Avian Influenza A (H5N1) Outbreak - Australia - Prevention is better than cure

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7 June 2024

Situation at a glance

On 22 May 2024, the World Health Organization (WHO) was notified of a laboratory-confirmed case of human infection with avian influenza A(H5N1) virus (clade 2.3.2.1a) by the International Health Regulations (IHR) National Focal Point (NFP) of Australia. This is the first confirmed human infection caused by avian influenza A(H5N1) virus detected and reported by Australia. Although the source of exposure to the virus in this case is currently unknown, the exposure likely occurred in India, where the case had travelled, and where this clade of A(H5N1) viruses has been detected in birds in the past. According to the IHR (2005), a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact and must be notified to the WHO. Based on available information, WHO assesses the current risk to the general population posed by this virus as low.

Description of the situation

On 17 May 2024, the WHO Collaborating Centre (WHO CC) for Reference and Research on Influenza in Australia notified the NFP of Australia of a suspected case of human A(H5N1) avian influenza (HPAI) in Melbourne, Victoria.

The state Victorian Department of Health confirmed this case on 18 May 2024. Under Article 44, the NFP of Australia advised the NFP of India of the confirmed case on 21 May 2024. Under Article 8, the IHR NFP of Australia notified WHO of the case on 22 May 2024.

The case is a 2.5-year-old-female child with no underlying conditions. She had a history of travel to Kolkata, India from 12 to 29 February 2024. She returned to Australia on 1 March 2024.

Upon returning to Australia, the child presented at a hospital in Victoria on 2 March 2024, where she received medical care and was admitted on the same day. On 4 March, the patient was transferred to the intensive care unit at a referral hospital in Melbourne, Victoria, due to worsening symptoms, for a period of one week. The patient was discharged from hospital after a 2.5-week admission. The case is now reported to be clinically well.

The Victorian Department of Health reported on 23 May 2024 that the family advised that the child started to feel unwell on 25 February 2024, with loss of appetite, irritability and fever, and was taken to a doctor on the evening of 28 February 2024 in India. She was febrile, coughing and vomiting and was given paracetamol. It was not reported to an Australian airport biosecurity officer that the child was unwell when she arrived in Australia on 1 March 2024.

Additional information provided by the family indicates that the case did not travel outside of Kolkata, India, and did not have any known exposure to sick persons or animals while in India. It is understood that no close family contacts of the case in Australia or India developed symptoms, as of 22 May 2024.

A nasopharyngeal swab and endotracheal aspirate taken on 6 and 7 March respectively tested positive for influenza A at the referral hospital. The samples were sent to the WHO CC for further characterisation on 3 April as part of a batch, as there was insufficient knowledge from the referring practitioners at the hospital to connect the case to the H5N1 virus. Virus genetic sequence obtained from the samples confirmed the subtype A(H5N1) and indicated that the haemagglutinin (HA) gene belonged to clade 2.3.2.1a, which circulates in South-East Asia and has been detected in previous human infections and in poultry.

Epidemiology

Animal influenza viruses normally circulate in animals but can also infect humans. Infections in humans have primarily been acquired through direct contact with infected animals or contaminated environments. Depending on the original host, influenza A viruses can be classified as avian influenza, swine influenza, or other types of animal influenza viruses.

Avian influenza virus infections in humans may cause disease ranging from mild upper respiratory tract infection to more severe disease and can be fatal. Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported. There have also been several detections of A(H5N1) virus in asymptomatic persons who had exposure to infected birds.

Laboratory tests are required to diagnose human infection with influenza. WHO periodically updates technical guidance protocols for the detection of zoonotic influenza using molecular methods, e.g., RT-PCR. Evidence suggests that some antiviral drugs, notably neuraminidase inhibitors (oseltamivir, zanamivir), can reduce the duration of viral replication and improve prospects of survival in some cases.

From 2003 to 22 May 2024, 891 cases of human infections with avian influenza A(H5N1), including 463 deaths, have been reported to WHO from 24 countries. Almost all of these cases have been linked to close contact with infected live or dead birds, or contaminated environments.

India has reported detections of avian influenza A(H5N1) in domestic birds in 2024 to the World Organisation for Animal Health (WOAH). As the virus continues to circulate in poultry, the potential for further sporadic human cases remains. This is the first human infection with avian influenza A(H5N1) reported in Australia. In this case, the exposure likely occurred in India where this clade of A(H5N1) viruses has been detected in birds in the past, although the likely source of exposure to the virus is currently unknown.

Public health response

Australia

The Australian Government Department of Health and Aged Care convened a Monitoring and Investigation Team (MIT), with the first meeting held on 20 May 2024. Currently the MIT is meeting weekly, to assess any ongoing risk of the overall highly pathogenic avian influenza situation in Australia associated with the confirmed case of H5N1 in Victoria and the current international HPAI outbreaks. The frequency of the MIT meetings will be reassessed, as required.
The National Incident Centre of the Australian Government, Department of Health and Aged Care, has been activated to coordinate the response to the event.
The IHR NFP of India was notified on 21 May 2024.
On 22 May 2024, the Chief Health Officer of Victoria issued a health advisory on their website, informing of a recently reported human case of avian influenza in Victoria.
On 23 May 2024, the Head of the interim Australian Centre for Disease Control issued a media release about Australia’s first human case of avian influenza A(H5N1) in Victoria. The interim CDC’s website was updated and included public health advice about avian influenza. This included the importance for people who work on a poultry farm or factory, or travelling overseas to countries with avian influenza outbreaks, to get a seasonal influenza vaccination each year which can help prevent avian influenza from mixing with other influenza viruses which may lead to new mutated viruses thus becoming a greater threat to people.

India

On receipt of information from IHR NFP Australia, the Ministry of Health and Family Welfare, Government of India, initiated an epidemiological investigation with participation of all relevant sectors.

WHO risk assessment

This is the first human infection with an avian influenza A(H5N1) virus reported by Australia. Most human cases of infection with avian influenza viruses reported to date have been due to exposure to infected poultry or contaminated environments. Currently, the likely source of exposure to the virus in the case remains unknown but likely occurred in India where the patient travelled before onset of illness.

Human infection can cause severe disease and has a high mortality rate. These A(H5N1) influenza viruses, belonging to different genetic groups, do not easily infect humans, and human-to-human transmission thus far appears unusual. As the virus continues to circulate in poultry, particularly in rural areas, the potential for further sporadic human cases remains.

Currently, available epidemiological and virological evidence suggests that A(H5) viruses have not acquired the ability of sustained transmission among humans, thus, the likelihood of human-to-human spread is low.

Based on available information, WHO assesses the current risk to the general population posed by this virus as low. The risk assessment will be reviewed if additional virological and epidemiological information becomes available.

WHO advice

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

The public should avoid contact with high-risk environments such as live animal markets/farms and live poultry, or surfaces that might be contaminated by poultry droppings. Additionally, it is recommended to maintain good hand hygiene with frequent washing or the use of alcohol-based hand sanitizer.

The general public and at-risk individuals should immediately report instances of sick or unexpected animal deaths to veterinary authorities. Consumption of poultry that are sick or have died unexpectedly should be avoided.

Any person who has had exposure to potentially infected animals or contaminated environments and who feels unwell should seek health care promptly, inform their healthcare provider of their possible exposure, wear a face mask and limit contact with others. For more information, please visit the updated guidance here.

Close analysis of the epidemiological situation, further characterization of the most recent influenza A(H5N1) viruses in both human and animal populations, and serological investigations are critical to assess associated risks to public health and promptly adjust risk management measures.

There are no specific vaccines for influenza A(H5N1) in humans. However, candidate vaccines have been developed for pandemic preparedness in some countries. WHO continues to update the list of zoonotic influenza candidate vaccine viruses (CVV), which are reviewed and updated twice a year at the WHO consultation on influenza virus vaccine composition.

WHO advises against implementing travel or trade restrictions based on the current information available on this event. WHO does not advise special traveller screening at points of entry or other restrictions due to the current situation of influenza viruses at the human-animal interface.

State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by a new subtype of influenza virus. Evidence of illness is not required for this notification.