U.S. health authorities confirmed a case of avian influenza in a California child on Friday—the first such instance reported in a U.S. minor.

The Centers for Disease Control and Prevention (CDC) reported that the child experienced mild symptoms, received antiviral treatment, and is recovering. Only the child’s residence in Alameda County, California (including Oakland), and daycare attendance have been disclosed.

This infection brings the total number of reported U.S. bird flu cases this year to 55, with 29 in California alone, according to the CDC.

One exception was an adult in Missouri without farm employment or known contact with infected animals. The source of their infection remains unknown; health officials found no evidence of human-to-human transmission.

Canadian officials also recently reported a British Columbia teenager hospitalized with avian influenza.

The H5N1 avian influenza strain has been widespread among wild birds, poultry, and other animals in the U.S. for several years.

Its spread to U.S. dairy cattle began in March. California has become the epicenter of this outbreak, with 402 infected herds identified since August—65% of the 616 herds confirmed in 15 states.

Officials are investigating the child’s infection source. California health officials previously suggested possible exposure to wild birds.

There is no evidence of the child transmitting the virus to others.

While household members reported similar symptoms, their bird flu tests were negative. The child and household members also tested positive for other common respiratory illnesses, officials noted.