Deleted CDC data points to possible H5N1 spread between cats and humans

A cat may have infected a teenager with H5N1 bird flu at a U.S. home, while a dairy worker might have infected a cat at different home, according to a data table that appears to have been mistakenly uploaded to a weekly report on the Centers for Disease Control and Prevention (CDC) website.

The table was apparently accidentally included on Thursday in an update about the California wildfires in the Morbidity and Mortality Weekly Report published by the CDC, according to The New York Times. It appeared briefly before being removed. The table contained data from two households where cats were found to be infected with H5N1 bird flu.

The table, obtained by both the NYT and The Washington Post, suggests that an infected cat may have transmitted Highly Pathogenic Avian Influenza (HPAI) H5N1 to a teenager and another cat in a U.S. household.

In Household 1, a teenager developed symptoms six days after the onset of illness in a cat, which may have also infected another cat in the same home. However, the adolescent tested negative for the virus when examined six days later after developing symptoms. Two other people in the household also tested negative and did not develop symptoms.

In Household 2, the data suggests that a dairy worker, who had symptoms of bird flu, may have transmitted the virus to a domestic cat, or the cat may have been exposed to the same source of infection.

Both cats from the two households tested positive for HPAI (A)H5N1 and died with signs or symptoms of the disease.

Data from the U.S. Department of Agriculture indicates that bird flu detections in domestic cats first began in Oregon in 2022. Since then, more than 15 states have reported H5N1 infections in at least 85 household cats, with the highest numbers recorded in California (17 cases) and South Dakota (12 cases).

The CDC has not officially confirmed a possible transmission link between cats and humans. The agency has been under an external communications pause for federal health agencies since January 21, following an order from the Trump administration, according to WaPo. The Thursday report was the first CDC release in over two weeks.

LINK: A list of all human cases of H5N1 bird flu since 2021

H5N1 clade 2.3.4.4b and its various genotypes have raised concerns due to their global spread and the increasing number of infections in mammals. However, human cases have so far only been confirmed from spillover events involving birds and dairy cattle.