Current Situation: Bird Flu in Humans

Background

Avian influenza (bird flu) Type A viruses do not normally infect people, but rare cases of human infection have occurred with some avian influenza viruses. Illnesses in humans from avian influenza virus infections have ranged in severity from no symptoms or mild illness (e.g., eye infection, upper respiratory symptoms) to severe disease (e.g., pneumonia) that resulted in death. Human infections with avian influenza viruses have most often occurred after close or lengthy unprotected contact (i.e., not wearing gloves or respiratory protection or eye protection) with infected birds or places that sick birds or their saliva, mucous and feces have touched. Very rarely, human infections with avian influenza viruses have happened through an intermediary animal, including a cat and a cow.

Human infections with avian influenza viruses can happen when virus gets into a person's eyes, nose or mouth, or is inhaled. This can happen when virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has virus on it and then touches their mouth, eyes or nose. The spread of avian influenza viruses from one infected person to a close contact is very rare, and when it has happened, it has not led to continued spread among people. Six main hemagglutinin (HA) subtypes of avian influenza viruses have infected people to cause acute respiratory illness (H3, H5, H6, H7, H9, and H10 viruses). Among these, H5N1 and H7N9 viruses have caused the majority of infections in people. More information about bird flu in humans is available at Bird Flu Virus Infections in Humans.

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Current U.S. Bird Flu Situation in Humans

• Sporadic infections with highly pathogenic avian influenza A(H5N1) viruses in mammals have been reported in the United States, Canada, and other countries, but the risk to the general public from these viruses remains low.
• In late March 2024, a human case of influenza A(H5N1) virus infection was identified after exposure to dairy cows presumably infected with bird flu. In May 2024, CDC began reporting additional, sporadic human cases in people who had exposure to infected dairy cows. That latest human case counts are available at H5N1 Bird Flu: Current Situation Summary.
  
• Only four human infections with low pathogenic avian influenza (LPAI)* A(H7N2) viruses resulting in mild-to-moderate illness have ever been identified in the United States.

The Current Risk to the General Public is Low

• The detections of avian influenza A(H5) viruses in wild birds, poultry, some mammals, and in people in the United States do not change the risk to the general public's health, which CDC considers to be low. However, due to outbreaks in domestic commercial and backyard poultry flocks, and infections in wild birds and some mammals, some groups of people with job-related or recreational exposures to birds or other H5 virus-infected animals, are at greater risk of infection. People with job-related or recreational exposures to birds or infected mammals should take appropriate precautions to protect against bird flu.
• Due to widespread circulation of avian influenza A(H5N1) virus in wild birds and poultry and sporadic infections in mammals, additional sporadic human cases would not be surprising.
• Right now, the H5N1 bird flu situation remains primarily an animal health issue. However, CDC is watching this situation closely and taking routine preparedness and prevention measures in case this virus changes to pose a greater human health risk.
• Signals that could raise the public health risk include multiple, simultaneous reports of human infections with avian influenza A(H5N1) viruses following exposure to birds or other animals, or identification of spread from one infected person to another.
• No known person-to-person spread has occurred with the contemporary avian influenza A(H5N1) viruses that are currently circulating in birds in the United States and globally. In other countries, sporadic human cases of human infections with the avian influenza A(H5N1) viruses most common in birds globally have been reported since 2022 mostly following exposure to infected poultry. During past avian influenza A(H5N1) virus outbreaks that have occurred in poultry globally, human infections were rare. Globally since 2003, 23 countries have reported rare, sporadic human infections with avian influenza A(H5N1) viruses to the World Health Organization (WHO). Monthly case counts are available on the WHO website.
• The spread of avian influenza viruses from one infected person to a close contact has occurred rarely in other countries in the past, and when it has happened, it has been limited and not sustained, and did not spread beyond close contacts.

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Protect Yourself From H5N1 When Working With Farm Animals | (Spanish)

More Information About Contemporary Avian Influenza A(H5N1) Viruses

• USDA has publicly posted the genetic sequences of avian influenza A(H5N1) viruses found in U.S. wild birds and poultry. The viruses are from clade 2.3.4.4bA, which is the most common avian influenza A(H5N1) virus worldwide at this time. Comparing information about these contemporary viruses to previously circulating avian influenza A(H5N1) viruses helps inform the human health risk assessment.
• CDC has been comparing the properties of contemporary avian influenza A(H5N1) viruses to past avian influenza A(H5N1) viruses and has found that contemporary avian influenza A(H5N1) viruses detected in the United States during late 2021 and 2022 are different from earlier avian influenza A(H5N1) viruses.
• Illness in humans from all avian influenza virus infections has ranged in severity from no symptoms or mild illness to severe disease that resulted in death in other countries. Total case counts for all human infections with avian influenza A(H5N1) viruses reported since 1997 are available.
• Occasional sporadic human infections with avian influenza A(H5N1) viruses do not change the human risk assessment to the general public, which CDC considers to be low.

Additional Resources

• Health Alert Network (HAN) – 00506 | Highly Pathogenic Avian Influenza A(H5N1) Virus: Identification of Human Infection and Recommendations for Investigations and Response
• Highlights in the History of Avian Influenza (Bird Flu) Timeline – 2020-2024
• CDC and USDA have developed guidance for specific audiences with exposure to sick or dead birds, including the general public, hunters, poultry producers, poultry outbreak responders, and health care providers.
• CDC has developed interim for Highly Pathogenic Avian Influenza A(H5N1) Virus in Animals.
• A handout containing information and guidance for people exposed to birds with bird flu is available at What To Know About Bird Flu.
• More information about how to protect yourself against bird flu is available.
• More information is available from CDC spotlight articles.

Learn more about bird flu in people.

Learn more about past human infections with bird flu viruses.