry or bird feces.

Personal protective measures include:

• Regular handwashing with proper drying of the hands
• Good respiratory hygiene – covering mouth and nose when coughing or sneezing, using tissues and disposing of them correctly
• Early self-isolation of those feeling unwell, feverish, and having other symptoms of influenza
• Avoiding close contact with sick people
• Avoiding touching one’s eyes, nose, or mouth
• Respiratory protection when at-risk environment

Appropriate infection prevention and control measures in health care settings should always be applied. Health care workers performing aerosol-generating procedures should use airborne precautions. Standard contact and droplet precautions and appropriate personal protective equipment (PPE) should be available during epidemics.

Travelers to countries and people living in countries with known outbreaks of avian influenza should, if possible, avoid poultry farms, contact with animals in live poultry markets, entering areas where poultry may be slaughtered, and contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Good food safety and hygiene practices should be followed. Travelers returning from affected regions should report to local health services if respiratory symptoms zoonotic influenza virus infection.

Surveillance: Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virological, epidemiological, and clinical changes associated with circulating influenza viruses that may affect human (or animal) health and timely virus and information sharing for risk assessment. A thorough investigation of every human infection and timely virus sharing with a WHO Collaborating Centre for reference and research on influenza and genetic and antigenic characterization is essential.

International Health Regulations: All human infections caused by a new subtype of influenza virus are notifiable under the International Health Regulations (IHR, 2005). A novel influenza A virus is considered to have the potential to cause a pandemic, and Member State Parties are required to immediately notify WHO of any laboratory-confirmed case of a human infection caused by such an influenza A virus. This event does not change the current WHO recommendations on public health measures and influenza surveillance.

International travel or trade: WHO does not recommend any travel and/or trade restrictions based on the currently available information.

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