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H5 Viral Particle

Avian Influenza A(H5) Outbreak

Current US Outbreak

As of December 5, 2024: 

Critical Epidemiological Updates

  • California state agriculture officials have identified a second sample of milk infected with H5N1 from Raw Farm, LLC and temporarily banned distribution of milk from the farm while the infected herd recovers.  The prevalence of H5N1 in the US raw milk supply is currently unknown. Pasteurizing milk is the only known safe way to eliminate the risk of H5N1 in dairy products. Therefore, we strongly recommend that individuals only consume pasteurized milk and other dairy products.
  •  A recent publication in Nature highlights how the H5N1 virus has changed over time, with the 2024 strain from Texas showing more viral shedding in the air than previous H5N1 strains. This study adds to the growing evidence that the H5N1 2.3.4.4b clade has become better adapted for mammals in recent years. However, the circulating strains in the US do not show mutations at this time that are necessary for efficient airborne or human-to-human transmission.

Routine Surveillance Updates

  • The Centers for Disease Control and Prevention (CDC) is reporting 58 confirmed human cases of H5 in the United States Outbreak as of December 5, 2024. Two of these cases have not had a known source of infection and reported no contact with animals or raw milk. No new cases have been reported since the last risk assessment on November 26, 2024.
  • The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) has reported 273 new infected cattle herds across two states (UT, CA) in the last 30 days, bringing the total for the outbreak to 718 cattle herds in 15 states. This represents a slight increase compared to the previous 30 days.
  • CDC reports that for the duration of the outbreak, 260 tests for poultry workers and 146 tests for dairy workers have been sent to CDC for H5N1 testing, resulting in a positivity rate since March 2024 of 8.07% (21/260) and 23.97% (35/146), respectively.