Health officials on Friday confirmed bird flu in a California child — the first reported case in a U.S. minor.

The child had mild symptoms, was treated with antiviral medication, and is recovering, the U.S. Centers for Disease Control and Prevention (CDC) said in announcing the test results. State officials have said the child attends daycare and lives in Alameda County, which includes Oakland and surrounding communities, but released no other details.

The infection brings the reported number of U.S. bird flu cases this year to 55, including 29 in California, the CDC said. Most were farmworkers who tested positive with mild symptoms.

One exception was an adult in Missouri who did not work at a farm and had no known contact with an infected animal. It remains a mystery how that person was infected. 

Health officials have said there was no evidence of it spreading between people.

A British Columbia teen also was recently hospitalized with bird flu, Canadian officials have said.

H5N1 bird flu has been spreading widely in the U.S. among wild birds, poultry and other animals over the last few years.

It began spreading in U.S. dairy cattle in March. California has become the centre of that outbreak, with 402 infected herds detected there since August. That's 65 per cent of the 616 herds confirmed with the virus in 15 states.

Officials said they were investigating how the child was infected. California health officials previously said in a statement that they were looking into a "possible exposure to wild birds."

There is no evidence bird flu spread from the child to other people.

People in the child's household reported having similar symptoms but their test results were negative for bird flu. Health officials noted the child and the household members also tested positive for other common respiratory viruses.