Update: 6 dairy workers infected in California as bird flu outbreak spreads

Six people have contracted bird flu in California amid outbreaks in the state’s dairy industry, officials confirmed Friday.

On Thursday, officials had confirmed a fourth person was infected and were awaiting final lab results on two more possible cases.

As in prior confirmed cases, all six people worked in the state’s agricultural Central Valley and were in contact with infected dairy cattle, the U.S. Centers for Disease Control and Prevention said in an update Friday. All people identified with the infection in California have had mild symptoms including eye redness or discharge. None has been hospitalized.

California officials said the risk to the general public remains low, however, people who “interact with infected animals are at higher risk of getting bird flu.”

There are no known links between the six confirmed cases, which suggests there is widespread transmission among dairy herds and the infected cattle pose risks to people working near them.

One of the newly identified people who is infected worked on the same farm as a previously infected person, but the two people worked in different areas of the facility and were not in close contact, the CDC said.

In addition, California officials said Friday that a seventh person in the Central Valley may also be infected with bird flu. Officials are awaiting final lab results in that case from the CDC.

So far, officials have identified 20 people across the U.S. infected with bird flu this year. Nearly all of them worked with infected dairy or poultry livestock. However, one person infected in Missouri has no known source of transmission, according to state and federal officials.

Blood test results are pending for close contacts of the person in Missouri, who had been hospitalized with the virus. The contacts include several health workers who treated the person for bird flu. Some of those workers came down with mild respiratory symptoms, but state and federal officials from the CDC stressed there wasn’t evidence of human-to-human transmission, which would mark a shift in virus transmission.

On Friday, CDC officials said they had completed genetic sequencing of the bird flu virus taken from three people in California with the disease. Results show the viruses closely match the strain in infected dairy cows. There is no evidence of genetic changes to the virus that could increase the chance of contagion, spread between people or reduce the effectiveness of antiviral medications used to treat it. 

As of Friday, 100 dairy herds in central California have reported confirmed cases of bird flu in cattle, the CDC said. The increase in infected cows on California farms has significantly altered the number of herds nationally with the virus. Nearly 300 herds across 14 states have confirmed bird flu cases.

Health officials recommend workers wear personal protective equipment, including N95 respirators, goggles, face shields and gloves. 

The CDC is also ramping up its efforts to vaccinate livestock workers, who are at greater risk of contracting bird flu, against seasonal influenza. Seasonal flu vaccines do not provide protection against bird flu. However, officials fear that a cross-reaction of both influenza viruses in the body can cause bird flu to mutate to spread more easily or cause serious illness.

The federal government has also stockpiled emergency bird flu vaccines. Those vaccines have not been used yet.