A child in California tested positive for bird flu. Here’s why this case is different

An Alameda County child with mild upper respiratory symptoms tested positive for bird flu, state public health officials announced today. The potential infection is the first known case in California that does not appear to have originated from contact with infected cattle.

State health officials are waiting for the Centers for Disease Control and Prevention to confirm the test result.

Public health investigators suspect the infection may have originated from wild birds, which are the main carriers of bird flu, according to a statement from the California Department of Public Health. The agency did not disclose information describing the child’s interactions with wildlife.

The child displayed mild respiratory symptoms and tested positive for multiple viruses, according to Austin Wingate, a spokesperson for the Alameda County health department.

Doctors did not initially suspect bird flu. Officials detected it through routine influenza subtyping, Wingate said. Family members tested negative for bird flu, but they had other viruses.

Officials are working to notify and test close contacts of the child, which include individuals at a daycare the child attended.

“We want to reinforce for parents, caregivers and families that based on the information and data we have, we don’t think the child was infectious – and no human-to-human spread of bird flu has been documented in any country for more than 15 years,” said state Public Health Officer Dr. Tomás Aragón said in a statement.

Aragón emphasized the risk to the general public remains low. People can become infected through close contact with infected animals, according to the CDC. Dairy and poultry workers and people who work with wildlife face the greatest risk of contracting the virus.

Some infectious disease experts are concerned about what this case could signal about the wider bird flu outbreak sweeping the country, which started in 2022.

“We’re seeing the numbers go up, the number of infected farms, the number of farm workers, we now have this child. All of these signs to me suggest that things are going in the wrong direction, not the right direction,” said Sam Scarpino, an epidemiologist with Northeastern University in Boston who is not involved in the California disease investigation.

Cases spreading in Central Valley dairies

The case comes as California grapples with the country’s largest bird flu outbreak among cattle and farmworkers. There are 26 confirmed human cases of bird flu primarily in the Central Valley where the virus has swept through 335 herds, according to state health and agriculture officials. Workers in the dairy industry have contracted the virus through close contact with infected cows.

The state health department has distributed more than 3 million pieces of personal protective equipment to farmworkers. It has also secured 5,000 doses of the seasonal flu vaccine for farmworkers from the CDC.

The federal government has a small stockpile of bird flu vaccines, but they have not been distributed. Instead, health officials encourage people to get vaccinated for influenza, COVID-19 and respiratory syncytial virus to help prevent co-infections like the child had.

“We want to make sure in general that we promote people getting up to date on vaccines and protecting themselves from seasonal illness, from seasonal flu,” said Dr. Erica Pan, the state’s top epidemiologist, in a previous interview with CalMatters.

Scarpino said California has done a good job of testing farmworkers compared to other states where sick cattle have infected humans, contributing to its relatively high number of confirmed cases, but surveillance efforts across the board need to be increased.

As seasonal flu rates increase, it will become harder for public health laboratories to detect rare viruses, such as H5N1, the bird flu, Scarpino said.

Bird flu present in California sewage

The bird flu virus has appeared in 17 wastewater systems in California, according to the Centers for Disease Control and Prevention. Positive detections appear primarily in Northern California including in Alameda, San Francisco, Sonoma, Contra Costa and Sacramento. Wastewater surveillance cannot determine the source of the virus, but infections among wild waterfowl can contribute to its presence.

Maurice Pitesky, a researcher at UC Davis who studies bird flu in waterfowl, said it’s rare for the virus to jump from birds to humans, but it has happened before. The virus is endemic among wild birds, Pitesky said, and has also been detected in other mammals in California, including bobcats, skunks and mountain lions.

“As the virus further evolves within a mammalian host — whether it’s dairy cows, or felines, or all the species that it has affected — it will continue to adapt,” Pitesky said. “As it adapts more and more it has more potential to cause even more problems.”