In order to maintain awareness of influenza A subtypes circulating in California:  

• Providers should report any suspected case of novel, avian, or variant influenza to local health department immediately, and should test for influenza in patients with respiratory illness and relevant animal exposures that could increase risk for influenza A (H5N1).  Providers should test severely ill patients irrespective of exposure history.   

• Clinical and commercial laboratories should submit influenza specimens to public health labs for subtyping.  Any clinical specimen for which subtyping is attempted and does not identify a seasonal subtype should be immediately reported to the local health department and urgently directed to a public health lab for further testing. ​​

The ongoing global outbreak of influenza A (H5N1)* in animals has caused the worst domestic poultry outbreak on record, with more than 90 million poultry affected in the U.S. to date. In March 2024, the first detection of influenza A (H5N1) in dairy cattle was reported in Texas.  Since then, there have been three mild human infections detected in dairy farm workers with exposure to infected dairy cattle in Texas (1) and Michigan (2). There has been no human-to human-transmission associated with these cases.   ​

Currently, influenza A (H5N1) is believed to pose a low risk to human health. The spread of avian influenza viruses from one infected person to a close contact is very rare, and when it has happened, it has only spread to a few people. However, because of the possibility that avian influenza viruses could gain the ability to spread easily between people, monitoring for human infection is important for public health. We believe the actions outlined below will enhance ongoing surveillance of novel influenza A in the U.S. 

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