Bird flu: What to know about latest outbreaks after U.S. reports first severely infected person

A recent avian influenza outbreak among California dairy cows and the first known severe human case of H5N1 bird flu in the U.S. have reignited concerns online about the disease.

Some social media users pointed to the disease’s high fatality rate in humans and warned of an impending bird flu pandemic.

Meanwhile, other social media users claimed the bird flu outbreaks were staged. A Dec. 18 Instagram post said California Gov. Gavin Newsom declaring a state of emergency over the bird flu outbreak was part of "agenda to start another pandemic."

Another Instagram post referred to Newsom’s emergency declaration and said, "Y’all ready for the next hoax?"

Avian flu is a real disease, but U.S. public health experts say it poses a low risk to humans. There have been no cases of human-to-human spread of H5N1 bird flu.

Avian influenza is a naturally occurring disease among wild birds, including ducks and geese, that can also infect domesticated birds, such as chickens and turkeys. Highly pathogenic strains of bird flu can cause severe infection and high fatality in birds. Low pathogenic strains trigger mild infections, but can turn highly pathogenic.

Domesticated birds can contract avian flu through contact with infected birds or through contact with surfaces contaminated with the virus. Because avian flu spreads quickly and is untreatable in animals, infected flocks are culled to prevent further infection.

This colorized electron microscope image released by the National Institute of Allergy and Infectious Diseases on March 26, 2024, shows avian influenza A H5N1 virus particles (yellow), grown in Madin-Darby Canine Kidney (MDCK) epithelial cells (blue). (AP)

This strain of highly pathogenic avian influenza, H5N1, was discovered in U.S. wild birds in January 2022, the Centers for Disease Control and Prevention said. Soon after, the virus began causing outbreaks in commercial and backyard poultry flocks.

Since 2022, more than 128.8 million birds overall, in all 50 states, live on premises where H5N1 bird flu has been detected. Sporadic infections of other wild animals, including bears, foxes and skunks, have also been reported.

In March, bird flu was detected in dairy cows for the first time in the U.S. Since then, 16 states have reported bird flu outbreaks in dairy cows.

California has reported 266 new cases of avian flu in dairy cows over the past 30 days, the most of any state. Newsom said in a statement that his emergency proclamation is "a targeted action to ensure government agencies have the resources and flexibility they need to respond quickly to this outbreak."

Over the past 30 days, as of Dec. 19, the U.S. Agriculture Department’s Animal and Plant Health Inspection Service said avian flu affected more than 14.55 million birds in commercial and backyard flocks across 11 states. Once one bird in a flock is infected with the disease, the whole flock is considered affected because the disease is so contagious among poultry.

It’s unusual for people to contract avian flu, but rare cases have occurred globally for nearly three decades, the CDC said. Infections can happen when the bird flu virus gets into a person’s eyes, nose or mouth, or is inhaled.

The first bird flu outbreak among humans happened in 1997 in Hong Kong. About 20 people were infected there between 1997 and 2003, and seven people died from infection, the CDC said.

No human cases were reported elsewhere in the world until 2003, the CDC said. From 2003 to Nov. 1, 2024, the World Health Organization said, H5N1 bird flu has infected 939 humans across 24 countries, including the U.S.

The CDC reported Dec. 18 that 62 humans have been infected with bird flu in the U.S., with all but one of those cases occurring this year.

The first U.S. case was reported in 2022 when a prison inmate caught the disease while killing infected poultry on a Colorado farm as part of a prerelease program. The person’s only symptom was fatigue and he recovered.

On April 1, the second U.S. case of bird flu infection in a human was reported. The person, who had been exposed to infected cows in Texas, reported having eye redness.

Since April, 60 other people in the U.S. have contracted the disease, including one person recently hospitalized in Louisiana with the first severe case. This person had been exposed to sick and dead birds in a backyard flock, the CDC said.

Bird flu remains primarily an animal health issue and the risk to the general public remains low, the CDC said.

Social media posts that raised alarm about the avian flu’s fatality rate in humans — such as a Dec. 19 Threads post that said the disease has a "30-50% fatality rate" — are misleading.

Of the 959 people diagnosed with H5N1 avian flu worldwide since 1997, about 471, or 49%, have died, according to WHO and CDC data. But that number needs context. Most of the bird flu deaths were reported in Egypt and Indonesia before 2020, according to the WHO.

It’s possible that mild or asymptomatic cases of bird flu in humans are not being detected or reported as well in low- and middle-income countries, "so only those cases who are getting very sick are being picked up, along with their contacts — this is going to bias the case fatality data upwards, most likely," Claire Standley, an associate research professor at Georgetown University’s Center for Global Health Science and Security who specializes in zoonotic diseases, told PolitiFact in April. 

No deaths from bird flu infection have been reported in the U.S.

Bird flu fatality rates differ from country to country. The fatality rate in Egypt is about 33% and in Indonesia, it’s 84%. Egypt’s lower fatality rate may be because the infections were less severe, detected early and treated better, the European Centre for Disease Prevention and Control said.

Standley said disease severity depends on many factors, including a person’s previous exposure to the disease, underlying health conditions, age, access and quality of health care and exposure to the pathogen.

The federal government has bird flu vaccines in its stockpile, but they are not available for retail sale. The U.S. Food and Drug Administration must authorize vaccines before they can be used, and the FDA has not authorized bird flu vaccines.

The CDC said vaccine manufacturers could use candidate vaccine viruses — in this case, bird flu viruses prepared by public health officials — to produce a H5N1 avian flu vaccine, if one was needed in an emergency. The CDC said it routinely develops candidate vaccine viruses for bird flu viruses "with pandemic potential as part of pandemic preparedness activities."

In this image provided by the U.S. Department of Agriculture, a researcher performs a rapid antigen test on milk from a dairy cow inoculated against bird flu in a containment building at the National Animal Disease Center research facility in Ames, Iowa, on July 29, 2024. (AP)

The Agriculture Department said poultry and eggs that are properly prepared and cooked to an internal temperature of 165° Fahrenheit are safe to eat.

The chance of poultry affected by the avian flu entering the food supply is minuscule. The department’s Food Safety and Inspection Service personnel inspect poultry products intended for human consumption for signs of disease before the products enter the market.

The Agriculture Department and the Food and Drug Administration said the commercial milk supply remains safe because these products must be pasteurized before entering the market. Pasteurization heats dairy products to destroy any bacteria and viruses in them.

Also, dairies must send only milk from healthy animals into processing for human consumption. Milk from avian flu-infected animals is diverted or destroyed so that it stays out of the human food supply, the department said.

The FDA warns against consuming raw milk or unpasteurized dairy products because they can harbor dangerous microorganisms that can seriously threaten health.