A CHILD tested positive for H5N1 bird flu after experiencing conjunctivitis, health officials have confirmed.
The patient, from San Francisco, California, also had a fever and tested positive for flu and RSV.
Local officials are racing to determine how the child might have contracted bird flu, which scientists believe could soon evolve to spread more easily between humans.
This change, experts warn, could pave the way for a potential human pandemic.
"The clock is ticking for the virus to evolve to more easily infect and potentially transmit from human to human, which would be a concern," Professor Luis Martinez-Sobrido, from the Texas Biomedical Research Institute, warned in a separate release.
However, Dr Grant Colfax, from the San Francisco Department of Public Health, reassured the public, stating, "I want to assure everyone in our city that the risk to the general public is low.
"There is no current evidence that the virus can be transmitted between people."
This comes just weeks after California declared a state of emergency due to a bird flu outbreak affecting dairy cows and causing sporadic human cases.
So far, there are currently a total of 67 confirmed cases of bird flu in humans, according to the US Centers for Disease Control and Prevention (CDC).
It's one case more than last week, which could be the child.
The presumptive case tested positive for H5N1 at the SFDPH Public Health Laboratory, but confirmatory testing will be performed at the Centers for Disease Control and Prevention (CDC).
The majority (38) of the cases are coming from California, most of whom have picked up the virus after working directly with cows.
Other states with confirmed cases include Colorado (10), Michigan (2), Missouri (2), Oregon (1), Texas (1) and Washington (11), according to the Centers for Disease Control and Prevention.
Last month, a 65-year-old man in Louisiana became the first person ever to die of H5N1 bird flu in the US.
Nearly all of the cases detected so far have presented with mild symptoms, including conjunctivitis and sore throat.
This includes the child from San Fransisco, who was never admitted to hospital and has since made a full recovery.
However, the Louisiana patient contracted a different strain of the virus - one linked directly to birds, rather than the strain currently circulating among dairy cattle.
This bird-derived strain is believed to cause more severe illness.
The reason why the H5N1 strain circulating in dairy cattle, known as the B3.13 genotype, causes only mild illness in humans remains unclear.
Scientists believe it could be related to the way the virus spreads, with most cases linked to contact with milk from infected cows.
It's thought that inhaling the virus directly into the airways could lead to more severe illness.
A new study by Scripps Research in San Diego tested various genetic mutations on virus material from infected cattle.
Their tests revealed a mutated strain of H5N1 capable of binding to human upper respiratory cells.
This adaptation could make it easier for the virus to spread between people via coughing or sneezing, sparking fears it's evolving to infect humans more effectively.
Researchers recently found that H5N1 is just one mutation away from being able to transmit between humans - a change that could potentially trigger a global pandemic.
According to the UK Health Security Agency (UKHSA), the virus is highly unlikely to affect cattle in Britain and the risk to the public is low.
But an order has been placed for five million doses of a vaccine against the H5 family of viruses if bird flu begins to spread in humans.