Understanding the low risk of bird flu as outbreaks are recorded in the US
Key Takeaways
Outbreaks of bird flu have been detected in commercial turkey flocks in South Dakota and Utah.
Bird flu is currently considered a low public health risk with no known human-to-human transmission.
The CDC and USDA are monitoring recently detected bird flu infections in mammals.
Highly Pathogenic Avian Influenza (HPAI), more commonly known as bird flu, is a consistent presence in the United States’ wild bird population. Last week, the US Department of Agriculture (USDA) reported that it had detected a case on a commercial poultry farm in Jerauld County, SD. This was the first time since April that bird flu has been detected in commercial poultry in 2023.
Bird flu was detected in a flock of 47,300 turkeys. Infected commercial flocks are culled to prevent the spread of the virus. If more cases are found, it could result in a reduced supply of poultry and eggs in the US market. The loss of over 58 million chickens, turkeys, and other birds to the virus since 2022 was a driving factor in the record-high consumer costs of turkey meat and eggs last year.[]
Data from the Centers for Disease Control and Prevention (CDC) shows that similar outbreaks occurred recently on commercial poultry farms in Sanpete, UT. These outbreaks were also found in flocks of commercial turkeys, one of which consisted of 7,600 turkeys and the other of 134,200 turkeys. On October 10, an additional outbreak was reported in a flock of 50,300 poultry birds in Glacier, MT, under the care of the World Organization for Animal Health.[]
Previously, outbreaks in the US since April 2023 had only been found in non-poultry birds, live bird markets, and wild birds. Many wild birds, such as ducks and geese, are migratory and can potentially spread the virus during their travels, leading to outbreaks. This can make it difficult to track the virus or to predict future outbreaks.
Human transmission
The CDC classifies bird flu as a low public health risk. The last known case of a human infection in the US was in April 2022.[]
“It has spread to humans through direct contact with infected birds or indirect contact, such as touching the saliva or feces of infected birds. However, it’s important to remember this is extremely rare,” Christopher Swan, MD, an internal medicine specialist and cardiologist practicing in California, explains. “It’s only happened a little over 800 times in the past two decades, and the last time it happened in the United States was in April 2022.”
The individual infected in the US in 2022 was working to cull a flock of infected birds presumed to have contracted bird flu. Their only reported symptom was fatigue, and they recovered after antiviral treatment.[]
Since the beginning of 2022, there have been 15 reported human cases worldwide. None of these cases resulted from human-to-human transmission. The CDC states that nearly all individuals who developed an infection had been recently exposed to an ill or deceased bird.[]
The most recently reported human infections occurred in the United Kingdom during the spring and summer of 2023, when four people contracted bird flu. All of these individuals were asymptomatic. In 2022, an additional asymptomatic case occurred in the UK, and two people in Spain contracted bird flu with no reported symptoms. There have been two human deaths caused by bird flu since 2022: one in China and one in Cambodia. Severe infections causing critical illness, but not fatality, were reported in Chile, Ecuador, and Vietnam.[]
Bird flu and mammals
There has been concern about the spread of bird flu to mammals in 2023. However, the CDC calls these infections “sporadic.” In the US, these infections don’t appear as large outbreaks but instead as single or small instances of animals infected in varied locations across the country. For instance, in late August and early September 2023, bird flu was identified in five harbor seals in Washington State. In June 2023, , the virus was detected in a single fox in Michigan.[][]
In Spain, a large bird flu outbreak occurred in farmed minks in October 2022. However, despite these cases, the CDC considers the transmission risk to humans very low. Almost no reported cases have been reported of humans contracting bird flu through contact with infected mammals. Current data from recent US infections and from larger outbreaks, such as the one in Spain, does not indicate that the bird flu virus has mutated in ways that might lead to easier bird-t0-human or mammal-to-human transmission.[][]
“Now, in 2023, we see that there has been H1N1 infecting a lot of mammal populations. However, it’s important that there has still been no documented evidence of human-to-human infection. If that changes, recommendations will change,” says Dr. Swan.
The CDC and USDA continually monitor outbreaks and will determine if the risk to the public escalates. At this time, because bird flu is so rare in humans and does not spread through human-to-human contact, there is no need for most people to be concerned about it and their health. As a precaution, the CDC recommends that some people, such as those working with poultry, work to minimize outbreaks in poultry or frequently encounter wild birds and take extra steps to protect themselves. Additionally, the CDC advises that everyone avoid direct contact with wild birds and domestic or commercial birds that appear sick or have died.[]