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

Health Update

TO: Healthcare Providers

Updated Guidance on Recommended Specimens for Human Avian Influenza A(H5N1) Testing

4/2/2025

Key Messages

This document provides updated Centers for Disease Control and Prevention (CDC) guidance on recommended specimens for human avian influenza A(H5N1) testing.  
In the prior instructions, persons with conjunctivitis who had conjunctival swab(s) collected, were also required to have respiratory specimens collected even if they had no other symptoms. It is no longer necessary to collect respiratory specimens from persons whose only symptom is conjunctivitis.
This document supersedes the guidance on recommended specimens to collect for human avian influenza A(H5N1) testing in the California Department of Public Health (CDPH) December 6, 2024 Evaluation and Testing for Human Avian Influenza A(H5N1) Infection.

Background

On March 20, 2025, CDC published updated instructions for use for the CDC Human Influenza Virus Real-Time RT-PCR Diagnostic Panel (CDC Flu rRT-PCR Dx Panel) Influenza A/H5 Subtyping Kit (VER 4).

In the prior instructions for use, persons with conjunctivitis who had conjunctival swab(s) collected, were also required to have respiratory specimens collected even if they had no other symptoms. It is no longer necessary to collect respiratory specimens from persons whose only symptom is conjunctivitis.

Specimens for Human Influenza A(H5N1)

If the CDC H5 subtyping assay* is used, conjunctival swabs alone may be tested in persons who have conjunctivitis and no other symptoms and a strong epidemiological reason to suspect H5N1 infection.

Persons with conjunctivitis and respiratory and/or non-specific symptoms (e.g., fever, headache), should continue to have conjunctival and respiratory specimens collected.

Persons without conjunctivitis but who have respiratory and/or non-specific symptoms (e.g., fever, headache), should continue to have respiratory specimens collected.

Respiratory specimens recommended by CDPH for H5 subtype testing:

Separate oropharyngeal and anterior nares swabs are preferred (combining both swabs into a single transport media tube is also acceptable).
Nasopharyngeal swabs are acceptable, but to date have had a lower yield for positive test results in cases than oropharyngeal or anterior nares swabs.

*Only public health laboratories in California are using the CDC H5 subtyping assay. Commercial and academic laboratories are using their own laboratory-developed H5 subtyping assays.