Avian influenza A (H5N1) virus infection

Further h​uman cases of bird flu associated with outbreak in poultry and dairy cattle in the US

Avian influenza A(H5N1) virus is currently causing a multistate outbreak in poultry and dairy cows in the US. While outbreaks have previously been reported in poultry, this is the first time the virus has been detected in cows. Cases of human infection linked to the outbreak in dairy cows have been reported, and these cases represent the first instances of likely mammal-to-human transmission globally.

As of 16 October 2024, 25 cases of human infection associated with exposure to infected poultry or dairy cows have been reported in 2024 across five states - Texas, Michigan, Colorado, Missouri, and California. Of the 25 cases, 15 occurred following exposure to infected dairy cows, 9 occurred following exposure to infected poultry, and 1 case had no known animal exposure. No deaths have been reported. Prior to this outbreak, the first and only human case of infection ever reported in the US was in 2022 in Colorado, and was associated with direct exposure to infected poultry during a culling process.[22]Centers for Disease Control and Prevention. H5 bird flu: current situation. Oct 2024 [internet publication]. https://www.cdc.gov/bird-flu/situation-summary/index.html

Updated situation summaries are available from the Centers for Disease Control and Prevention (CDC), and are being updated regularly:

• CDC: H5 bird flu - current situation Opens in new window

As part of the current outbreak, people with exposure to infected (or potentially infected) birds, cows, or other domestic or wild animals are being monitored and tested if they develop influenza-like symptoms. At least 5000 people with potential exposure have been monitored in the US since March 2024.​ The CDC currently considers the public health risk to be low.[22]Centers for Disease Control and Prevention. H5 bird flu: current situation. Oct 2024 [internet publication]. https://www.cdc.gov/bird-flu/situation-summary/index.html In the UK, the UK Health Security Agency (UKHSA) considers the risk to the public to be very low.[36]UK Health Security Agency. Avian influenza (influenza A H5N1): risk to human health. Jul 2024 [internet publication]. https://www.gov.uk/government/publications/avian-influenza-influenza-a-h5n1-risk-to-human-health

In light of the outbreak, the CDC has published interim guidelines for prevention, monitoring, and public health investigations.[37]Centers for Disease Control and Prevention. Highly pathogenic avian influenza A(H5N1) virus in animals: interim recommendations for prevention, monitoring, and public health investigations. Jun 2024 [internet publication]. https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html

Members of the public are advised to:

• Avoid close, long, or unprotected exposures to sick or dead animals, including wild birds, poultry, other domesticated birds, and other wild or domesticated animals (including cows).

• Avoid unprotected exposures to animal feces, bedding/litter, unpasteurized (raw) milk or cheeses, or materials that have been touched by, or closely exposed to, birds or other animals with suspected or confirmed H5N1 virus infection.

Clinicians are advised to consider the possibility of HPAI A(H5N1) virus infection in anyone showing signs or symptoms of acute respiratory illness who has a relevant exposure history.

• People are advised to monitor themselves for new respiratory illness symptoms, including conjunctivitis, for 10 days after their last exposure if they meet relevant epidemiologic criteria. Antiviral postexposure prophylaxis may be considered in certain people to prevent infection.

• Symptomatic people are advised to seek prompt medical care for diagnosis and treatment, and isolate themselves away from others.

The CDC recommends oseltamivir as the first-line treatment in both symptomatic outpatients and hospitalized patients.[38]Centers for Disease Control and Prevention. Interim guidance on the use of antiviral medications for treatment of human infections with novel influenza A viruses associated with severe human disease. Sep 2024 [internet publication]. https://www.cdc.gov/bird-flu/hcp/novel-av-treatment-guidance

Sporadic human cases of HPAI A(H5N1) infection have been reported since 1997, with a case fatality rate of more than 50% in reported cases. Most human infections have occurred after unprotected exposure to sick or dead infected poultry. There has been no evidence of sustained human-to-human transmission, and limited nonsustained human-to-human transmission has not been reported since 2007.

See Epidemiology

Original source of update