On 22 May 2024, the International Health Regulations (IHR) National Focal Point (NFP) for India reported to WHO a case of human infection with avian influenza A(H9N2) virus detected in a child resident of West Bengal state in India. This is the second human infection of avian influenza A(H9N2) notified to WHO from India, with the first in 2019. The child has recovered and was discharged from hospital. 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. Most human cases of infection with avian influenza A(H9N2) viruses are exposed to the virus through contact with infected poultry or contaminated environments. Human infection tends to result in mild clinical illness. Based on available information, further sporadic human cases could occur as this virus is one of the most prevalent avian influenza viruses circulating in poultry in different regions. With the currently available evidence, WHO assesses the current public health risk to the general population posed by this virus as low. However, the risk assessment will be reviewed should further epidemiological or virological information become available.

Description of the situation

On 22 May 2024, WHO received a notification from the IHR NFP regarding a human case of avian influenza A(H9N2) virus infection in West Bengal state, India.

The patient is a 4-year-old child residing in West Bengal state. The case, previously diagnosed with hyperreactive airway disease, initially presented to the paediatrician with fever and abdominal pain on 26 January 2024. On 29 January, the patient developed seizures and was brought to the same paediatrician. On 1 February, the patient was admitted to the pediatric intensive care unit (ICU) of a local hospital due to the persistence of severe respiratory distress, recurrent high-grade fever and abdominal cramps. The patient was diagnosed with post-infectious bronchiolitis caused by viral pneumonia. On 2 February, the patient tested positive for influenza B and adenovirus at the Virus Research and Diagnostic Laboratory at the local government hospital. The patient was discharged from the hospital on 28 February 2024.

On 3 March, with a recurrence of severe respiratory distress, he was referred to another government hospital and was admitted to the pediatric ICU and intubated. On 5 March, a nasopharyngeal swab was sent to the Kolkata Virus Research and Diagnostic Laboratory and tested positive for influenza A (not sub-typed) and rhinovirus. The same sample was sent to the National Influenza Centre at the National Institute of Virology in Pune for subtyping. On 26 April, the sample was sub-typed as influenza A(H9N2) through a real-time polymerase chain reaction. On 1 May, the patient was discharged from the hospital with oxygen support. Information on the vaccination status and details of antiviral treatment were not available at the time of reporting.

The patient had exposure to poultry at home and in the surroundings. There were no known persons reporting symptoms of respiratory illness in the family, the neighbourhood, or among healthcare workers at health facilities attended by the case at the time of reporting.

This is the second human infection of avian influenza A(H9N2) virus infection notified to WHO from India, with the first in 2019. Further sporadic human cases could occur as this virus is one of the most prevalent avian influenza viruses circulating in poultry in different regions.

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 through indirect contact with 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 diseases ranging from mild upper respiratory tract infection to more severe diseases and can be fatal. Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported.

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.

Public health response

WHO is providing continued support to the Government of India through technical advice, updates on risk assessment and updating contingency plans- both in the human and animal sectors in line with the global guidance.

The Government of India has implemented the following coordination activities in response to the incident:

A team composed of a public health specialist, a paediatrician, and veterinary officials from the Animal Husbandry Department and Veterinary College, and the Government of West Bengal was constituted to investigate the occurrence of influenza-like illness (ILI) in local poultry.

Surveillance of ILI in humans was enhanced in the reporting district and in neighbouring areas.

The District Veterinary Department enhanced surveillance of animals.

The Animal Husbandry Department will share information regarding surveillance of avian influenza viruses (all subtypes under surveillance) in poultry, wild birds, etc., in the affected and adjoining areas with State Health authorities and at the central level with the Ministry of Health and Family Welfare, Government of India.

WHO continues to support the strengthening of country IHR core capacities, ensuring that Ministry of Health and Department of Animal Husbandry colleagues, along with partners, are kept informed about emerging global risks of avian influenza at the animal-human interface.

In accordance with the One Health Joint Plan of Action (OH JPA), WHO is actively working to enhance the One Health approach by building capacity for joint risk assessments. WHO is providing technical support to update country-specific avian/pandemic influenza contingency plans, as requested.

WHO risk assessment

Most human cases of infection with avian influenza A(H9N2) viruses are exposed to the virus through contact with infected poultry or contaminated environments. Human infection tends to result in mild clinical illness. However, globally, there have been some hospitalized cases and two fatal cases reported in the past. Given the continued detection of the virus in poultry populations, sporadic human cases can be expected.

No additional confirmed cases have been reported in the local area based on joint investigations.

Currently, available epidemiological and virological evidence suggests that this virus has not acquired the ability to be sustained in transmission among humans. Thus, the likelihood of human-to-human spread is low. However, the risk assessment will be reviewed should further epidemiological or virological information become available.

International travellers from affected regions may present with infections either during their travels or after arrival in other countries. Even 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.

WHO advice

This case does not change the current WHO recommendations on public health measures and influenza surveillance at the human-animal and environmental interface. A thorough investigation of every human infection is essential.

The public should avoid unprotected contact with live poultry, high-risk environments such as live animal markets or farms, and surfaces that might be contaminated by poultry droppings.

Infection prevention and control (IPC) measures should be applied including performing hand hygiene frequently either by washing with soap and water or using alcohol hand rub solutions ensuring that the hands are visibly clean, in addition to environmental cleaning and disinfection.

WHO advice on implementing early infection control and prevention measures to prevent the nosocomial spread of the disease (that is, spread originating in a health care setting) include;

Raise awareness among healthcare workers regarding suspected cases.

Implement a screening and triaging (patient categorization) system in hospitals.

Implement standard and droplet precautions, and airborne precautions (N95/FFP2/FFP3), when aerosol-generating procedures are being carried out on suspected cases. Monitor healthcare workers for fever and influenza-like illness.

Provide personal protective equipment and appropriate training in its use.

All human infections caused by a new subtype of influenza virus are notifiable under the IHR (2005). 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 of pandemic potential (IVPP).

WHO advises against applying any travel or trade restrictions based on the current information available on this event. WHO does not recommend any specific measures for travellers.

About WHO

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