California dairy workers infected with bird flu amid ongoing outbreak

Two dairy workers in California have tested positive for bird flu amid a multistate outbreak in cows.

The new positive tests bring the total number of human highly pathogenic avian influenza (H5N1) cases in the US to 16 this year and marked the first human cases in the state of California.

While the virus is widespread in birds and has caused outbreaks in poultry and cows, transmission from an infected person to a close contact is rare, according to the US Centers for Disease Control and Prevention (CDC).

Yet the agency heavily monitors human infections amid concerns that the virus could “change and gain the ability to spread easily between people”.

Experts are concerned that if the virus does acquire that ability, it could have pandemic potential.

“Current animal influenza viruses have not shown the capacity to transmit from person to person, but do pose a pandemic threat for the future,” the World Health Organization (WHO) said last month.

Risk to public remains ‘low’

The CDC confirmed the most recent bird flu cases on Thursday, but said it was “not unexpected” to detect the virus in people exposed to infected animals. The health agency added that the risk to the general public remained low.

“At this time, there is no known link or contact between the first and second confirmed cases in California, suggesting these are separate instances of animal-to-human spread of the virus,” the CDC said.

Symptoms of bird flu in humans include eye redness and mild flu-like symptoms such as a fever, cough, runny nose, and muscle aches.

The US outbreak of bird flu in dairy cows was first reported in March 2024, marking the first time it was detected in cows. There are now more than 250 dairy herds that have been infected in 14 US states.

The CDC recommends that people working with dairy cows or other animals that could be infected with H5N1 wear personal protective equipment. They also recommend not preparing or eating raw milk or cheese.

Bird flu has been reported in wild and domestic birds in 11 European countries but it has not been reported in mammals between June and September 2024, according to the European Centres for Disease Prevention and Control (ECDC).

The agency said the risk of infection from the currently circulating clade in Europe “remains low for the general public”.