A child in California has become the first in the United States to test positive for bird flu infection, authorities said Friday, as health officials offered checks and preventive treatment to exposed contacts at the child`s day-care center.

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 centers 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.

Official statements emphasized that in the rare instances of bird flu transmission between individuals, the spread has been confined to a small number of close contacts.

Isolated and infrequent human cases of bird flu, with unclear sources of exposure or infection, are anticipated. They have occurred both historically and during the ongoing outbreak, which public health officials began monitoring in 2022.

"Including this most recent case, 55 human cases of H5 bird flu have now been reported in the United States during 2024, with 29 in California," said the CDC.

The CDC continues to estimate the risk for the general public is low -- albeit higher for those working directly with livestock animals including birds, dairy cattle and more.

A multistate outbreak of the flu -- technically the Highly Pathogenic Avian Influenza, or H5N1 bird flu -- was first reported in March in dairy cows.

The rising frequency and diversity of mammalian infections in recent years have heightened concerns about the virus`s adaptability and its potential for cross-species transmission.