H5N1 Influenza Information and Resources

Highly pathogenic avian influenza (HPAI) can be caused by several different strain types. H5N1 was initially detected in 1996 and has primarily been found in wild birds. Although transmission directly from birds to humans is unusual, transmission from birds to other mammals occurs more frequently. Sporadic outbreaks in several species of mammals (both terrestrial, including commercial poultry, and marine species) have occurred and are increasing in frequency.

In the spring of 2024, an outbreak of HPAI A(H5N1) 2.3.4.4b clade was reported in cows across multiple states. As of March 2025, H5N1 has been detected in nearly 1000 cattle herds among 17 states, but this number is likely an underestimate. The most recent H5N1 dairy cattle data are reported by the U.S. Department of Agriculture (USDA). It is known that milk from infected cows contains H5N1. Although no human H5N1 cases have occurred, animals that have consumed raw milk (mice and cats) have become infected with H5N1. The FDA has confirmed that pasteurization inactivates H5N1 in milk. These findings highlight the safety of the commercial milk supply in the US and give warning of the dangers of raw milk consumption.

While cows are known to occasionally contract influenza viruses, this marks the first documented outbreak involving highly pathogenic strains in cattle. Furthermore, surveillance through the National Milk Testing Strategy have now spillover events from wild birds into cattle (separate from the B3.13 genotype that has thus far been circulating in the US). Notably, this is the genotype that was previously identified in two severe human cases in North America (teenager in British Columbia, and the fatal case in Louisiana).

Poultry has similarly been severely affected in every US state. The impact on poultry and layer farms across the country is already showing a significant economic impact, with the prices of eggs projected to continue to rise. The most recent H5N1 poultry data are reported by the CDC.

There continues to be even more mammalian spread over the last few months. The most noteworthy is the reports of illness in domestic cats. To date, these cases have typically been from exposure to contaminated raw cat food or to other ill animals. However, there was a recent report published by the CDC of H5N1 detection in indoor domestic cats that resided in households of symptomatic dairy workers and without other known direct exposure. There has not been any more evidence of sustained transmission in pigs.

While the likelihood of getting H5N1 in the US is currently very low, the findings in the section above highlight the growing risk of potential exposure to H5N1 from infected animals in the US. The CDC provides a risk assessment of H5N1 in the US. The majority of US cases have been related to occupational exposures to infected animals. There have not yet been any cases of human-to-human transmission. The CDC provides measures that can be taken to reduce risk of exposure. Those most relevant to children include avoiding avoid direct contact with sick or dead wild birds, poultry, and other animals and to never consume raw milk.

As of March 10, 2025, 70 confirmed human cases of H5N1 have been reported across 14 states. The most recent data for H5N1 disease in humans, and the states impacted, are reported by the CDC. The clinical characteristics of H5N1 were summarized in December 2024 in the New England Journal of Medicine. In that report, the majority of cases were mild, predominantly conjunctivitis, and of short duration. However, the potential to cause severe respiratory disease has been observed. To date, there has been one human death, an adult in Louisiana with exposure to backyard flocks of H5N1-infected birds.

H5N1 cases in children have been infrequent. Although ages of patients not formally reported by the CDC, it is thought that two of the 70 cases of H5N1 in the US were in children, and both were very mild illnesses. However, a severe case of H5N1 was reported in adolescent in British Columbia, Canada, highlighting the potential for H5N1 to cause severe disease in children.

A recent CDC seroprevalence study dairy workers exposed to H5N1-infected cows revealed that 7% had detectable antibodies, with 50% of seropositive individuals being asymptomatic, underscoring the potential for subclinical infections among those with occupational exposure. To add to this, another recent seroprevalence study, this time in 150 bovine veterinary workers, revealed evidence of recent infection in three individuals – two without exposures to animals with known or suspected HPAI (with one practicing in a state where H5N1 infected cattle has not been reported), while one also worked with known HPAI-positive poultry.

All children with conjunctivitis and/or a respiratory illness, particularly a severe respiratory illness, should be screened for the following exposures:

• Close contact with an animal and/or human with known/suspected H5N1
• Consumption of raw milk
• Close contact with dairy cows or poultry
• Close contact with wild birds

Some laboratory tests for seasonal influenza may provide clues that a child may be infected with H5N1. For example, the Biofire Respiratory Pathogen Panel, a multiplex PCR panel commonly used at children’s hospitals to detect multiple respiratory viruses and bacteria, is able to identify influenza A and the common seasonal subtypes (H1 and H3). If that panel identifies non-subtyped influenza A, it is possible that the patient is infected with H5N1 and requires further testing. In the diagnostics section below, additional guidance for who should undergo testing is provided based on CDC recommendations.

If any the above Identify concern for H5N1, the following measures should be taken (additional details in the following section):

• Isolate: Take appropriate infection control precautions
• Inform: Notify your local infection control team and the local health department
• Coordinate influenza A testing (if not yet performed) and, if positive, H5N1 subtyping

When H5N1 is suspected, the child and their family should be promptly Isolated and personal protective equipment (PPE) should be used. Specifically, the following steps should be taken:

• Place the patient in an airborne infection isolation room (AIIR).
• If an AIIR is not available, place the patient in a negative airflow room until an AIIR is available. If neither are available, place the patient in a private room with the door closed until the patient can be safely transferred to a center with an AIIR. If the room being utilized recirculates air without external exhaust and/or HEPA-filtration, use of a portable HEPA-filtered air purifier, if available, may be prudent in this situation but is not formally recommended by the CDC.
• Provide care to the patient using contact and airborne precautions. PPE in this situation includes gown, gloves, N95 respirator, and eye protection.

The CDC provides detailed infection prevention and control recommendations for healthcare facilities.

After a history and examination is completed with the above precautions, if H5N1 is still being considered, clinicians should Inform their local infection prevention and control team and/or the local health department. They will advise on additional prevention measures and testing procedures.

H5N1 subtyping is not routinely available at children’s hospitals. Some commercial reference laboratories offer H5N1 testing, but the preferred route in many jurisdictions may be for subtyping through the local public health laboratory. Clinicians should familiarize themselves with the H5N1 testing options and procedures at their children’s hospital and/or their local department of public health. The CDC offers H5N1 testing guidance to clinicians and is summarized below.

1. Perform testing for influenza A in the following situations, preferably with an assay that is able to provide seasonal influenza A subtyping data*.
   • Children with conjunctivitis and/or a respiratory illness with a history of possible exposure to H5N1
   • All hospitalized children^ with influenza A, particularly those who are critically ill.
     * Clinicians should familiarize themselves with the influenza testing options available to them and their ability to provide seasonal influenza subtyping data.
     ^ See additional information below regarding H5N1 typing strategies based on jurisdiction.
2. If the test is positive for influenza A, assess if the test can reliably rule out H5N1.
   • If the assay does not provide subtyping data, additional H5N1 testing is required.
   • If the assay provides subtyping data, H5N1 can be ruled out if the test identifies a seasonal influenza A virus subtype (i.e., H1 or H3). If a seasonal subtype is not identified, additional H5N1 testing is required.
   • Clinicians should work with their laboratory to ensure prompt notifications to front-line staff is provided if a non-subtyped influenza A virus is identified to ensure there is awareness of the possibility of H5N1.
3. After discussion with the local infection prevention and control team and/or the local health department, the previously collected sample should be sent for H5N1 subtyping to appropriate public health or reference laboratory.

^ While the CDC recommends H5N1 subtyping of influenza A-positive samples from all hospitalized patients, some jurisdictions may have additional guidance for hospitals to manage the volume of testing, especially during seasonal influenza season. Clinicians should familiarize themselves with the recommendations within their jurisdiction from their local health department. At the discretion of the jurisdiction, some strategies to manage H5N1 testing volumes may include one or more of the following:

• Utilizing assays that provide seasonal influenza A subtyping data for all children admitted with a respiratory illness or reflexively performing those assays in hospitalized children from a sample that initially tests positive for influenza A with an assay without subtyping data.
  • H5N1 typing would only be required on those samples that do not identify a seasonal influenza A virus subtype (i.e., H1 or H3).
• If a seasonal influenza A subtyping assay is not available, sending H5N1 typing from all critically ill patients testing positive for influenza A.
• If a seasonal influenza A subtyping assay is not available, and if H5N1 typing is only requested for critically ill patients, additional H5N1 typing may be based on presence of risk factors through routine screening or sending H5N1 typing from a convenience sample of non-critically ill hospitalized patients testing positive for influenza A.
• Some children’s hospitals may have a laboratory-developed H5N1 assay that can be performed with the guidance and oversight from the local health department.

The CDC recommends prompt initiation of antiviral treatment in children with suspected or confirmed H5N1. Pediatric infectious diseases consultation can guide the appropriate antiviral and dosing. If pediatric infectious diseases is unavailable, the local health department and/or adult infectious diseases may assist in treatment decision making.

H5N1 is susceptible to currently available influenza antivirals. Most frequently, oseltamivir will be used. Combination therapy can be considered for hospitalized patients, especially for those who are critically ill.  Pediatric dosing is available from the American Academy of Pediatrics.

H5N1 Epidemiology and Risk

CDC | Risk to People in the United States from Highly Pathogenic Avian Influenza A(H5N1) Viruses

CDC | H5 Bird Flu: Current Situation

H5N1 Clinical Guidance

CDC | Prevention and Antiviral Treatment of Avian Influenza A Viruses in People

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

CDC | Clinician Brief: Evaluating and Managing Patients Exposed to Animals or Persons Infected with Novel Influenza A Viruses of Public Health Concern

CDC | Interim Guidance on the Use of Antiviral Medications for Treatment of Human Infections with Novel Influenza A Viruses Associated with Severe Human Disease

CDC | Accelerated Subtyping of Influenza A in Hospitalized Patients

AAP | Recommendations for Prevention and Control of Influenza in Children, 2023–2024

Key H5N1 publications in children

New England Journal of Medicine | Critical Illness in an Adolescent with Influenza A(H5N1) Virus Infection