As bird flu continues to spread among poultry and dairy cows across the United States, health officials have confirmed the country's first "severe" human case of avian influenza (H5N1).
A person in Louisiana has been hospitalized with bird flu, which marks the state's first human case and the first instance of severe illness caused by the H5N1 virus in the U.S., the Centers for Disease Control and Prevention said. The patient had exposure to sick or dead birds in backyard flocks.
“The patient is experiencing severe respiratory illness related to H5N1 infection and is currently hospitalized in critical condition,” a spokeswoman for the Louisiana Health Department told NBC News.
Since April 2024, there have been 61 human cases of avian influenza A (H5) confirmed in the U.S. The majority are among people who had contact with infected cattle or poultry. The Louisiana patient is the first human case linked to a non-commercial backyard flock.
Bird flu is a disease caused by infection with avian influenza A viruses, which spread naturally among wild aquatic birds and circulate in poultry. Occasionally, bird flu viruses spread to mammals and, rarely, to humans.
“The current bird flu strain that we’re concerned with, H5N1, has been circulating around the world for quite some time,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, previously told TODAY.com.
Since 2022, H5 bird flu has been detected in commercial poultry and domestic flocks in the U.S. in 48 states. In 2024, H5N1 has caused an ongoing outbreak among dairy cows which has spread to 875 herds in 16 states, per the U.S. Department of Agriculture.
No person-to-person spread has been reported in the U.S. so far.
Based on available information, the CDC assesses the current risk to the public posed by bird flu to be “low.” However, the recent uptick in human cases has sounded the alarm among officials in the U.S. and abroad, who are monitoring bird flu viruses closely.
RELATED: Will bird flu lead to another pandemic in the US? Experts weigh in as concerns grow
Here's what to know about the spread of H5N1 bird flu in the U.S. and symptoms.
61 cases of human bird flu in the U.S. in 2024
Since the start of 2024, human H5N1 bird flu cases have been reported in the following states, according to the latest CDC data:
- California: 34
- Colorado: 10
- Louisiana: 1
- Michigan: 2
- Missouri: 1
- Oregon: 1
- Texas: 1
- Washington: 11
Of these cases, 37 individuals had exposure to infected cattle, 21 had exposure to poultry, one had exposure to non-commercial backyard flocks, and two cases had an “unknown exposure,” or no known contact with animals, per CDC data.
“The risk to members of the general public who do not have exposure to infected animals remains low,” the CDC said.
In most of the human H5N1 cases in the U.S., people have experienced mild symptoms. These include mild flu-like upper respiratory symptoms such as coughing and a runny nose, and eye redness and inflammation (conjunctivitis). No deaths have been reported in the U.S. so far.
Experts say it’s unlikely this specific strain of bird flu would lead to a pandemic because H5N1 does not transmit between humans efficiently, TODAY.com previously reported.
Where is bird flu spreading in the U.S.?
California has reported the largest share of human bird flu cases this year, 34. This includes the first case of H5N1 reported among a child in the U.S., the CDC said. The child, who had no known exposure to sick animals, experienced mild symptoms and recovered at home.
California has also declared a state of emergency over bird flu as the virus spreads among cows, according to the Governor's office.
Washington, which has the second-largest share of cases, reported 11 human H5N1 infections among workers at a poultry farm in October.
Colorado has reported 10 human cases of H5N1 in 2024, nine among poultry workers and one in a dairy worker. The workers experienced mild respiratory symptoms and conjunctivitis (pink eye), according to the Colorado Department of Public Health.
Louisiana has confirmed one human case of bird flu, linked to non-commercial (non-poultry) backyard bird flocks, the Louisiana Department of Health said on Dec. 19.
Oregon recorded its first human bird flu case in November, which was linked to an outbreak at a poultry operation, the CDC said.
In August, Missouri confirmed its first human H5N1 case in a person who was hospitalized for a respiratory illness. The patient, who had underlying medical conditions and was treated with antiviral flu medications at the hospital, has since recovered and had no known exposure to sick animals, the CDC said on Sept. 6.
Two farmworkers in Michigan tested positive for bird flu in May, and one dairy worker in Texas tested positive for H5N1 in April.
The human case in Texas was the first time this strain of H5N1 — referred to as highly pathogenic avian influenza A (HPAI) — had been detected in cows and the first instance of cow-to-human transmission, according to the CDC.
The highly pathogenic H5N1 strain causing the current U.S. outbreak is severe and often fatal in birds, but appears to be mild in cows and most humans.
Prior to 2024, the only human case of H5N1 reported in the U.S. was reported in a poultry worker in Colorado in April 2022.
Teenager hospitalized with bird flu in Canada
On Nov. 13, 2024, Canada reported its first human case of H5N1, in a teenager in British Columbia. The patient tested positive for H5N1 avian influenza after being hospitalized for acute respiratory distress in early November, NBC News previously reported.
The teenager was otherwise healthy and had no underlying conditions, British Columbia’s health officer, Dr. Bonnie Henry, said in a news conference. However, the teen’s deterioration was “quite rapid,” Henry said, and they remained in critical condition at the hospital by the end of November.
Fatal human bird flu case in Mexico
In May, authorities in Mexico confirmed a fatal human case of H5N2 bird flu. The patient was the first human to become infected with an avian H5 virus in Mexico and the first human case of H5N2 reported globally, per the World Health Organization.
The 59-year-old died in a hospital in Mexico City in April after developing a fever, shortness of breath, diarrhea, nausea and “general malaise,” per the WHO.
The patient reportedly had multiple underlying health conditions, but had no contact with sick animals and the source of exposure was unknown. However, H5N2 viruses have been detected in poultry in multiple states in Mexico, the WHO said.
What are the symptoms of bird flu?
Bird flu infections in humans can range in severity, experts note. Some people have no symptoms or only a mild flu-like illness, while others can develop severe disease requiring hospitalization, per the CDC.
“It can be a serious infection with a high mortality rate,” said Schaffner.
According to the CDC, reported signs and symptoms of bird flu include:
- Cough
- Runny nose
- Muscle aches
- Fever
- Headache
- Fatigue
- Shortness of breath
- Eye redness or inflammation (conjunctivitis)
- Diarrhea
- Nausea
- Vomiting
Bird flu in humans may look similar to seasonal influenza or upper respiratory infections. In severe cases, bird flu can lead to pneumonia or respiratory failure, TODAY.com previously reported.
Many of the human cases in the U.S. have reported conjunctivitis or pink eye, either as their only symptom or in addition to respiratory symptoms. Only one case so far has resulted in severe respiratory illness and complications requiring hospitalization.
An infection with bird flu viruses cannot be diagnosed by signs or symptoms alone, the CDC says. Laboratory testing is required.
How does bird flu transmit to humans?
Transmission of bird flu viruses to humans is rare. According to the WHO, since 2003, there have been approximately 903 human H5N1 cases in 24 countries. Most human cases have been caused by H7N9, highly pathogenic H5N1 or H5N6 viruses, per the CDC.
Avian influenza can spread from infected birds to humans in a few ways, per the CDC:
- Directly from an infected bird
- From environments contaminated with bird flu viruses
- Through an intermediate host, such as another animal
Infected birds can shed the virus in their saliva, nasal secretions, mucus and feces. People can become infected when the virus particles get into the mouth, nose, eyes or are inhaled, Schaffner said.
Humans typically become infected with bird flu viruses through close, unprotected contact with an infected bird.
When it comes to the dairy workers with conjunctivitis, the CDC noted in a press release that “it’s not known exactly how eye infections result from avian influenza exposures.”
“It may be from contamination of the eye(s), potentially with a splash of contaminated fluid, or touching the eye(s) with something contaminated with A(H5N1) virus, such as a hand. High levels of A(H5N1) virus have been found in unpasteurized milk from H5N1-infected cows," the CDC said.
Human-to-human transmission of bird flu viruses is very rare. The few cases that have been documented have occurred primarily through prolonged, unprotected contact between a symptomatic person and a family member or caregiver, per the CDC.
“The virus doesn’t have the (genetic) capacity to spread easily from person to person,” Schaffner said.
However, in an April press conference, the WHO's chief scientist of called the risk of the bird flu spreading to humans “an enormous concern,” and warned about the potential for the virus to acquire the ability to spread more efficiently between people. Scientists are closely monitoring bird flu viruses for any changes.
Preventing bird flu
There is no evidence that humans can get bird flu from chicken, eggs or beef that’s been properly prepared and cooked, and it is safe to drink pasteurized milk, experts say.
The national milk supply now must be tested for bird flu viruses, according to a new order issued by the USDA on Dec. 6.
The risk of getting bird flu is low, but the CDC recommends people:
- Avoid contact with wild birds
- Avoid contact with sick or dead birds
- Avoid visiting poultry farms
- When in contact with poultry, wear a mask and eye protection
- Wash hands after any contact with poultry
- Visit a doctor if you become sick after contact with birds
