Following further investigation and information sharing by national authorities in Mexico, this is an update to the Disease Outbreak News (DON) on human infection caused by avian influenza A(H5N2) published on 5 June 2024. Link(https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON520).
As was previously reported, on 23 May 2024, the Mexico International Health Regulations (IHR) National Focal Point (NFP) reported to PAHO/WHO a confirmed case of human infection with avian influenza A(H5N2) virus in a patient with underlying co-morbidities who subsequently died. This is the first laboratory-confirmed human case of infection with an influenza A(H5N2) virus reported globally and the first avian A(H5) virus infection in a person reported in Mexico. Although the source of exposure to the virus in this case is currently unknown, A(H5N2) viruses have been reported in poultry in Mexico. In their update, Mexican authorities informed WHO that a national group of experts determined on 6 June that the patient died due to complications related to his co-morbidities and that genetic analysis performed by the national authorities identified that this virus has a 99% similarity with the strain obtained during 2024 in birds in Texcoco State of Mexico. Based on available information, WHO’s risk assessment is unchanged: the current risk to the general population posed by this virus is low. The risk assessment will be reviewed should further epidemiological or virological information become available.
Description of the situation
As summarized in the previous DON, on 23 May 2024, the Mexico IHR NFP reported to PAHO/WHO a confirmed case of infection with avian influenza A(H5N2) virus detected in a 59-year-old resident of the State of Mexico who was hospitalized on 24 April 2024 in Mexico City. The case had no known history of exposure to poultry or other animals. He had multiple underlying medical conditions. His relatives reported that he had been bedridden for three weeks, for other reasons, prior to the onset of acute symptoms. On 22 May, sequencing of the sample by the national authorities confirmed the influenza subtype was A(H5N2). The genetic analysis by the national authorities identified that this virus has a 99% similarity with the low pathogenicity (in birds) avian influenza A/chicken/Texcoco, México/CPA-01654/2024 (H5N2) strain, obtained during 2024 from birds in Texcoco State of Mexico. The detailed H5N2 virus genetic sequence from the patient specimen has been uploaded to GISAID.
A national multidisciplinary group of experts was formed to investigate the cause of death. It included infectious disease specialists, pneumonologists, microbiologists and intensive care professionals. Upon review of the patient’s clinical history and records, the national multidisciplinary team concluded on 6 June that, although the patient had a laboratory-confirmed infection with avian influenza A(H5N2) virus, he died due to complications of his co-morbidities.
No further cases were reported during the epidemiological investigation. The 17 contacts identified and monitored at the hospital where the man died and 12 additional contacts near his residence, were tested and the results were negative for influenza viruses. Samples from these persons were taken a month after the acute disease onset in the patient with confirmed influenza A(H5N2) infection. The results of the serological samples are pending.
In March 2024, an outbreak of low pathogenicity avian influenza (LPAI) A(H5N2) was identified in poultry in Texcoco, State of Mexico, and a second outbreak of LPAI A(H5N2) in April in the municipality of Temascalapa in the same state (1).
Additionally, in March 2024, a high pathogenicity avian influenza A(H5N2) outbreak was detected in a backyard poultry farm in the state of Michoacán. A study describing the continuous circulation of low pathogenicity avian influenza H5N2 viruses in Mexico and spread to several other countries was published in 2022 (2), indicating that both LPAI and HPAI A(H5) subtypes were reported in avian species in Mexico recently and in past years.
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 mild to severe upper respiratory tract infections and influenza-associated deaths have been reported in persons with or without comorbidities. 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, e.g. RT-PCR. Evidence suggests that some antiviral drugs, notably neuraminidase inhibitors (oseltamivir, zanamivir), can reduce the duration of viral replication and improve survival prospects for some cases.
Public health response
ALocal and national health authorities report implementing the following public health measures:
Conducting an ongoing investigation into the source of infection.
Formed a multi-disciplinary group experts to determine the cause of death. It comprised of professionals from Secretaría de Salud: Comisión Coordinadora de Institutos Nacionales de Salud y Hospitales de Alta Especialidad (CCINSHAE) of the Centro Nacional de Programas Preventivos y Control de Enfermedades (CENAPRECE); Dirección General de Información en Salud (DGIS), Dirección General de Epidemiología (DGE-InDRE) and Dirección General de Promoción de la Salud (DGPS); Secretarías de la Defensa Nacional (SEDENA); Secretaría de Marina Armada de México (SEMAR); and Instituto Mexicano del Seguro Social.
Issued official press releases including updates of national investigations and actions with a multisectoral approach, as well as general information and recommendations for the population.
The below actions were previously reported
Epidemiological investigation of case and contacts.
Monitoring of health care workers with a history of contact with the patient.
Monitoring and surveillance of influenza-like respiratory illness (ILI) and severe acute respiratory illness (SARI) in neighbouring municipalities (within the same health region), in order to analyze the behaviour and trends of respiratory syndromes and viruses in the region.
Analysis of the trends of pneumonia and bronchopneumonia, acute respiratory infections, and conjunctivitis by the health services of Mexico City and the State of Mexico.
Identification of transmission chains and risk factors in the municipality where the case resided, the State of Mexico and surrounding areas.
Training on the National Guide for preparedness, prevention and response to an outbreak or zoonotic influenza event at the animal-human interface.
Communicated with animal and environmental health authorities to strengthen surveillance activities in poultry and wild birds near the case's residence and areas with a history of low pathogenic avian influenza A(H5N2) outbreaks.
PAHO/WHO implemented the following measures:
Strengthening routine and event surveillance on the human-animal interface with WHO Collaborating Centers and strategic partners.
Improvement of molecular diagnostic capacity for detection of zoonotic diseases through knowledge transfer, training and technical support with recent emphasis in avian influenza A(H5N1).
Strengthening national capacity for the prompt shipment of human and animal samples to WHO collaborating centers for additional characterization and/or vaccine composition analysis.
Regular risk assessment for transmissibility and severity for zoonotic viruses.
Update of guidelines on influenza surveillance and response at the human-animal interface.
Revision of experiences in response and lessons learned from countries that experienced zoonotic influenza outbreaks.
Technical strengthening of risk communication capacities for events at the human-animal interface.
Clinical management training on zoonotic influenza treatment, infection prevention and control (IPC), and reorganization of health services.
Animal carcass handling training, including IPC technical aspects.
PAHO published recommendations to strengthen intersectoral work in surveillance, early detection, and research at the human animal interface.
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