WASHINGTON: A child in California has become the first in the United States to test positive for bird flu infection, authorities said on Friday (Nov 22), as health officials offered checks and preventive treatment to exposed contacts at the child's day care centre.

The child, from Alameda County in the San Francisco Bay area, had mild symptoms and was said to be recovering at home following treatment with flu antivirals, according to the US Centers for Disease Control and Prevention (CDC) and the California Department of Public Health (CDPH).

As a precaution, close family members of the child were tested, with all results coming back negative.

Local officials have also contacted caregivers and families at the day care facility, where the child showed mild symptoms before testing positive.

The initial test detected low levels of bird flu virus, suggesting the child was likely not infectious at the time of testing. A follow-up test four days later returned negative.

In the United States, day care centres typically cater to children from six weeks to five years old.

"It's natural for people to be concerned, and 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," said CDPH director Tomas Aragon.

"No human-to-human spread of bird flu has been documented in any country for more than 15 years," he added.