Bird Flu Risk Remains Low, Despite First Reported Death

A total of 954 cases of avian influenza—also known as H5N1 and the bird flu—have been reported globally since the World Health Organization (WHO) began tracking the infectious disease in 2003, and of that total, close to half (48.6%, or 464) of the cases have resulted in death. For the years 2003 to 2009 and 2010 to 2014 alone, there were 468 and 233 cases, and 282 and 125 deaths, respectively.¹

In stark contrast, the first US death was reported by the Louisiana Department of Health on January 6; there was just 1 case reported in the US overall in 2022 and 66 reported in the following years.² As of December 6, 2024, only 58 cases had been confirmed in the US.³

Not all states have seen cases, however. At present, besides Louisiana—where the patient death remains the only human case of H5N1 in the state⁴—cases have been confirmed in California (n = 37), Colorado (n = 10), Iowa (n = 1), Michigan (n = 2), Oregon (n = 1), Texas (n = 1), Washington (n = 11), and Wisconsin (n = 1).⁵ No person-to-person transmission has yet been identified overall.⁶

The individual who died had a severe case of the illness, was older than 65 years, and had underlying medical conditions. They were hospitalized in December following exposure to noncommercial backyard flock and wild birds,⁷ and their illness confirmed to be H5N1 by the CDC on December 18.⁸

Globally, close to half of confirmed bird flue cases have resulted in death compared with 1 linked death so far in the US. California has the most current confirmed cases. | Image Credit: © RafMaster-stock.adobe.com

The particular virus strains seen in 2 upper respiratory tract (nasopharyngeal and nasopharyngeal/oropharyngeal) samples taken from the now-deceased patient and sequenced by the CDC in December differed slightly in their genomic sequencing from the virus sequences seen in the samples taken from the birds from which the patient contracted avian influenza.⁹ These strains also differed from those seen in samples taken from wild birds and poultry and from previous human cases from British Columbia in Canada and Washington state in the US.

The genotype was the same, D1.1, however, leading the CDC to note the low frequency mutations likely occurred within the patient after infection. The data the CDC saw also were determined to be closely related to HPAI A(H5N1) candidate vaccine viruses currently available to manufacturers, indicating their potential to be used to develop vaccines if needed, the CDC explained.

At present in the US, no cases of human-to-human transmission of the bird flu have been reported, although a multistate outbreak was reported among dairy cattle,¹⁰ a widespread outbreak among wild birds,¹¹ and sporadic outbreaks among poultry and other mammals, as well as workers in those industries.^12,13 There are also, however, reports of widespread outbreaks in wild birds worldwide.⁹

Meanwhile, additional probable cases—probable because CDC testing was unavailable—have been reported in Washington, Arizona, California, and Delaware.⁵ California has the largest amount of human exposure incidents by far, at 34, which have all been linked to commercial agriculture and related operations.⁴

The overall health risk for the general public remains low, despite the potential for mutations in the bird flu protein making it easier for human infection to occur, with the CDC noting the lack of active spread of concerning virologic changes.² Very rarely does bird-to-human transmission overall occur, with the most likely method of infection being close contact with infected birds, in particular their feces or feathers. The risk is greatest in people who work with birds/poultry or cows or are recreationally exposed to them.⁷

References

1. Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003-2024. World Health Organization. Accessed January 9, 2025. https://cdn.who.int/media/docs/default-source/2021-dha-docs/cumulative-number-of-confirmed-human-cases-for-avian-influenza-a(h5n1)-reported-to-who--2003-2024.pdf?sfvrsn=6be054e0_1&download=true

2. First H5 bird flu death reported in United States. News release. CDC. January 6, 2025. Accessed January 9, 2025. https://www.cdc.gov/media/releases/2025/m0106-h5-birdflu-death.html

3. How CDC is monitoring influenza data among people to better understand the current avian influenza A (H5N1) situation. CDC. December 6, 2024. Accessed January 9, 2024. https://www.cdc.gov/bird-flu/h5-monitoring/index.html

4. Parkinson J, Abene S. The first patient in US with severe case of avian influenza dies. ContagionLive®. January 7, 2025. Accessed January 9, 2025. https://www.contagionlive.com/view/the-first-severe-case-of-avian-influenza-confirmed-in-the-united-states

5. H5 bird flu: current situation. CDC. Updated January 8, 2025. Accessed January 9, 2025. https://www.cdc.gov/bird-flu/situation-summary/index.html

6. Louisiana reports first H5N1 bird flu death in U.S. American Hospital Association. January 7, 2025. Accessed January 9, 2025. https://www.aha.org/news/headline/2025-01-07-louisiana-reports-first-h5n1-bird-flu-death-us#:~:text=The%20Louisiana%20Department%20of%20Health,backyard%20flock%20and%20wild%20birds

7. LDH reports first U.S. H5N1-related human death. News release. Louisiana Department of Health. January 6, 2025. Accessed January 9, 2025. https://ldh.la.gov/news/H5N1-death

8. CDC confirms first severe case of H5N1 bird flu in the United States. CDC. December 18, 2024. Accessed January 9, 2025. https://www.cdc.gov/media/releases/2024/m1218-h5n1-flu.html

9. Genetic sequences of highly pathogenic avian influenza A(H5N1) viruses identified in a person in Louisiana. CDC. December 26, 2024. Accessed January 9, 2025. https://www.cdc.gov/bird-flu/spotlights/h5n1-response-12232024.html

10. HPAI confirmed cases in livestock. US Department of Agriculture. Updated December 20, 2024. Accessed January 9, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/hpai-confirmed-cases-livestock

11. Detections of highly pathogenic avian influenza in wild birds. USDA. January 03, 2025. Accessed January 9, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/wild-birds

12. Confirmations of highly pathogenic avian influenza in commercial and backyard flocks. USDA. Updated June 20, 2024. Accessed January 9, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/commercial-backyard-flocks

13. Detections of highly pathogenic avian influenza in mammals. USDA. Updated January 6, 2025. Accessed January 9, 2025. https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/mammals