11 April 2023 

DISEASE OUTBREAK NEWS

Avian Influenza A(H3N8) - China

Situation at a glance

On 27 March 2023, 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 is the third reported case of human infection with an avian influenza A(H3N8) virus; all three cases have been reported from China.

Epidemiological investigation and close contact tracing have been carried out. There have been no other cases found among close contacts of the infected individual.

Based on available information, it appears that this virus does not have the ability to spread easily from person to person, and therefore the risk of it spreading among humans at the national, regional, and international levels is considered to be low. However, due to the constantly evolving nature of influenza viruses, WHO stresses the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses which may affect human (or animal) health. 

Description of the situation

On 27 March 2023, 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 patient was a 56-year-old female from Guangdong province with an onset of illness on 22 February 2023. She was hospitalized for severe pneumonia on 3 March 2023 and subsequently died on 16 March 2023.

The case was detected through the severe acute respiratory infection (SARI) surveillance system. The patient had multiple underlying conditions. She had a history of exposure to live poultry before the onset of the disease, and a history of wild bird presence around her home. No close contacts of the case developed an infection or symptoms of illness at the time of reporting.

Environmental samples were collected from the patient's residence and the wet market where the patient spent time before the onset of illness. The results of testing showed that the samples collected from the wet market were positive for influenza A(H3).

Epidemiology of the disease

Zoonotic influenza infections in humans may be asymptomatic or may cause disease. Depending on factors related to the specific virus and the infected host, disease can range from conjunctivitis or mild flu-like symptoms to severe acute respiratory disease or even death. Gastrointestinal or neurological symptoms have been reported but these are rare.

Human cases of infection with avian influenza viruses are usually the result of direct or indirect exposure to infected live or dead poultry or contaminated environments.

Public health response

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

• Enhanced monitoring and disinfection in the surrounding environment of the patient’s residence and suspected exposure areas;
• Public risk communication activities to improve public awareness and adoption of self-protection measures.

WHO risk assessment

Avian influenza A(H3N8) viruses are commonly detected globally in animals. Influenza A(H3N8) viruses are some of the most commonly found subtypes in birds, causing little to no sign of disease in either domestic poultry or wild birds. Cross-species transmission of A(H3N8) avian influenza viruses has been reported for various mammal species, including being endemic in dogs and horses.

This is the third reported human infection with A(H3N8) from China. Two previous cases were reported in April and May 2022. One of the previous cases developed a critical illness, while the other had a mild illness. Both cases likely acquired infection from direct or indirect exposure to infected poultry. So far, no additional cases linked with this case, nor the previous cases, have been reported. According to reports from health officials, the preliminary epidemiological investigation into this event suggests that exposure to a live poultry market may have been the cause of infection. However, it is still unclear what the exact source of this infection is and how this virus is related to other avian influenza A(H3N8) viruses that are circulating in animals. To better understand the current risk to public health, more information is needed from both human and animal investigation.

The transmission of avian influenza viruses from birds to humans is usually sporadic and happens in a specific context: most human infections with avian influenza viruses that have been reported previously were due to exposure to infected poultry or contaminated environments. Since avian influenza viruses continue to be detected in poultry populations, further sporadic human cases are expected in the future.

The available epidemiological and virological information suggests that avian influenza A(H3N8) viruses do not have the capacity for sustained transmission among humans. Therefore, the current assessment is that the likelihood of human-to-human spread is low. However, due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses which may affect human (or animal) health. 

WHO advice

To minimize the risk of infection, countries should increase public awareness of the importance of avoiding contact with high-risk environments such as live animal markets/farms, live poultry, or surfaces that may be contaminated by poultry or bird faeces. It is recommended to maintain good hand hygiene by frequently washing hands or using alcohol-based hand sanitizer and wearing respiratory protection when in a risky environment.

Given the observed extent and frequency of avian influenza cases in wild birds and some wild mammals, the public should avoid contact with animals that are sick or dead from unknown causes and should report the occurrence to the authorities.

Travellers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal faeces or other body fluids. Travellers should also wash their hands often with soap and water and follow good food safety and good food hygiene practices.

WHO advises against the application of travel or trade restrictions based on the information available at this time.

Influenza viruses are constantly evolving and large outbreaks occur among animal populations, which is why WHO stresses the importance of global surveillance to detect any changes in virology, epidemiology, and clinical patterns associated with emerging or circulating influenza viruses, which may pose a threat to human or animal health. Collaboration between the animal and human health sectors is essential. As the extent of influenza viruses circulation in animals is not clear, epidemiologic and virologic surveillance and the follow-up of suspected human cases should continue systematically. Timely sharing of information is critical for risk assessment.

The variety of zoonotic influenza viruses that have led to human infections is worrying and demands increased surveillance in both animal and human populations, as well as a comprehensive examination of each zoonotic infection, and planning for pandemics. To prevent a viral mutation that could make human-to-human transmission easier, poultry workers have been recommended to receive seasonal influenza vaccination.

If a human infection with a novel influenza virus that has pandemic potential, such as avian influenza, is confirmed or suspected, even before receiving confirmatory laboratory results,  contact tracing should be immediately initiated. A thorough epidemiological investigation should be conducted, including a history of travel and exposure to animals . The investigation should also involve early identification of unusual clusters of respiratory disease that could indicate person-to-person transmission of the novel virus. Clinical samples collected from the time and place that the case occurred should be tested, and then sent to a WHO Collaborating Centre for further characterization.

Close analysis of the epidemiological situation, further characterization of the most recent viruses found in humans and poultry, and serological investigations, are critical to assess risk and to adjust risk management measures in a timely manner.

Under the International Health Regulations (IHR 2005), States Parties are required to immediately notify WHO of any laboratory-confirmed case of human infection caused by a new subtype of influenza virus. Investigation, virus sharing, and genetic and antigenic characterization of every human infection are essential.

This event does not change the current recommendations from WHO for public health measures and surveillance of influenza.

Further information

• Influenza A Virus (H3N8): https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/influenza-a-virus-h3n8
• Transmission of Avian Influenza A Viruses Between Animals and People: https://www.cdc.gov/flu/avianflu/virus-transmission.htm
• Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005): https://www.who.int/publications/m/item/case-definitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)
• Guangdong Province Centre for Disease Control and Prevention, Press Release. 27 March 2023. http://cdcp.gd.gov.cn/ywdt/jkyw/content/post_4140571.html
• Joint FAO/OIE/WHO Preliminary Risk Assessment Associated with Avian Influenza A(H3N8) Virus. 18 May 2022. https://www.who.int/publications/m/item/joint-fao-oie-who-preliminary-risk-assessment-associated-with-avian-influenza-a(h3n8)-virus

Citable reference: World Health Organization (11 April 2023). Disease Outbreak News; Avian Influenza A (H3N8) – China. Available at https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON456

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