The California Department of Public Health now has confirmed six cases of human bird flu, according to an announcement Friday morning.

This announcement of the latest two patients follows the confirmation of the state’s fourth case Thursday afternoon.

All six cases are in individuals in the Central Valley who had direct contact with infected dairy cows. Two cases originated from the same farm, where both people had “extensive exposure to infected dairy cattle,” according to a news release from the California Department of Public Health.

The fourth infected person is from the Central Valley and also had contact with infected dairy cows, according to a department news release sent Thursday.

The first four people who were reported as infected came into contact with infected animals at four separate farms. Authorities concluded that there was no known link between any of those confirmed cases, indicating that the disease spread directly from animal to human.

Authorities said they believe that the evidence continues to suggest the virus spreads only from animals to humans despite two cases at the same farm given “the amount of exposure to infected cows” both infected individuals had.

Federal scientists took samples from the first two people in the Central Valley infected with bird flu and concluded that there were no genetic changes to the virus that would suggest an increased ability to infect people or spread between people, according to the press release.

The California Department of Public Health has been notified of another potential bird flu case in the Central Valley, and a specimen has been sent to the Centers for Disease Control and Prevention for confirmation.

Those infected have shown mild symptoms, including eye redness or discharge, and none was hospitalized. The risk of contracting bird flu for the general public is low, but the Public Health Department is expecting more cases of bird flu among people who interact with infected dairy cows.

Bird flu, also known as avian influenza, is a viral infection that most commonly affects birds; it can affect wildlife and reduce the food supply. Humans can be infected, but it is rare for the virus to spread from person to person. The H5N1 virus is the most common cause of bird flu in humans. According to the Cleveland Clinic, the death rate for bird flu in humans is over 50%.

Some people with bird flu might suffer only mild or no symptoms, but many get severely ill. Symptoms include fever, fatigue, cough, muscle aches, sore throat, nausea and vomiting, diarrhea, stuffy or runny nose and shortness of breath, according to the Cleveland Clinic.

As of Thursday, the California Department of Food and Agriculture announced that 99 dairy herds in Central California were infected with bird flu. State public health officials recommended personal protective equipment for those who are working with animals or materials that may be infected with the bird flu virus, like face shields or safety goggles for eye protection, N95 masks and gloves.

According to the California Department of Food and Agriculture, this current nationwide outbreak of bird flu began in poultry in 2022. It first was detected in dairy cattle in March.