Public Health

Bird flu news today: Avian flu symptoms in humans, CDC H5N1 milk warning and avian influenza vaccine


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What is the cause of bird flu? How does bird flu spread to humans? Is bird flu contagious? What are the symptoms of avian flu in humans? Is milk safe to drink?

Our guest is Jay Butler, MD, deputy director for infectious diseases at the CDC. AMA Chief Experience Officer Todd Unger hosts.


  • Jay Butler, MD, deputy director for infectious diseases, CDC

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Unger: Hello and welcome to the AMA Update video and podcast. Today, we're getting an update on the ongoing H5N1 bird flu outbreak from the Centers for Disease Control and Prevention. Our guest today is Dr. Jay Butler, deputy director for infectious diseases at the CDC in Anchorage, Alaska. I'm Todd Unger, AMA's chief experience officer in Chicago. Dr. Butler, thanks so much for taking time to talk with us today.

Dr. Butler: Well, thank you very much for giving me the opportunity to speak with you today.

Unger: Well, for those that follow the AMA Update, they know that we've been keeping a close eye on bird flu these past few months, and physicians and patients still have a lot of questions, as the virus continues to spread. Dr. Butler, can you start by giving us an update on the current status of the outbreak?

Dr. Butler: Well, as of June 24, H5N1 influenza has been detected in dairy cows in 120 premises in 12 different states. To date, three human cases have been detected in the U.S., all occurring in individuals who had exposure to cows that were in infected herds. The first case was in early April, in Texas, and then two cases were identified in late May, in Michigan. All three infections were relatively mild. The first two cases manifest only as conjunctivitis. The third case involved some burning, watery eyes, but also some mild respiratory symptoms, such as sore throat, runny nose and cough. All three individuals were treated with neuraminidase inhibitors, recovered and there were no instances where there was evidence of person-to-person spread.

Unger: Well, I think a lot of what you just said will help answer the question I'm about to ask, and that's the question about the risk level to the public right now. I think, so far, the CDC has repeatedly said that the risk to the public is low, but why don't you walk us through why that is, who's at risk and what could cause that risk level to increase?

Dr. Butler: So, CDC currently assesses the risk to human health for the general public from H5N1 influenza to be low. However, people with close, prolonged or unprotected exposure to infected birds or other animals, including now, livestock, or to environments contaminated by infected birds or other animals, have a greater risk of infection. So, for example, occupations that we would include that are in a higher risk category include dairy workers, slaughterhouse workers, milk processing facility employees, poultry farm workers, veterinarians and veterinary assistants.

Now, there's a few things that we're watching for very closely that would change the risk assessment for the public. First of all, if we identified multiple simultaneous instances of influenza H5N1 spreading from birds, cattle or other animals to people or certain genetic changes in circulating viruses, that could raise the alarm that could indicate that the virus is adapting and may be able to spread more easily among people. If limited, non-sustained person-to-person spread with this virus were to occur, that would also raise the public health threat level, because it would mean that the virus is adapting to spread among people. And finally, sustained person-to-person spread, which would be the hallmark for a pandemic, would certainly be a major concern and lead to sounding an alarm.

Unger: Absolutely. And, of course, that's why the CDC has been closely monitoring the outbreak and working hard with state and local partners to contain it. Dr. Butler, what are some of the efforts underway right now?

Dr. Butler: Yeah, so, there's four main ways that CDC is responding to the current situation with H5N1 influenza. First, we're supporting public health, as well as agricultural agencies, at the state, local and even tribal levels, to be able to basically have a One Health approach, as much, as possible, recognizing that animal health can influence human health and vice versa. Second, protecting human health and safety. We're supporting strategies that protect dairy and other agricultural workers who may be at higher risk than the general population. This includes making recommendations on use of personal protective equipment when working with infected herds.

As we learn more about the virus, these recommendations may change, but these are available on the CDC website. And also supporting states in monitoring people who have exposure to cows, birds or other domestic or wild animals that are infected or potentially infected with H5N1.

Third, understanding the risk to people from this virus. Again, this is a relatively new virus. We want to be able to determine whether or not there is evidence of spread that we're not detecting. So we've continued our wintertime flu surveillance through the summertime, especially in areas that have infected cattle. Also, this enhanced strategy involves more testing during summer months of persons who become symptomatic with influenza, as well as wastewater monitoring as well.

The fourth area is assessing influenza A viruses for genetic changes that could indicate that the virus is adapting to humans. So far, there have been no major mutations in the hemagglutinin gene, which would suggest an adaptation to humans. Also, I'll just add, there's been no major changes that would suggest high levels of resistance to oseltamivir, or other neuraminidase-inhibiting drugs or other antiviral agents.

Unger: And let's hope it stays that way. Dr. Butler, with bird flu spreading so much among dairy cattle, a lot of patients have questions about the safety of the milk supply. What should physicians tell their patients?

Dr. Butler: Yeah, that's a great question, because, as many of the listeners may be aware, the highest concentration of virus from the cattle has actually been in the milk. So, based on the current evidence from FDA, it does appear that pasteurization makes milk safe to consume. An important message for both public health professionals and providers is to continue to support the consumption of pasteurized milk and dairy products made from pasteurized milk and avoiding raw milk. Health care providers should educate patients of the risk of consuming unpasteurized milk, particularly emphasizing that unpasteurized milk or related products can contain bacteria or viruses, including H5N1 influenza that can adversely impact human health.

Certainly, we have seen, in the past few years, outbreaks of campylobacter, salmonella, E. coli, staphylococcus. There's the ongoing risk of exposure, potentially, to brucellosis. So, there's many reasons to really stick with pasteurized milk. CDC continues to monitor routine food safety surveillance systems for any unusual activity. Thus far, there's been no indication of anything related to H5N1.

Unger: That's good news. A couple of questions from patients, number one, about symptoms of bird flu, and then we'll talk a little bit about the vaccine. Let's start with the symptoms first. What do patients need to know there?

Dr. Butler: First, it's important to emphasize that clinicians should consider the possibility of H5N1 influenza in persons showing signs or symptoms of conjunctivitis or acute respiratory illness and who have relevant exposure history. It's a little difficult to talk about spectrum of disease, given that, right now, we have an N of three. The first two cases manifest primarily as conjunctivitis. The third case had some eye symptoms, but also mild respiratory illness.

We do know that H5N1 more broadly can cause more severe illness, sometimes relatively mild, with a flu-like illness, with cough, body ache and fever. There's also the possibility of abdominal pain, and vomiting, and diarrhea. And the progression to lower respiratory tract disease is always of concern. While we've had no hospitalizations in the United States globally, what we've seen with H5N1 influenza have included clinical signs of hypoxemia and signs of pneumonia. Laboratory findings include leukopenia, lymphopenia and mild to moderate thrombocytopenia. Radiographic findings include patchy, interstitial lobar and/or diffuse infiltrates and opacities.

If a person is symptomatic with relative exposure, CDC recommends isolation and notification of your local health department or state health department as soon as possible. Any symptomatic person among those being monitored after exposure should be started on empiric oseltamivir as soon as possible, even before test results become available.

Unger: All right, so, thank you for that overview on the symptoms front. Let's talk now about vaccines. What do patients need to know about the vaccine, should this situation change?

Dr. Butler: Yeah, vaccines are always an important part of the public health toolbox to prevent or lessen severity of disease. Given where we are in this current situation, there's no immediate recommendation to start vaccination of the general public or specific at-risk populations. CDC and partners in the government, including ASPR, are actively planning for potential H5 vaccination if it should be needed, and that includes beginning to stockpile vaccine. ASPR has recently placed an order for fill and finish for several million doses of an H5 vaccine.

We're putting things into position, so that we can deploy vaccines quickly and efficiently. And I would encourage everyone to get the seasonal flu vaccine this fall, because the more we can control seasonal flu, I think the less diagnostic confusion we'll see, particularly among people with occupational exposure to animals that could potentially be infected with H5.

Unger: Dr. Butler, before we wrap up, is there anything else that you'd like physicians to know in regard to bird flu?

Dr. Butler: Well, I think it's important to monitor this situation. It's unusual and concerning for a couple of reasons. First of all, dairy cattle are a new mammalian host for H5 influenza. Second, the instances of transmission from dairy cattle to humans, are the first instances of mammal-to-human transmission. In the past, all transmission of H5 influenza to humans has been from birds.

And, finally, the clade of H5 virus that's spread from cattle emerged in late 2020, and subsequently spread globally in migratory fowl. The viral genome analysis suggests that this virus jumped to dairy cattle around the end of 2023. Thus, while there have only been three human cases associated with exposure to infected dairy herds, and each case has been mild, this is an evolving situation. The CDC and state health departments have information available on their websites, but the outbreak status and recommendations may change as we learn more. If we know nothing about influenza, it is predictably unpredictable. So, please stay in touch.

Unger: And we absolutely will. Dr. butler, thank you so much for joining us to provide this important information and update, and we appreciate everything that you and the CDC are doing to address the outbreak. If you found this discussion valuable, you can support more programming like it by becoming an AMA member at That wraps up today's episode and we'll be back soon with another AMA Update. Be sure to subscribe for new episodes and find all our videos and podcasts at Thanks for joining us. Please, take care.

Disclaimer: The viewpoints expressed in this video are those of the participants and/or do not necessarily reflect the views and policies of the AMA.

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