Avian Influenza A (H5N1) - United States of America
Situation at a glance:
WHO was notified of a human case of avian influenza A (H5) in Colorado State in the United States of America on 29 April 2022. The case was involved in culling of poultry at a farm where influenza A (H5N1) virus was confirmed in the poultry. Avian influenza A (H5) was confirmed in the case on 27 April by the US Centers for Disease Control and Prevention and subtype N1 was confirmed subsequently by sequence analysis. The close contacts and people involved in culling of poultry have been identified, tested and are currently being followed up. Based on available information, WHO assesses the risk to the general population posed by this virus to be low and for occupationally exposed persons it is considered to be low-to-moderate.
Description of the case:
On 29 April 2022, the National IHR Focal Point of the United States of America notified WHO of a laboratory confirmed human case of avian influenza A(H5), in a male from Colorado State.
The case developed fatigue on 20 April, during participation in slaughtering poultry from 18 to 22 April, at a commercial poultry facility in Colorado where influenza A (H5N1) virus had been confirmed in the poultry.
Upon request of the organization providing personnel for culling of poultry at this facility, a respiratory sample was collected from the case on 20 April. The sample was received by the Colorado Department of Public Health and Environment Laboratory Services on 22 April and testing was completed on 25 April. Influenza A virus was detected by reverse transcriptase- polymerase chain reaction (RT-PCR). The sample was sent to the Influenza division of the United States Centers for Disease Control and Prevention (CDC) for further confirmation. Influenza A(H5) virus was confirmed by RT-PCR on 27 April and subtype N1 was subsequently confirmed by sequence analysis.
Public health response
On 20 April 2022, a total of nine samples from close contacts of the case and persons who participated in culling of poultry at the same facility were collected; all tested negative for influenza. Additional respiratory specimens were obtained on 28 April from the same nine contacts and tested negative for influenza.
Virus characterization including genetic analysis to compare the virus sequence obtained from the human sample to virus sequences obtained from the poultry outbreak and antigenic analysis to compare with existing candidate H5 vaccine viruses are ongoing.
The close contacts of the patient have been recommended to receive influenza antiviral prophylaxis. The investigation is ongoing to determine if there are additional close contacts.
All individuals who were exposed to poultry and involved in depopulation activities at this facility are being monitored for symptoms for 10 days following the last date of their last exposure and will be tested if symptomatic in accordance with the US CDC guidelines and US Department of Agriculture guidance. Close contacts of the index case are also being monitored.
WHO risk assessment
Since 2003 to 31 March 2022, a total of 864 cases and 456 deaths of influenza A(H5N1) human infection have been reported worldwide from 18 countries, however, this is the first reported case in the United States of America. The most recent case in humans prior to the current case, was reported in January 2022 in a case who had symptom onset in December 2021, from the United Kingdom of Great Britain and Northern Ireland.
Whenever avian influenza viruses are circulating in poultry, there is a risk for sporadic infection and small clusters of human cases due to exposure to infected poultry or contaminated environments. Therefore, sporadic human cases are not unexpected.
The virus has not been detected in humans beyond this single case in the United States of America. Public health measures from both the human and animal health agencies have been implemented. Based on available information, WHO assesses the risk to the general population posed by this virus to be low and for occupationally exposed persons it is considered to be low-to-moderate.
WHO advice
This case does not change the current WHO recommendations on public health measures and surveillance of influenza.
Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect and monitor virological, epidemiological and clinical changes associated with emerging or circulating influenza viruses that may affect human (or animal) health and timely virus sharing for risk assessment.
In the case of a confirmed or suspected human infection caused by a novel influenza virus with pandemic potential, including a variant virus, a comprehensive epidemiologic investigation (even while awaiting the confirmatory laboratory results) of history of exposure to animals, of travel, and contact tracing should be conducted. The epidemiologic investigation should include early identification of unusual respiratory events that could signal person-to-person transmission of the novel virus and clinical samples collected from the time and place that the case occurred should be tested and sent to a WHO Collaboration Center for further characterization.
When avian influenza viruses are circulating in an area, people involved in specific, high-risk tasks such as sampling sick birds, culling and disposing of infected birds, eggs, litters and cleaning of contaminated premises should be trained on the proper use of and provided with appropriate personal protective equipment (PPE). All persons involved in these tasks should be registered and monitored closely by local health authorities for seven days following the last day of contact with poultry or their environments.
Travelers 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 feces. Travelers should also wash their hands often with soap and water. Travelers should follow good food safety and good food hygiene practices. Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
All human infections caused by a novel influenza subtype are notifiable under the International Health Regulations (IHR) and State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic. Evidence of illness is not required for this report.
International travel or trade: WHO does not advise special traveler screening at points of entry or restrictions with regard to the current situation of influenza viruses at the human-animal interface.
Further information
- PAHO/WHO.
Influenza at the Human-Animal Interface: PAHO Recommendations to
Strengthen Intersectoral Work for Surveillance, Early Detection, and
Investigation, 9 July 2020.
- Current technical information including monthly risk assessments at the Human-Animal Interface.
- US CDC. General information about variant and influenza A viruses in swine
- Novel Influenza A Virus Infections Dashboard
- WHO. Influenza virus infections in humans October 2018.
- Case definitions for diseases requiring notification under the IHR (2005).
- Internal Health Regulations (2005).
- Manual for the laboratory diagnosis and virological surveillance of influenza (2011).
- Terms of Reference for National Influenza Centers of the Global Influenza Surveillance and Response System.
- Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases.
- World
Organization for Animal Health (OIE). H5N1 Highly Pathogenic Avian
Influenza in poultry and wild birds: Winter of 2021/2022 with focus on
mass mortality of wild birds in UK and Israel.
- WHO. Influenza at the human-animal interface.
- U.S. CDC. Case of Human Avian Influenza A(H5) Virus Reported.
- Intercontinental Movement of Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4 Virus to the United States, 2021.
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