US flu activity continues to decline across the country, according to the latest update from the US Centers for Disease Control and Prevention (CDC) today.

The weekly FluView report, which covers the week ending Jan 14, shows the percentage of outpatient visits for influenza-like respiratory illness dropped to 3%, down from 4% the previous week. In addition, only seven jurisdictions reported high flu activity, down from 20. No jurisdictions reported very high flu activity, compared with two the previous week. The CDC also noted that three regions were below their outpatient respiratory illness baselines for the first time since October 2022.

The percentage of respiratory specimens that tested positive for flu fell from 8.6% to 4.6%. Influenza A made up 97.3% of flu samples from clinical labs, and the H3N2 strain remains the dominant strain, accounting for 81.3% of subtyped specimens at public health laboratories.

Flu hospitalizations also continued to decline from their peak in week 48 (early December), when nearly 28,000 new influenza hospital admissions were reported. A total of 6,367 flu hospitalizations were reported for the week ending Jan 14.

Six more flu-associated pediatric deaths were reported, bringing the total number of pediatric flu deaths for the 2022-2023 flu season to 85. An additional pediatric death from week 27 of the 2021-22 season was also reported to the CDC, bringing the total number of pediatric deaths for that season to 45.

The CDC estimates there have been at least 25 million illnesses, 270,000 hospitalizations, and 17,000 deaths from flu so far this season.

Several countries have reported instances of H5N1 avian flu infections in mammals, but now Spanish researchers have reported the first known outbreak in farmed mink. They described their investigation yesterday in Eurosurveillance.

The outbreak began in early October 2022 at a farm housing nearly 52,000 mink in Galicia region in northwest Spain. Farm workers noted a sharp increase in deaths, and nasopharyngeal swabbing of the mink revealed H5N1 avian influenza. The mortality rate increased each week, spreading from hot spots to the rest of the barns, peaking toward the end of October.

The mink were housed in partially open barns and were fed raw fish, poultry byproducts sourced from the same region, and other items.

Potential public health implications

A more detailed genetic analysis of the H5N1 virus found that it belonged to the current clade circulating in wild birds and poultry on multiple continents and is most closely related to a strain found in seabirds across Europe.

The scientists found that the H5N1 virus has an uncommon mutation that was seen only once before in a European polecat and that it could have arisen on its own in the mink. They said the mutation in the PB2 gene may have public health implications, given that it is present in the avian-like PB2 gene of the 2009 H1N1 pandemic flu virus and has characteristics that enable recognition by human airway receptor cells.

The virus was involved in wild bird deaths in Galicia in the weeks leading up to the mink farm outbreak, and the birds could have introduced the virus to the farm, given that the barns were partially open. The researchers said, however, that more sequencing is needed to confirm the connection. They added that no avian flu outbreaks had been reported at poultry farms that supplied byproducts to the mink farm.

No related human infections were found at the farm. Spanish mink farm workers are required to wear masks because of the risks of SARS-CoV-2 in those setting. The authors said more studies are under way to look at virulence and transmissibility of the virus. Since mink have been suggested as a possible mixing vessel for respiratory viruses, the group emphasized that interventions are needed to prevent contact between mink and wild animals and to control transmission between farm works and mink.