Highly Pathogenic Avian Influenza A(H5N1) Virus: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations

Summary

The purpose of this guidance is to outline CDC's recommendations for preventing exposures to highly pathogenic avian influenza (HPAI) A(H5N1) viruses, infection prevention and control measures including the use of personal protective equipment, testing, antiviral treatment, patient investigations, monitoring of exposed persons (including persons exposed to sick or dead wild and domesticated animals and livestock with suspected or confirmed infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus), and antiviral chemoprophylaxis of exposed persons. These recommendations are based on available information and will be updated as needed when new information becomes available.

Background

Although human infections with HPAI A(H5N1) virus are rare, having unprotected exposure to any infected animal or to an environment in which infected birds or other infected animals are or have been present increases risk of infection. Therefore, people with work or recreational exposures to H5N1 virus-infected animals are at increased risk of infection and should follow recommended precautions.

The panzootic of HPAI A(H5N1) viruses in wild birds has resulted in outbreaks among commercial poultry and backyard bird flocks and has spread to infect wild terrestrial and marine mammals, as well as domesticated animals. Sporadic human infections with HPAI A(H5N1) virus have been reported in 23 countries since 1997 with a case fatality proportion of >50%, but only a small number of H5N1 cases have been reported in humans since 2022. Most human infections with H5N1 virus have occurred after unprotected exposures to sick or dead infected poultry. Since the spring of 2024, sporadic human infections have been reported in the United States. associated with poultry exposures or with dairy cattle exposures associated with the ongoing multi-state outbreaks of HPAI A(H5N1) virus among dairy cattle and poultry. There is no evidence of sustained human-to-human H5N1 virus transmission in any country, and limited, non-sustained human-to-human H5N1 virus transmission has not been reported worldwide since 2007.

Avian influenza A viruses infect the respiratory and gastrointestinal tracts of birds causing birds to shed the virus in their saliva, mucus, and feces. Influenza A viruses can also infect the respiratory tract of mammals and cause systemic infection in other organ tissues. Human infections with avian influenza A viruses can happen when enough virus gets into a person's eyes, nose, or mouth or is inhaled. People with close or prolonged unprotected contact with infected birds (e.g., sick/dead poultry) or other infected animals (e.g., dairy cows) or their contaminated environments are at greater risk of infection. Illnesses in people from HPAI A(H5N1) virus infections have ranged from mild (e.g., upper respiratory symptoms, conjunctivitis) to severe illness (e.g., pneumonia, multi-organ failure) that can result in death.

Since 2022, many different wild bird species have been reported with HPAI A(H5N1) virus infection, including terrestrial, seabird, shorebird, and migratory species. In the United States, HPAI A(H5N1) virus detections in wild birds have been reported in 50 states or territories, and outbreaks in commercial poultry or backyard bird flocks associated with high mortality have been reported in 48 states since February 2022.

A wide range of terrestrial and marine mammals have been reported with HPAI A(H5N1) virus infection in multiple countries, typically resulting in neurologic signs of disease and death. HPAI A(H5N1) virus infection has been reported in wild mammals such as foxes, bears, seals, and sea lions, and in domesticated animals, including pets such as cats and dogs, farmed mink and foxes, and livestock such as goats and dairy cows. In the United States, HPAI A(H5N1) virus detections in mammals have been reported in more than 20 states including detections in dairy cattle herds in 15 states as of November 2024.

At this time, CDC considers the human health risk to the U.S. public from HPAI A(H5N1) viruses to be low; however, people with close or prolonged, unprotected exposures to infected birds or other animals, or to environments contaminated by infected birds or other animals, are at greater risk of infection. CDC considers HPAI A(H5N1) viruses to have the potential to cause severe disease in infected humans and recommends the following:

Recommendations for the Public

Avoid exposure to sick or dead animals. If you are unable to avoid exposure, avoid unprotected (not using respiratory and eye protection) exposures to sick or dead animals including wild birds, poultry, other domesticated birds, and other wild or domesticated animals, as well as with animal feces, litter, or materials contaminated by birds or other animals with suspected or confirmed HPAI A(H5N1) virus infection.

Personal protective equipment (PPE) should be worn when in direct or close contact (within about six feet) with sick or dead animals including poultry, wild birds, backyard bird flocks, or other animals, animal feces, litter, or materials potentially contaminated with HPAI A(H5N1) viruses. PPE includes properly fitted unvented or indirectly vented safety goggles, disposable gloves, boots or boot covers, a NIOSH-Approved particulate respirator (e.g., N95^® filtering facepiece respirator, ideally fit-tested), disposable fluid-resistant coveralls, and disposable head cover or hair cover. Adding a face shield over the top of goggles and a fluid resistant apron can enhance protection. Additional information on PPE recommendations for workers can be found online.

Cook poultry, eggs, and beef to a safe internal temperature to kill bacteria and viruses. Refer to CDC's safer foods table for a complete list of safe internal temperatures. Choosing pasteurized milk and products made with pasteurized milk is the best way to keep you and your family safe. Unpasteurized (raw) milk and products made from raw milk, including soft cheese, ice cream, and yogurt, can be contaminated with germs that can cause serious illness, hospitalization, or death. Pasteurization kills bacteria and viruses, like avian influenza A viruses, in milk.

People exposed to HPAI A(H5N1)-virus infected birds or other animals (including people wearing recommended PPE) should monitor themselves for new respiratory illness symptoms, and/or conjunctivitis (eye redness), beginning after their first exposure and for 10 days after their last exposure. Influenza antiviral post-exposure prophylaxis can be considered to prevent infection, particularly in those who had unprotected exposure to HPAI A(H5N1)-virus infected birds or other animals (more information below). Persons who develop any illness symptoms after exposure to HPAI A(H5N1) virus infected birds or other animals should seek prompt medical evaluation for possible influenza testing and antiviral treatment by their clinician or public health department. Symptomatic persons should isolate away from others, including household members, except for seeking medical evaluation until it is determined that they do not have HPAI A(H5N1) virus infection.

Recommendations for Protecting Poultry and Livestock Owners and Workers

Employers should take steps to reduce workers' exposure to novel influenza A viruses such as HPAI A(H5N1) virus from sick animals or contaminated environments. Workers may be exposed when working with animals confirmed or potentially infected with novel influenza A viruses or working with materials, including raw milk, that are confirmed or potentially contaminated with novel influenza A viruses. Examples of potentially exposed workers include:

• Poultry and dairy and other livestock farmers and workers

• Veterinarians and veterinary staff

• Animal health responders

• Public health responders

• Dairy laboratory workers

• Food processing workers handling raw milk and other confirmed or potentially contaminated materials

• Slaughterhouse workers performing certain tasks on lactating dairy cattle including:

1. Unloading or handling live lactating dairy cattle for slaughter, including working in holding pens and tasks involved with ante-mortem inspection
2. Post-mortem processes including the post-mortem inspection, handling, and transporting of viscera
3. Removing and transporting udders from dairy cattle for further processing or rendering

To protect workers who might be exposed, employers should update or develop a workplace health and safety plan, conduct a site-specific hazard assessment to identify potential exposures based on work tasks and setting, and use the hierarchy of controls to identify controls to reduce or eliminate hazards including exposure to HPAI A(H5N1) viruses.

CDC has identified the types of controls that should be used to reduce exposures based on current understanding of the exposure level associated with different work tasks and settings.

For more information and full recommendations, visit:

• Interim Guidance for Employers to Reduce the Risk of Novel Influenza A for People Working with or Exposed to Animals

• Information for Workers Exposed to H5N1 Bird Flu

Recommendations for Clinicians

Clinicians should consider the possibility of HPAI A(H5N1) virus infection in persons showing signs or symptoms of acute respiratory illness or conjunctivitis who have relevant exposure history. More information is available at Brief summary for Clinicians. This includes persons who have had contact with potentially infected sick or dead birds, livestock, or other animals within 10 days before symptom onset (e.g., handling, slaughtering, defeathering, butchering, culling, preparing for consumption or consuming uncooked or undercooked food or related uncooked food products, including unpasteurized (raw) milk or other unpasteurized dairy products), direct contact with water or surfaces contaminated with feces, unpasteurized (raw) milk or unpasteurized dairy products, or parts (carcasses, internal organs, etc.) of potentially infected animals; and persons who have had prolonged exposure to potentially infected birds or other animals in a confined space. Clinicians should contact the state public health department to arrange testing for influenza A(H5N1) virus, collect recommended respiratory specimens (more information below) using PPE, consider starting empiric antiviral treatment (more information below), and encourage the patient to isolate at home away from their household members and not go to work or school until it is determined they do not have avian influenza A virus infection. Testing for other potential causes of acute respiratory illness should also be considered depending upon the local epidemiology of circulating respiratory pathogens, including SARS-CoV-2.

Recommendations for State Health Departments

State health department officials should investigate potential human cases of HPAI A(H5N1) virus infection as described below and should notify CDC within 24 hours of identifying a case under investigation. Rapid detection and characterization of novel influenza A viruses in humans remain critical components of national efforts to prevent further cases, to allow for evaluation of clinical illness associated with them, and to assess the ability of these viruses to spread from human to human. State Health Department officials, including the State Public Health Veterinarian, should collaborate with State Department of Agriculture and State Wildlife officials using a One Health approach when relevant to investigate suspected HPAI A(H5N1) infections in people linked with animals.

Recommendations for Monitoring and Testing

People exposed to HPAI A(H5N1)-infected birds or other animals (including people wearing recommended PPE) should be monitored for signs and symptoms of acute respiratory illness beginning after their first exposure and for 10 days after their last exposure. Patients who meet Epidemiologic criteria AND either Clinical OR Public Health Response criteria below should be tested for HPAI A(H5N1) virus infection by reverse-transcription polymerase chain reaction (RT-PCR) assay using H5-specific primers and probes at your state or local public health department.

Epidemiological Criteria

Persons with recent exposure (within 10 days) to HPAI A(H5N1) virus through one of the following:

• Exposure to HPAI A(H5N1) virus infected birds or other animals defined as follows:
  • Close exposure (within six feet) to birds or other animals, with confirmed avian influenza A(H5N1) virus infection. Bird or other animal exposures can include, but are not limited to handling, slaughtering, defeathering, butchering, culling, or preparing birds or other animals for consumption, or consuming uncooked or undercooked food or related uncooked food products, including unpasteurized (raw) milk, OR
  • Direct contact with surfaces contaminated with feces, unpasteurized (raw) milk or other unpasteurized dairy products, or bird or animal parts (e.g., carcasses, internal organs) from infected birds or other animals, OR
  • Visiting a live bird market with confirmed HPAI a(H5N1) virus infections in birds or associated with a case of human infection with HPAI A(H5N1) virus.
• Exposure to an infected person - Close (within six feet) unprotected (without use of respiratory and eye protection) exposure to a person who is a confirmed, probable, or symptomatic suspected case of human infection with HPAI A(H5N1) virus (e.g., in a household or healthcare facility).
• Laboratory exposure (unprotected exposure to HPAI A(H5N1) virus in a laboratory)

Clinical Criteria

Persons with signs and symptoms consistent with acute upper or lower respiratory tract infection, conjunctivitis or complications of acute respiratory illness without an identified cause. In addition, gastrointestinal symptoms such as diarrhea are often reported with HPAI A(H5N1) virus infection. Examples include but are not limited to:

• Mild illness (e.g., cough, sore throat, eye redness or eye discharge such as conjunctivitis, fever or feeling feverish, rhinorrhea, fatigue, myalgia, arthralgia, headache)
• Moderate to severe illness: (e.g., shortness of breath or difficulty breathing, altered mental status, seizures)
• Complications: pneumonia, respiratory failure, acute respiratory distress syndrome, multi-organ failure (respiratory and kidney failure), sepsis, meningoencephalitis

Public Health Response Criteria

Testing of asymptomatic persons for HPAI A(H5N1) virus infection is not routinely recommended. However, for the purpose of public health investigations as part of the response to the ongoing H5N1 situation, in consultation with state and local health departments, when feasible, offer a nasal/ oropharyngeal (OP) (+/- conjunctival) swab specimen test for influenza A(H5) virus using the CDC Influenza A/H5 subtyping kit to asymptomatic workers with high risk of exposure to HPAI A(H5N1) virus [e.g., exposed to animals infected with HPAI A(H5N1) virus who reported not wearing recommended PPE or who experienced a breach in recommended PPE], or asymptomatic close contacts of a confirmed case of HPAI A(H5N1) virus infection. Exposed persons should be actively monitored for signs and symptoms of acute respiratory illness or conjunctivitis for 10 days after the last known exposure to HPAI A(H5N1) virus. Any person who develops signs or symptoms of acute respiratory illness or conjunctivitis after high risk of exposure to HPAI A(H5N1) virus, including persons who previously tested negative for influenza A(H5) virus, persons who previously tested positive for influenza A(H5) virus while asymptomatic, and those receiving oseltamivir post-exposure prophylaxis, should be isolated, and tested for influenza A(H5) virus.

Preferred Clinical Specimens

For persons with suspected HPAI A(H5N1) virus infection, the following specimens should be collected as soon as possible after illness onset or when deemed necessary: a nasopharyngeal swab and a nasal swab combined with an oropharyngeal swab (e.g., two swabs combined into one viral transport media vial). The nasopharyngeal swab and the combined nasal-oropharyngeal swabs should be tested separately. If these specimens cannot be collected, a single nasal or oropharyngeal swab is acceptable. If the person has conjunctivitis (with or without respiratory symptoms), both a conjunctival swab and nasopharyngeal swab and/or nasal swab combined with an oropharyngeal swab should be collected. Patients with severe respiratory disease also should have lower respiratory tract specimens (e.g., an endotracheal aspirate or bronchoalveolar lavage fluid) collected, if possible. For severely ill persons, multiple respiratory tract specimens from different sites should be obtained to increase the potential for HPAI A(H5N1) virus detection.

Recommendations for Infection Prevention and Control

Standard, contact, and airborne precautions are recommended for patients presenting for medical care or evaluation who have illness consistent with influenza and recent exposure to birds or other animals potentially infected with HPAI A(H5N1) virus. For additional guidance on infection prevention and control precautions for patients who might be infected with HPAI A(H5N1) virus, please refer to guidance for infections with novel influenza A viruses associated with severe disease.

Recommendations for Influenza Antiviral Treatment and Chemoprophylaxis

Treating Symptomatic Persons with Dairy Cattle or Other Animal Exposures

Outpatients meeting epidemiologic exposure criteria who develop signs and symptoms compatible with influenza should be referred for prompt medical evaluation, testing, and empiric initiation of antiviral treatment with oseltamivir (twice daily x 5 days) as soon as possible. Clinical benefit is greatest when antiviral treatment is administered early, especially within 48 hours of illness onset.

Hospitalized patients who are confirmed, probable, or suspected cases of human infection with HPAI A(H5N1) virus, regardless of time since illness onset are recommended to initiate antiviral treatment with oral or enterically administered oseltamivir as soon as possible. Antiviral treatment should not be delayed while waiting for laboratory testing results.

Detailed guidance on dosing and treatment duration is available at Interim Guidance of the Use of Antiviral Medications for the Treatment of Human Infection with Novel Influenza A Viruses Associated with Severe Human Disease.

Treating Asymptomatic Persons with Bird or Other Animal Exposures Who Test Positive for Influenza A(H5) Virus

Asymptomatic persons exposed to animals infected with HPAI A(H5N1) virus who reported not wearing recommended PPE or who experienced a PPE breach in recommended PPE and who tested positive for influenza A(H5) virus should be offered oseltamivir treatment (unless already receiving oseltamivir post-exposure prophylaxis). Exposed asymptomatic persons who test positive for influenza A(H5) virus should wear a facemask when in close contact with others and should continue to be actively monitored for signs and symptoms of acute respiratory illness or conjunctivitis for 10 days after testing A(H5) positive. Any exposed person who tested positive for A(H5) virus while asymptomatic and who develops signs or symptoms of acute respiratory illness or conjunctivitis while receiving oseltamivir for treatment or post-exposure prophylaxis, should be isolated, and tested again for influenza A(H5) virus. Repeat testing is recommended to rule out initial A(H5) test positivity as a result of viral contamination, such as from an environmental exposure, that did not progress to infection (i.e., repeat testing yields a negative A(H5) result) and to allow for evaluation of development of antiviral resistance during treatment/prophylaxis if repeat testing is still positive for A(H5).

Chemoprophylaxis of Persons with Exposure to HPAI A(H5N1) Virus:

Antiviral chemoprophylaxis is not routinely recommended for persons who properly used (including when taking off) recommended PPE and experienced no breaches while handling sick or potentially infected birds or other sick or dead animals or decontaminating infected environments (including animal disposal).

Chemoprophylaxis with influenza antiviral medications can be considered for any person meeting epidemiologic exposure criteria. Decisions to initiate post-exposure antiviral chemoprophylaxis should be based on clinical judgment, with consideration given to the type of exposure, duration of exposure, time since exposure, and known infection status of the birds or animals the person was exposed to. Antiviral chemoprophylaxis is not an alternative for use of appropriate PPE and engineering and administrative controls, and receipt of PEP should not be contingent upon acceptance of and participation in influenza testing. When feasible, offer oral oseltamivir for post-exposure prophylaxis (PEP) and influenza A(H5) testing to asymptomatic individuals who experienced high risk of exposure to HPAI A(H5N1) virus:

*Oseltamivir PEP [twice daily x 5 days (treatment dosing)] can be given to persons who experienced high risk of exposure (without using recommend PPE) to animals confirmed to be infected or highly suspected to be infected with HPAI A(H5N1) virus. An unprotected exposure could also include breaches in or failures of recommended PPE. Examples of persons with high risk of exposure to sick/dead animals with confirmed or highly suspected with HPAI A(H5N1) can include:

• Members of poultry culling teams responding to poultry outbreaks not using recommended PPE who had direct or close contact with sick/dead poultry;
• Persons working at small or large farms not using recommended PPE who had direct or close contact with sick/dead poultry;
• Dairy farm workers not using recommend PPE who were splashed in the face with raw cow milk by dairy cows;
• Persons not using recommended PPE who handled or cared for sick or dead birds;
• Zoo personnel or workers at animal sanctuaries or animal rehabilitation centers not using recommended PPE who had direct or close unprotected exposure to sick/dead birds or other sick/dead animals;
• Veterinary personnel and owners of domestic pets not using recommended respiratory and eye protection who handled, cared for, or performed necropsies on sick wild or domesticated animals that died.

*Longer duration of oseltamivir PEP (e.g., twice daily for 10 days) can be given for ongoing high risk of exposure (e.g., inadequate PPE) to infected animals.

Antiviral chemoprophylaxis is not routinely recommended for personnel who used proper PPE and experienced no breaches while handling sick or potentially infected birds or other infected animals or decontaminating infected environments (including animal disposal).

If antiviral chemoprophylaxis is initiated, oseltamivir treatment dosing (one dose twice daily) is recommended instead of the antiviral chemoprophylaxis regimen for seasonal influenza. Specific dosage recommendations for treatment by age group is available at Influenza Antiviral Medications: Summary for Clinicians. Physicians should consult the manufacturer's package insert for dosing, limitations of populations studied, contraindications, and adverse effects. If exposure was time-limited and not ongoing, five days of medication (one dose twice daily) from the last known exposure is recommended.

Monitoring and Antiviral Chemoprophylaxis of Close Contacts of Persons with HPAI A(H5N1) virus infection: Recommendations for monitoring and chemoprophylaxis of close contacts of infected persons are different than those that apply to persons who meet bird or other animal exposure criteria. Post-exposure prophylaxis of close contacts of a person with HPAI A(H5N1) virus infection is recommended with oseltamivir twice daily (treatment dosing) instead of the once daily pre-exposure prophylaxis dosing. Detailed guidance is available at Interim Guidance on Follow-up of Close Contacts of Persons Infected with Novel Influenza A Viruses and Use of Antiviral Medications for Chemoprophylaxis.

Vaccination

No human vaccines for prevention of HPAI A(H5N1) virus infection are currently available in the United States. Seasonal influenza vaccines do not provide protection against human infection with HPAI A(H5N1) viruses.

Attribution Statement

N95 and NIOSH Approved are certification marks of the U.S. Department of Health and Human Services (HHS) registered in the United States and several international jurisdictions.

Appendix: Interim Risk Categories by Exposure Table

Categories of individual risk for influenza A(H5N1) virus infection by setting and exposure, including exposure to infected poultry or dairy cows, contaminated animal products, and other suspected infected peri-domestic animals.

Last updated: November 7, 2024

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