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State of California—Health and Human Services Agency
California Department of Public Health

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TO: Healthcare Providers and Clinical and Commercial Laboratories
Influenza A Testing Guidance: Enhanced Surveillance During the Summer Months

​​​Key Messages

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. 


The following activities are recommended to maintain awareness of influenza A subtypes circulating in California.  ​

Providers should: ​

  • Test for influenza (preferably with a RT-PCR) in patients with signs and symptoms of respiratory illness (with or without fever or conjunctivitis), especially if there is a history of potential exposure to avian influenza H5N1 (e.g., exposure to dairy cows, raw milk, wild birds, poultry, agricultural fair attendance). If subtyping is available, it should be performed. 

  • Providers should also be aware of CDC guidance regarding antiviral treatment and prophylaxis in the event of suspected influenza A (H5N1) human cases and exposures; these recommendations should be implemented in consultation with local public health departments.   

  • Test for influenza in patients with severe respiratory illness (i.e., hospitalized or ICU) irrespective of exposure history and arrange for subtyping of all influenza A positive specimens.  Please ensure the laboratory you use for influenza A testing is aware that influenza positive specimens that are not subtyped be submitted to the local public health laboratory. 

  • Report any suspected case of novel, avian, or variant influenza by calling the local health department immediately.  Reports should be made if novel or variant influenza is suspected based on symptoms and relevant exposure, or if an influenza A test is positive, but subtyping was attempted and did not identify a seasonal influenza A subtype (this includes unsubtypeable results). ​

Clinical and commercial laboratories should: 

  • Report any samples that are influenza A positive and for which subtyping was attempted but did not identify a seasonal influenza A subtype to the local health department and urgently direct these samples to a local public health laboratory for additional testing. 

  • During June through September 2024, submit influenza A positive samples not subtyped in clinical laboratories to local public health laboratories for influenza A subtyping. Continued collection of specimens for influenza testing and subtyping all influenza A positives over the summer is key to maintaining visibility of the influenza A subtypes circulating in the community, and for enhanced detection of novel and variant influenza cases.   



* Influenza A (H5N1) is sometimes also referred to as “highly pathogenic avian influenza (HPAI)” due to its devastating impacts in poultry.​