Key facts
- One case of severe zoonotic avian influenza A(H5) has been confirmed on 13 December in Louisiana, United States (US). The case was exposed to sick and dead birds in backyard flocks.
- The case has been hospitalized with severe symptoms. This marks the first instance of severe illness linked to the virus in the United States.
- Partial viral genome data of the H5N1 avian influenza virus that infected the patient in Louisiana suggests the virus is of the D1.1 genotype.
- On 18 December, the Governor of California declared a state of emergency in the State to further expand monitoring and build on the coordinated approach to contain and mitigate the spread of the H5N1.
- As of 17 December 2024, a total of 61 human cases of avian influenza A(H5) have been reported from seven states in the US during 2024, including the most recent case. Of these, 37 were individuals exposed to dairy cattle known or presumed to be infected with A(H5N1) and 21 were workers exposed to outbreaks of HPAI A(H5) at poultry farms. Two people had no known animal exposure and one case had exposure to to other animals such as backyard flocks, wild birds, or other mammals.
- On 6 December 2024, the US Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) announced the start of its National Milk Testing Strategy (NMTS).
- According to the United States Centers for Disease Control and Prevention (US CDC), the risk to the general population remains low, while people with exposure to infected poultry, cattle or other potentially infected domestic or wild animals have a higher risk of infection.
Overview
Update: On 17 December 2024, the US CDC reported one new severe human case of avian influenza A(H5) (CDC H5 Bird Flu Update). According to the Centers for Disease Control and Prevention (CDC), the newly reported case occurred in Louisiana and was confirmed on 13 December. The individual reported exposure to sick and dead birds in backyard flocks, and this is the first case in the US that has been linked to this exposure. The case has been hospitalized with severe symptoms. This marks the first instance of severe illness linked to the virus in the United States.
Partial viral genome data of the H5N1 avian influenza virus that infected the patient in Louisiana suggests the virus is of the D1.1 genotype, which is linked to other recent D1.1 strains found in wild birds and poultry across the United States, as well as in recent human cases in British Columbia, Canada, and Washington state. This H5N1 strain differs from the B3.13 genotype, which has been detected in dairy cows, isolated human cases in various US States, and some poultry outbreaks. Further genomic sequencing and efforts to isolate the virus from the Louisiana patient's clinical samples are currently underway at the CDC.
On 29 April 2024, CDC recommended against consuming raw milk contaminated with live A(H5N1) virus as a way to develop antibodies against A(H5N1) virus to protect against future disease. Consuming raw milk can lead to serious health risks, especially for certain vulnerable populations.
On 6 December 2024, the US Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) announced the start of its National Milk Testing Strategy (NMTS). In partnership with state veterinarians, USDA implemented a strategy to collect unpasteurised milk samples to better assess where H5N1 is present, with the goal to better inform biosecurity and containment measures, as well as to inform state-led efforts to reduce risk to farm workers who may be in contact with animals infected with H5N1.
On 12 December 2024, a study showing that influenza virus may remain infectious in refrigerated unpasteurised milk for up to 5 days. The experiment was performed with a strain of human influenza virus H1N1 PR8.
Background: In 2024 and as of 17 December 2024, 61 human cases of avian influenza A(H5N1) have been confirmed by the US CDC from seven states. Thirty-seven of the cases reported exposure to dairy cattle in the following states: California (33), Colorado (1), Michigan (2) and Texas (1). Twenty-one cases reported exposure to poultry in the following states: Colorado (9), Oregon (1) and Washington (11). In addition, two cases have been identified with unknown exposure: one in Missouri and one in California; one case have been identified with exposure to other animals such as backyard flocks, wild birds, or other mammals.
The US CDC’s current assessment of the human health risk of A(H5N1) to the general public in the US has not changed and continues to be considered low.
ECDC assessment
To date, there have been no confirmed human cases of influenza A(H5N1) infection and no reports of A(H5N1) infection in cattle in the EU/EEA. The genotype B3.13, identified in cattle and several of the human cases in the US, has not been detected in Europe.
ECDC has assessed the risk from the circulating HPAI A(H5N1) clade 2.3.4.4b viruses as low for the general population and low-to-moderate for those with activities that expose them to infected or dead animals or contaminated environments (e.g. occupational exposure to infected animals).
Actions
ECDC is monitoring the situation together with partner organisations in Europe and will continue to update its assessment of the risk for humans in the EU/EEA as new information becomes available.
In addition to enhanced surveillance, active monitoring and testing of exposed individuals is recommended for early detection of human cases and to assess the possibility of human-to-human transmission, according to relevant ECDC guidance documents (Testing and detection of zoonotic influenza virus infections in humans; Investigation protocol of human cases of avian influenza virus; Enhanced surveillance of severe avian influenza virus infections in hospital settings).
Raising awareness – including among all primary care workers of the need to enquire about animal exposure and symptoms compatible with avian influenza infections and testing of symptomatic people with a history of exposure, following a risk-based approach is important. It is also important to communicate on the epidemiological situation in order to not miss or delay diagnosis of potential human cases.
Given the uncertainties related to mammal-to-mammal transmission and depending on the epidemiological situation, a low threshold can be considered for testing individuals exposed to potentially infected mammals (e.g. symptomatic individuals with conjunctivitis or respiratory symptoms). Due to the higher risk of infection for individuals exposed to infected animals and contaminated environments, appropriate personal protective measures and other precautionary measures should always be taken to mitigate the risk.
ECDC relevant publications:
- Testing and detection of zoonotic influenza virus infections in humans in the EU/EEA, and occupational safety and health measures for those exposed at work
- Investigation protocol of human cases of avian influenza virus infections in the EU/EEA
- Surveillance and targeted testing for the early detection of zoonotic influenza in humans during the winter period in the EU/EEA
- Joint ECDC-EFSA Drivers for a pandemic due to avian influenza and options for One Health mitigation measures
ECDC is in contact with the US CDC for further information and is closely following any updates on the event. ECDC monitors avian influenza strains through its influenza surveillance programme and epidemic intelligence activities in collaboration with the European Food Safety Authority (EFSA) and the EU Reference Laboratory for Avian Influenza in order to identify significant changes in the virological characteristics and epidemiology of the virus. Together with EFSA and the EU Reference Laboratory for Avian Influenza, ECDC produces a quarterly updated report on the avian influenza situation.