On 27 March 2023, the National Health Commission of the People’s Republic of China notified WHO of a confirmed case of human infection with avian influenza A( H3N8 ) virus. This is the third reported case of human infection with an avian influenza A(H3N8) virus; all three cases were reported from China. Epidemiological investigations and close contact tracing were carried out. No other cases were found among close contacts of the infected individual.
Based on the 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 nationally, regionally and internationally is considered low. However, due to the evolving nature of influenza viruses, WHO emphasizes the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that 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 a confirmed case of human infection with avian influenza A(H3N8) virus. The patient was a 56-year-old woman from Guangdong Province with an onset of illness on February 22, 2023. She was hospitalized with severe pneumonia on March 3, 2023, and later died on March 16, 2023 .
The case was detected through the Severe Acute Respiratory Infections Surveillance (SARI) system. The patient had multiple underlying conditions. He had a history of exposure to live poultry prior to the onset of the disease and a history of wildfowl around his home. No close contacts of the case have developed an infection or symptoms of illness at the time of reporting. Environmental samples were collected from the patient’s residence and from the wet market where the patient spent time before the onset of illness. Test results showed that samples collected from the wet market were positive for influenza A(H3).
Disease epidemiology:
Zoonotic influenza infections in humans may be asymptomatic or may cause disease. Depending on factors related to the specific virus and infected host, the disease can range from conjunctivitis or mild flu-like symptoms to severe acute respiratory illness or even death. Gastrointestinal or neurological symptoms have been reported, but these are rare. Human cases of avian influenza virus infection usually result from 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:
- Increased monitoring and disinfection in the environment surrounding the patient’s residence and areas of suspected exposure;
- Risk communication activities to the public to raise public awareness and adopt 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 encountered subtypes in birds, causing little or no signs of disease in both domestic poultry and wild birds. Species-to-species transmission of avian influenza A(H3N8) viruses has been reported for various mammalian species, including being endemic in dogs and horses.
This is the third human infection reported with A(H3N8) from China. Two previous cases were reported in April and May 2022. One of the previous cases developed critical illness, while the other had mild illness. Both cases likely became infected through direct or indirect exposure to infected poultry. No additional cases related to this case, nor to previous cases, have been reported so far. 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 the 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 circulating in animals.
Transmission of avian influenza viruses from birds to humans is usually sporadic and occurs in a specific context: most of the previously reported human infections with avian influenza viruses were due to exposure to infected poultry or to contaminated environments. As avian influenza viruses continue to be detected in poultry populations, additional sporadic human cases are expected in the future.
Available epidemiological and virological information suggests that avian influenza A(H3N8) viruses do not have the capacity for sustained transmission between humans. Therefore, the current assessment is that the probability of human-to-human spread is low. However, due to the evolving nature of influenza viruses, WHO continues to emphasize the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that may affect human (or animal) health.
WHO advice:
To minimize the risk of infection, countries should raise public awareness of the importance of avoiding contact with high-risk environments such as live animal markets/farms, live poultry orwhich may be contaminated with poultry or bird feces. It is recommended to maintain good hand hygiene by washing hands frequently or using alcohol-based hand sanitizers and wearing respiratory protection when in a hazardous environment. Given the observed extent and frequency of cases of avian influenza in wild birds and some wild mammals, the public should avoid contact with animals that are sick or have died of unknown causes and should report the event to the authorities. Travelers to countries with known animal flu outbreaks should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered or touching surfaces that appear to be contaminated with animal faeces or other bodily fluids. Travelers should also wash their hands frequently with soap and water and follow good food safety and 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 influenza viruses emerging or circulating, 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 virus circulation in animals is unclear, epidemiological and virological surveillance and follow-up of suspected human cases should continue systematically. Timely sharing of information is critical to risk assessment.
The variety of zoonotic influenza viruses that have led to human infections is concerning and requires increased surveillance in both animal and human populations, as well as a thorough examination of each zoonotic infection and pandemic planning. To prevent a viral mutation that could facilitate human-to-human transmission, poultry workers have been recommended to receive the seasonal flu vaccination.
If human infection with a new influenza virus that has pandemic potential, such as avian influenza, is confirmed or suspected, even before confirmatory laboratory results are received, contact tracing should be initiated immediately. A thorough epidemiological investigation should be conducted, including a history of travel and exposure to animals. Investigation should also involve early identification of unusual clusters of respiratory illnesses that could indicate person-to-person transmission of the new virus. Clinical specimens collected from the time and place of the incident should be tested and then sent to a WHO collaborating center for further characterisation.
A careful analysis of the epidemiological situation, further characterization of the most recent viruses found in humans and poultry and serological investigations are essential for risk assessment and timely adaptation of risk management measures. 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 any human infection are essential. This event does not change current WHO recommendations for public health measures and influenza surveillance.
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-whom-in-all-circumstances-under-the-ihr-(2005)
- Guangdong Province Center for Disease Control and Prevention, press release. March 27, 2023. http://cdcp.gd.gov.cn/ywdt/jkyw/content/post_4140571.html
- Preliminary joint FAO/OIE/WHO risk assessment of the risk associated with the avian influenza A(H3N8) virus. May 18, 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 (April 11, 2023). Disease Epidemic News; Avian influenza A (H3N8) – China. Available at https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON456
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