Avian influenza (HPAI) A(H5N1), commonly known as bird flu, has seen an increase in human cases in the United States recently, mainly among poultry and dairy workers. H5N1 has primarily circulated in the Midwest, and these cases are raising concerns about potential human transmission and broader public health implications. Understanding the current landscape of H5N1, including recent data and prevention strategies, is essential as health officials continue to monitor the situation.1
The California Department of Public Health (CDPH) announced today that a child from Alameda County has tested positive for a suspected H5N1 avian flu infection. The child, who displayed mild upper respiratory symptoms, has no known contact with infected animals. If confirmed, this would be the second case in North America involving a child with an undetermined source of infection. It would also be the second such case in the US this year, involving someone with no exposure to sick farm animals. This would also mark the 27th H5N1 case in California this year, and the first not linked to sick animals on dairy or poultry farms.2
The Alameda County child is recovering at home, and health officials are investigating the potential source of the infection. While the child had no known contact with infected animals, the investigation is focusing on possible exposure to wild birds, particularly as the H5N1 virus spreads along migratory bird routes. Alameda County does not have commercial dairy herds, and the child had attended daycare while symptomatic. Health officials have notified other contacts and provided preventive treatment as a precaution.2
The child’s initial test for H5N1 avian flu showed a low-level detection of the virus, suggesting the child was unlikely to be infectious. Follow-up tests conducted four days later came back negative, and further tests indicated the presence of other respiratory viruses, which may have been responsible for the child’s symptoms. Specimens have been sent to the CDC for final confirmation.2
On September 6th, the CDC confirmed a human case of H5N1 avian influenza in Missouri, marking the first instance in which the virus was transmitted to a person without a known exposure to sick or infected poultry or livestock. The patient, who had underlying medical conditions, was hospitalized, treated with antiviral medications, and has since recovered. This case stood out because, unlike previous cases, there was no direct connection to poultry or livestock, raising concerns about potential unknown sources of transmission.3 This case, along with the new case in California, is notable for standing apart from earlier H5N1 cases in 2024, all of which involved individuals with a history of exposure to sick or infected poultry.
