This case represents the second reported human infection with avian influenza A(H5) in Mexico, and the first confirmed case of influenza A(H5N1) in the country. The patient was a child who died from respiratory complications.
Colorized transmission electron micrograph of avian influenza A H5N1 virus particles (yellow), grown in Madin-Darby Canine Kidney (MDCK) epithelial cells. Microscopy by CDC; repositioned and recolored by NIAID.
Image credit: CDC and NIAID
Earlier this month, Mexico notified the World Health Organization (WHO) of the country’s first laboratory-confirmed human infection with an avian influenza A(H5N1) virus in the country. The International Health Regulations (IHR) National Focal Point (NFP) reported it and stated the case was in the state of Durango in a child under the age of 10 years who tested positive for H5N1 at the Instituto de Diagnóstico y Referencia Epidemiológicos. The child did not have any underlying medical conditions, had not received seasonal influenza vaccination, and had no history of travel.
The child’s symptoms began on March 7, with fever, malaise, and vomiting. On March 13, the child was admitted to a hospital due to respiratory failure and antiviral treatment was initiated the next day. The child was transferred to a tertiary care hospital on March 16, and the child died on April 8 due to respiratory complications.
A nasopharyngeal swab was collected on March 18, and the sample was processed by real-time polymerase chain reaction (RT-PCR). The result was influenza A, non-subtypable. The sample was sent to the Centro de Investigación Biomédica del Noroeste (CIBIN), IMSS Monterrey, where the result was confirmed as influenza A, non-subtypeable, along with simultaneous detection of parainfluenza 3 virus. On March 31, the sample was forwarded to the Laboratorio Central de Epidemiología, where it was molecularly identified as influenza A(H5). On April 1, the sample was received by InDRE, where the positive result for influenza A(H5N1) was confirmed by RT-PCR. The sample was further characterized as avian influenza A(H5N1) clade 2344b genotype D11.
Officials say the source of infection remains under investigation. During contact tracing, 91 individuals were identified, including 21 household contacts, 60 healthcare workers, and 10 individuals from a childcare center. Pharyngeal and nasopharyngeal swab samples collected from 49 contacts tested negative for H5N1. To date, no further cases of human infection linked to this case have been identified. This case represents the second reported human infection with avian influenza A(H5) in Mexico, and the first confirmed case of infection with an influenza A(H5N1) virus in the country. In response to this medical event, local and national health authorities have implemented a range of measures to monitor, prevent, and control the situation. There have been reports of H5N1 outbreaks in birds in Durango, although the exact source of infection in this case remains under investigation.
Mexico has reported a confirmed human case of avian influenza A(H5N1) in a child with no known underlying conditions or exposure to influenza vaccination.
The child experienced severe respiratory illness leading to death despite receiving antiviral treatment. The illness progressed rapidly culminating in respiratory failure and death.
Extensive contact tracing and testing were conducted, but no further linked cases of H5N1 have been identified so far.
Check out our Spring 2025 issue cover story titled H5N1: The Outbreak the US Got Bored With.
In the US, The Centers for Disease Control and Prevention (CDC) recently reported there have 70 confirmed and probable human cases of H5N1 since the outbreak began in 2024 in the United States.2
The majority of these cases have been linked to exposure through commercial agricultural settings, with 41 individuals exposed through infected dairy herds and 24 associated with poultry farms and culling operations. Two additional cases were connected to other animal exposures, including backyard flocks and wild birds, and 3 remain of unknown origin.2
As in Mexico, there has been 1 death in the US, which was recorded in Louisiana back in January in a person who was older and was reported to have underlying medical conditions.3 The patient contracted H5N1 after exposure to a combination of a non-commercial backyard flock and wild birds.3 This individual had contracted H5N1 with a different genotype, D11. Previous cases of H5N1 contained the B313 genotype in farm workers exposed to infected cattle and poultry and caused milder symptoms and no hospitalizations.3
