Situation Overview
On May 23, 2024, the Mexico International Health Regulations (IHR) National Focal Point (NFP) reported a confirmed fatal case of human infection with avian influenza A(H5N2) virus to PAHO/WHO. This case, detected in a resident of the State of Mexico hospitalized in Mexico City, is the first laboratory-confirmed human case of A(H5N2) globally and the first avian H5 virus infection reported in Mexico. The source of the virus exposure is still unknown, though A(H5N2) has been identified in poultry in Mexico. Based on current data, WHO assesses the risk to the general population as low.
Detailed Case Information
The patient, a 59-year-old resident of the State of Mexico, was hospitalized in Mexico City. The patient had multiple underlying medical conditions and had been bedridden for three weeks before symptoms appeared. On April 17, the patient developed fever, shortness of breath, diarrhea, nausea, and general malaise. After seeking medical attention on April 24, the patient was admitted to the National Institute of Respiratory Diseases (INER) and died the same day due to complications.
Diagnostic Process
Initial testing at INER on April 24 using RT-PCR revealed a non-subtypeable influenza A virus. Subsequent sequencing on May 8 confirmed the virus as influenza A(H5N2). Further analysis by the Institute of Epidemiological Diagnosis and Reference (InDRE) on May 22 confirmed these findings.
Epidemiological Investigation
Health authorities conducted an epidemiological investigation, identifying 17 contacts at the hospital where the patient died. Only one contact exhibited mild symptoms, and tests for influenza and SARS-CoV-2 were negative. Additionally, twelve contacts near the patient’s residence tested negative for influenza and SARS-CoV-2. A connection between this human case and recent poultry outbreaks of A(H5N2) in Michoacán and the State of Mexico has not been established.
Understanding Avian Influenza
Avian influenza viruses primarily circulate in animals but can infect humans through direct contact with infected animals or contaminated environments. Human infections can range from mild respiratory symptoms to severe and fatal conditions. Laboratory testing, such as RT-PCR, is necessary for diagnosis, with WHO providing updated protocols for detecting zoonotic influenza.
Public Health Response Strategie: National Measures
Mexican health authorities have implemented several measures:
- Conducting epidemiological investigations of the case and contacts.
- Monitoring healthcare workers who had contact with the patient.
- Surveillance of influenza-like illnesses in nearby municipalities.
- Analyzing trends in respiratory infections and conjunctivitis.
- Identifying transmission chains and risk factors.
- Training on national preparedness and response guidelines for zoonotic influenza.
Public Health Response Strategie: International Support
- PAHO/WHO has taken the following actions:
- Strengthening surveillance at the human-animal interface.
- Enhancing diagnostic capacities for zoonotic diseases.
- Improving national capabilities for sample shipment to WHO centers.
- Conducting regular risk assessments for zoonotic virus transmissibility and severity.
- Updating guidelines on influenza surveillance and response.
- Reviewing experiences and lessons from countries affected by zoonotic influenza.
- Providing technical training for risk communication and clinical management of zoonotic influenza.
Risk Analysis
This is the first confirmed human infection with influenza A(H5N2) globally and the first such case in Mexico. Given the patient’s multiple underlying conditions and the ongoing investigation into the virus’s source, WHO assesses the current risk to the general population as low. While avian influenza viruses in poultry pose a risk for human infection, available evidence indicates that A(H5) viruses have not acquired the ability to sustain human-to-human transmission.
Public Health Advice
The current situation does not alter WHO’s recommendations on public health measures and influenza surveillance. Global surveillance is essential to detect and monitor changes in virological, epidemiological, and clinical aspects of emerging or circulating viruses. Enhanced surveillance in potentially exposed human populations is critical following human exposure to an influenza outbreak in animals. WHO continues to advise against special traveler screening at entry points or travel restrictions.
Travel Guidelines
Travelers to countries with known animal influenza outbreaks should avoid farms, live animal markets, and areas where animals are slaughtered. They should practice good hygiene, including frequent handwashing, and adhere to food safety guidelines. Infected individuals detected during travel are unlikely to cause further community-level spread due to the virus’s current transmission capabilities.
Reporting Obligations
All novel influenza A virus infections with pandemic potential must be immediately reported to WHO under the IHR, regardless of illness evidence. This enables timely risk assessment and response planning.
The recent human case of avian influenza A(H5N2) in Mexico highlights the importance of vigilant surveillance and robust public health responses to emerging zoonotic threats. Although the risk to the general population remains low, continued monitoring and preparedness are essential to mitigate potential impacts on public health.
Join TISHHA.
