The physical space of the MSK Library is permanently closed to visitors as of Friday, May 17, 2024. Please visit this guide for more information.
The physical space of the MSK Library is permanently closed to visitors as of Friday, May 17, 2024. Please visit this guide for more information.
Confirmed and probable cases are typically updated by 5 PM EST on Mondays (for cases confirmed by CDC on Friday, Saturday, or Sunday), Wednesdays (for cases confirmed by CDC on Monday or Tuesday), and Fridays (for cases confirmed by CDC on Wednesday and Thursday). Affected states may report cases more frequently.
| Exposure Associated with Commercial Agriculture & Related Operations | |||||
| State | Dairy Herds (Cattle) | Poultry Farms & Culling Operations | Other Animal Exposure | Exposure Source Unknown | State Total |
| California | 36 | 0 | 0 | 2 | 38 |
| Colorado | 1 | 9 | 0 | 0 | 10 |
| Iowa | 0 | 1 | 0 | 0 | 1 |
| Louisiana | 0 | 0 | 1 | 0 | 1 |
| Michigan | 2 | 0 | 0 | 0 | 2 |
| Missouri | 0 | 0 | 0 | 1 | 1 |
| Nevada | 1 | 0 | 0 | 0 | 1 |
| Ohio | 0 | 1 | 0 | 0 | 1 |
| Oregon | 0 | 1 | 0 | 0 | 1 |
| Texas | 1 | 0 | 0 | 0 | 1 |
| Washington | 0 | 11 | 0 | 0 | 11 |
| Wisconsin | 0 | 1 | 0 | 0 | 1 |
| Wyoming | 0 | 0 | 1 | 0 | 1 |
| Source Total | 41 | 24 | 2 | 3 | 70 |
NOTE: One additional case was previously detected in a poultry worker in Colorado in 2022. Louisiana reported the first H5 bird flu death in the U.S.
When a case tests positive for H5 at a public health laboratory but testing at CDC is not able to confirm H5 infection, per Council of State and Territorial Epidemiologists (CSTE) guidance, a case is reported as probable.
Confirmed and probable cases are typically updated by 5 PM EST on Mondays (for cases confirmed by CDC on Friday, Saturday, or Sunday), Wednesdays (for cases confirmed by CDC on Monday or Tuesday), and Fridays (for cases confirmed by CDC on Wednesday and Thursday). Affected states may report cases more frequently.
This is a technical summary of an analysis of the genomic sequences of the viruses identified in two upper respiratory tract specimens from the patient who was severely ill from an infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus in Louisiana. CDC has sequenced the influenza viruses in specimens collected from the patient in Louisiana who was infected with, and became severely ill from HPAI A(H5N1) virus. The genomic sequences were compared to other HPAI A(H5N1) sequences from dairy cows, wild birds and poultry, as well as previous human cases and were identified as the D1.1 genotype. The analysis identified low frequency mutations in the hemagglutinin gene of a sample sequenced from the patient, which were not found in virus sequences from poultry samples collected on the patient’s property, suggesting the changes emerged in the patient after infection.
The genomes of the virus (A/Louisiana/12/2024) from each clinical specimen are publicly posted in GISAID (EPI_ISL_19634827 and EPI_ISL_19634828) and GenBank (PQ809549-PQ809564).
This is a technical summary of an analysis of the genomic sequence data for an influenza A(H5N1) virus from a pediatric case in California that was confirmed by CDC on November 22. Although the genetic data generated were insufficient to classify the virus as a specific genotype, the virus gene segments sequenced most closely resemble those segments from recent B3.13 viruses detected in California in humans, dairy cattle and poultry.
CDC and Stanford Medicine have submitted these data for A/California/192/2024 to both the GISAID and GenBank databases with accession numbers EPI_ISL_19597300 and PQ724471-PQ724473, respectively.
CDC has sequenced the influenza virus genome identified in a conjunctival specimen collected from the person in Michigan who was identified to be infected with HPAI A(H5N1) virus and compared each gene segment with HPAI A(H5N1) sequences from cows, wild birds and poultry and the first human case in Texas. The virus HA was identified as clade 2.3.4.4b with each individual gene segment closely related to genotype B3.13 viruses detected in dairy cows available from USDA testing. No amino acid changes were identified in the HA gene sequence from the Michigan patient specimen compared to the HA sequence from the case in Texas and only minor changes were identified when compared to sequences from cows. These data indicate viruses detected in both cows and the two human cases maintain primarily avian genetic characteristics and lack changes that would make them better adapted to infect or transmit between humans. The genome of the human virus from Michigan did not have the PB2 E627K change detected in the virus from the Texas case but had one notable change (PB2 M631L) compared to the Texas case that is known to be associated with viral adaptation to mammalian hosts, and which has been detected in 99% of dairy cow sequences but only sporadically in birdsA. This change has been identified as resulting in enhancement of virus replication and disease severity in mice during studies with avian influenza A(H10N7) virusesB. The remainder of the genome of A/Michigan/90/2024 was closely related to sequences detected in infected dairy cows and strongly suggests direct cow-to-human transmission.
The genome of the virus identified from the patient in Michigan (A/Michigan/90/2024) is publicly posted in GISAID (EPI_ISL_19162802) and has been submitted to GenBank (PP839258-PP839265).
CDC has sequenced the influenza virus genome identified in a specimen collected from the patient in Texas who was confirmed to be infected with highly pathogenic avian influenza A(H5N1) ["HPAI A(H5N1)"] virus and compared these with HPAI A(H5N1) sequences from cattle, wild birds and poultry. The virus sequences are HA clade 2.3.4.4b HPAI A(H5N1) with each individual gene segment closely related to viruses detected in dairy cattle available from USDA testing in Texas. While minor changes were identified in the virus sequence from the patient specimen compared to the viral sequences from cattle, both cattle and human sequences maintain primarily avian genetic characteristics and for the most part lack changes that would make them better adapted to infect mammals. The genome for the human isolate had one change (PB2 E627K) that is known to be associated with viral adaptation to mammalian hosts, and which has been detected before in people and other mammals infected with HPAI A(H5N1) virus and other avian influenza subtypes (e.g., H7N9), but with no evidence of onward spread among people.
The genome of the virus identified from the patient in Texas is publicly posted in GISAID and has been submitted to GenBank.
As of February 24, CDC has confirmed three human cases of H5 bird flu in people who became ill in 2025: a dairy worker with exposure to infected dairy cows (Nevada), a poultry worker with exposure to infected commercial poultry (Ohio), and the owner of an infected backyard poultry flock (Wyoming). These are all considered higher-risk exposures. While the dairy worker was not hospitalized, both people with poultry exposures experienced severe illness and were hospitalized. Both hospitalized cases were confirmed positive from lower respiratory specimens, including a bronchoalveolar lavage and sputum. To date, there has been no evidence of onward spread from any of these people to anyone else.
Nevada Dairy Worker
The dairy worker in Nevada had conjunctivitis (eye redness and irritation) and has recovered. Most infections associated with U.S. dairy cows to date have involved mild respiratory symptoms or conjunctivitis. This person was exposed to infected dairy cows and tested positive for avian influenza A(H5N1) virus.
CDC's analysis of the genetic sequence of the virus isolated from the patient in Nevada identified the virus as an avian influenza A(H5N1) virus from clade 2.3.4.4.b (genotype D1.1). The nucleotide sequence was nearly identical to that of the viruses that USDA reported from dairy cows in Nevada that the person worked with. The virus had a genetic mutation in its polymerase basic 2 (PB2) protein that has previously been associated with more efficient virus replication in mammalian cells (i.e., change of PB2 D701N). This change was previously identified in a human case in Chile in 2023.
The poultry worker in Ohio had respiratory symptoms and is home and recovering. This person participated in culling activities on a farm with infected poultry. The initial upper respiratory specimens could not be confirmed as positive for avian influenza A(H5) virus at CDC, so CDC initially reported this as a probable case; a subsequent specimen from the person was confirmed positive for avian influenza A(H5) virus at CDC.
Sequencing data are not yet available for the Ohio case.
The backyard flock owner in Wyoming had respiratory symptoms and is reported to have underlying health conditions that can make people more vulnerable to severe influenza illness. This person has been discharged from the hospital and is recovering. This person had direct contact with poultry infected with avian influenza A(H5) virus that died on their property. Initial upper respiratory specimens were negative for influenza viruses; a lower respiratory specimen collected several days later in the hospital was positive for avian influenza A(H5N1) virus.
CDC's analysis of the genetic sequence of the virus from the patient in Wyoming identified an avian influenza A(H5N1) virus from clade 2.3.4.4.b (genotype D1.1). The virus had a genetic mutation in its PB2 protein that has previously been associated with more efficient virus replication in people and other mammals (i.e., change of PB2 E627K). This change was previously identified in a human case in Texas during 2024.
The CDC has multiple surveillance systems that monitor national, state, and local level influenza data, including:
Influenza virus and illness activity are monitored year-round through a collaborative effort between CDC and many partners, including state, local, and territorial health departments; public health and clinical laboratories; clinics; and emergency departments.
This data is used year-round to monitor key flu indicators. These data are reviewed comprehensively each week.
Weekly Snapshot for the Week Ending: February 21, 2025
| Case Reporting |
5 cases detected through national flu surveillance |
|---|---|
| Public Health Laboratory Monitoring | Since February 25, 2024, 136,134+ specimens tested using a protocol that would have detected influenza A(H5) or other novel influenza viruses |
| Clinical Laboratory Trends |
CDC has not identified any unusual trends in reported clinical laboratory data at the national, state, or local levels. |
| Emergency Departments |
CDC has not identified any unusual trends in emergency department visits associated with influenza or potentially related symptoms at the national, state, or local levels. |
| Wastewater Surveillance | For the week ending February 15, 2025, 360 sites reported results for avian influenza A(H5) in wastewater, and 12 (3.3%) sites from 3 states (California, Connecticut, New Jersey) reported H5 detections. |
CDC numbers are based on weekly state aggregate reports since 2022. CDC defers to states for updated information on people being monitored and tested. March 24, 2024, was the date of the first reported dairy cow infections in the United States.
| February 2022 - Present |
CDC and state and local health departments monitor people exposed to infected birds, poultry, dairy cows or other animals for 10 days after exposure. Between February 2022 and now, there have been:
|
|---|---|
| Current HPAI Outbreak (2024) | CDC and state and local health departments monitor people exposed to infected birds, poultry, dairy cows and other animals for 10 days after exposure. Between March 24, 2024, and now, there have been:
66 human cases detected through targeted H5 surveillance |
Please see the below Health Advisory from the Centers for Disease Control and Prevention (CDC) regarding accelerated subtyping for influenza A specimens among hospitalized individuals testing positive for influenza.
Although the ongoing global outbreak of highly pathogenic avian influenza A(H5N1) virus has primarily affected dairy cows, poultry, and other animals, 66 human cases (including one death) have been identified in the United States in 2024. CDC is now recommending ordering subtyping for all influenza A-positive specimens collected from hospitalized individuals within 24 hours of hospital admission to help rapidly detect any human cases of avian influenza A(H5N1).