A human case of H5N1 avian influenza, also known as bird flu, has been confirmed in a Stanislaus County resident who had contact with infected dairy cattle.
According to the Stanislaus County Public Health Department, the affected individual had mild symptoms and was treated with antiviral medications.
As of Friday, there were 66 confirmed human cases of bird flu nationwide. California has the most human cases at 37, followed by Washington (11) and Colorado (10). Of those infected, 40 were exposed by dairy herds, 23 by poultry farms and culling operations, two from an unknown source and one from another animal exposure.
In November, the Centers for Disease Control and Prevention confirmed that a child from Alameda County in the Bay Area tested positive for avian influenza. The child had no known contact with an infected animal, but public health experts were investigating a possible exposure to wild birds. In October, a person who came into contact with cattle at a dairy farm was Merced County‘s first confirmed human case of bird flu infection this year.
Officials are monitoring bird flu in wild birds, poultry and dairy herds. As of Dec. 23, there have been 50 states with outbreaks in poultry and 16 states with outbreaks in dairy cows. As of Wednesday, over 127 million poultry were infected and 891 dairy herds.
Bird flu is caused by strains of the flu virus that primarily infect birds and can spread quickly among them. They are novel influenza viruses, which differ from the seasonal flu virus strains that commonly circulate among humans. Bird flu can sometimes infect other animals and humans. A strain of bird flu, H5N1, is currently widespread in wild birds worldwide and is causing outbreaks in dairy cows and commercial poultry operations in the U.S. H5N1 bird flu was first detected in California dairy cows in August 2024.
Unlike the seasonal flu and other respiratory viruses like COVID-19, there is no evidence currently of person-to-person spread of the H5N1 bird flu virus. Instead, nearly all US cases of H5N1 bird flu are linked to direct and close contact with infected animals. The CDC and the CDPH report that the risk to the general public is very low at this time. People interacting with infected animals are at higher risk of getting bird flu. Wearing proper PPE helps prevent infection. Public health has been actively working alongside industry partners to distribute PPE to farmworkers.
Cows infected with bird flu can shed the virus in their milk. Pasteurized milk and dairy products continue to be safe to consume because pasteurization kills the H5N1 virus and other harmful bacteria and viruses.
“While the risk to the general population remains low, we want to ensure that those working with infected animals take proper precautions by using PPE,” said Stanislaus County Public Health Officer Dr. Thea Papasozomenos. “Exposed workers who have symptoms can reach out to Public Health if they need assistance getting evaluated and tested.”
People exposed to infected animals should monitor for the following symptoms for 10 days after their last exposure: eye redness (conjunctivitis), cough, sore throat, runny or stuffy nose, diarrhea, vomiting, muscle or body aches, headaches, fatigue, trouble breathing, and fever. If they start to feel sick, they should immediately isolate, notify Public Health, and work with Public Health and healthcare providers to get timely testing and treatment. Exposed workers with symptoms can notify Stanislaus County Public Health at 209-558-7535 or CDNurse@schsa.org.
Public Health recommends that all residents, especially workers at risk for exposure to bird flu, receive a seasonal flu vaccine. While the vaccine will not protect against bird flu, it can significantly decrease the likelihood of at-risk workers being infected with both viruses at the same time and reduce the chance of severe illness from seasonal flu.
