H5N1 Highly Pathogenic Avian Influenza Update
(Updated 02/03/2025)
Background
In Spring 2022, a very large H5N1 avian influenza outbreak emerged in wild birds worldwide, including in North America. This outbreak continues and has affected many wild birds and poultry farms in Wisconsin and across the U.S.
On March 25, 2024, H5N1 avian influenza was detected in a dairy cow in Texas. Since that first detection, H5N1 avian influenza has been found in almost 1,000 cattle herds across 16 states.
On April 1, 2024, the Centers for Disease Control and Prevention (CDC) announced that H5N1 avian influenza had been detected in a person with exposure to dairy cattle in Texas. On December 18, 2024, the Wisconsin Department of Health Services (DHS) reported the first presumptive positive human case of highly pathogenic avian influenza (H5N1) in Wisconsin. Over 60 human cases of H5N1 have been detected in the U.S. in the past year, including one fatality.
Although CDC’s Risk Assessment for the general population remains LOW, additional precautions are being taken to enhance influenza surveillance across the country.
In Wisconsin, there have been no documented dairy cattle cases of avian influenza. People who have close contact with poultry or dairy cattle infected with H5N1 avian influenza are at increased risk for infection.
Highly Suspect Avian Influenza Cases
Requesting DPH approval for STAT testing of highly suspect avian influenza cases at the WSLH
Clinicians who suspect influenza virus infection in symptomatic patients with known exposure to the following should contact the Wisconsin Division of Public Health (DPH) to request rapid subtype-specific PCR testing at the WSLH –
- Ill or dying animals or their products
- Confirmed H5N1 positive flock/herd
- Person with a probable or confirmed case of H5N1
Normal business hours – call DPH at 608-266-5326.
After hours – call DPH at 608-258-0099 and ask for “the communicable disease epidemiologist on-call”.
NOTE: If the patient has bovine, swine or avian exposure that DOES NOT fit in with the categories listed above, DHS does NOT need to be notified, and the specimen should be sent in for influenza surveillance on the normal respiratory surveillance requisition form (See “Influenza A Surveillance” section below).
Avian Influenza Specimen Collection and Submission to WSLH
- Collect one nasopharyngeal (NP) swab and place in a tube of viral transport medium (VTM). (Note: For patients with conjunctivitis, additionally, obtain a conjunctival swab and place in a tube of VTM.)
- Use swabs with a Dacron or polyester tip with an aluminum or plastic shaft.
- For patients with lower respiratory illness, collect a lower respiratory tract specimen (e.g., BAL).
- Request an “Enhanced Surveillance” requisition form upon DPH approval by contacting WSLH Customer Service at 800-862-1013. Complete and submit a form for each submitted specimen.
- Please check “Avian Influenza Suspect” under reason for submission.
- Arrange transport so that specimens arrive at the WSLH within 24 hours of collection. Avian influenza suspects can be shipped Category B.
- Specimens can be transported to the WSLH by a carrier of your choice, or at NO COST when using Purple Mountain Solutions (PH: 800-990-9668).
- Please contact the WSLH Customer Service Department at 800-862-1013 if you have questions regarding laboratory testing.
Suspect Avian Influenza Testing at the WSLH
- Testing is usually completed within 24 hours of specimen receipt at the WSLH.
- There is no charge for avian influenza testing at the WSLH.
- Suspect avian influenza specimens that are submitted to the WSLH will first be tested with the CDC influenza A/influenza B/SARS-CoV-2 multiplex PCR assay.
- You will always receive a result for influenza A/influenza B/SARS-CoV-2 multiplex PCR.
- If a specimen is positive for influenza A, it will also be tested with a seasonal influenza A subtyping PCR and the influenza A – H5 specific subtyping PCR.
- You will receive a result for the seasonal influenza A seasonal subtyping PCR and the Influenza A/H5N1 subtyping PCR.
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Influenza A Surveillance
On January 16, 2025, the CDC issued a Health Alert Network (HAN) Health Advisory to clinicians and laboratories due to sporadic human infections with avian influenza A (H5N1) viruses amid high levels of seasonal influenza activity. CDC is recommending a shortened timeline for subtyping all influenza A specimens among hospitalized patients and increasing efforts at clinical laboratories to identify non-seasonal influenza.
Clinicians and laboratorians are reminded to test for influenza in patients with suspected influenza and, going forward, to now expedite the subtyping of influenza A-positive specimens from hospitalized patients, particularly those in an intensive care unit (ICU). This approach can help prevent delays in identifying human infections with avian influenza A (H5N1) viruses, supporting optimal patient care and timely infection control and case investigation.
In response to CDC HAN00520, the Wisconsin Department of Health Services (DHS) issued an information update on January 23, 2025 with Wisconsin-specific guidance.
Subtyping can be performed either at your clinical laboratory, a commercial laboratory, or a public health laboratory. The current guidelines for enhanced and accelerated influenza A surveillance specimens being requested by WSLH are detailed below.
What to Submit for Influenza A Surveillance:
Submit the following specimens to WSLH for subtyping. Do NOT batch specimens.
- All influenza A-related hospitalizations for patients admitted to the ICU (that haven’t already been subtyped).
- All positive influenza A specimens that are unsubtypeable (for example, positive for influenza A and negative for influenza A(H1) and A(H3), if subtyping was attempted).
- All positive influenza A specimens for patients with international travel history or reported exposure to any animal susceptible to infection with a novel influenza A (for example, bovine, swine, or poultry).
- If the patient has bovine, swine or avian exposure but DOES NOT fit the criteria for a Highly Suspect Avian Influenza Case (detailed above), this specimen should be sent in on the normal respiratory requisition form.
- DHS does NOT need to be notified.
- If the patient has bovine, swine or avian exposure but DOES NOT fit the criteria for a Highly Suspect Avian Influenza Case (detailed above), this specimen should be sent in on the normal respiratory requisition form.
- Three influenza-related hospitalizations per week (that haven’t already been subtyped) for each Wisconsin hospital.
- This is an increase from previous surveillance efforts when one specimen per week was requested.
- Please ensure that these specimens come from hospitalized patients.
Influenza A Surveillance Specimen Requirements:
Specimen Types and Volume
- All upper and lower respiratory specimens are acceptable for testing.
- It is preferred to receive a swab in VTM/UTM for testing, but an aliquot of specimen without the swab is also acceptable.
- Specimens should be positive for influenza A.
- WSLH requests at least 0.5 ml of specimen, but could run the test with as little as 250 ul without the ability to repeat the test or make a storage aliquot.
Storage and Transport
- Specimens must either be received at the WSLH within 72 hours of collection, or be frozen within 72 hours to be acceptable for influenza A subtyping.
- Send specimens on dry ice if previously frozen or if WSLH will not receive them within 72 hours of collection.
- Influenza A surveillance specimens may be sent via Purple Mountain. The dispatch phone number is 800-990-9668.
Influenza Surveillance Requisition Forms
- These influenza A surveillance specimens can be sent in using your normal “Respiratory Surveillance” requisition form.
- If you do not have a form, please contact WSLH customer service at 1-800-862-1013.
- Select “Influenza surveillance” or “Respiratory Surveillance” as the reason for submission. You do not need to specify “subtyping” on the form.
- It is critical that clinical laboratories ensure that requisition forms are filled out accurately and completely, including accurately indicating if a patient is hospitalized.
Influenza Surveillance Testing at WSLH
- Influenza A subtyping at the WSLH has a TAT of 2-3 days from specimen receipt.
- There is no fee for influenza subtyping of influenza A surveillance specimens.
- Influenza surveillance specimens that are submitted to the WSLH for testing will be tested with the CDC influenza A/influenza B/SARS-CoV-2 multiplex PCR assay.
- You will always receive results for the influenza A/influenza B/SARS-CoV-2 multiplex PCR.
- Specimens that are positive for influenza A will be also tested with a seasonal influenza A subtyping PCR.
- You will receive results for the seasonal influenza A subtyping PCR.
- Influenza A subtyping results may be received 1-3 days after influenza A/influenza B/SARS-CoV-2 multiplex PCR results are received.
Additional Information
Wisconsin Department of Health Services, Avian Influenza A Virus
CDC’s Flu Surveillance Systems Can Detect Avian Influenza A (H5N1) Virus Infections
CDC Avian Influenza guidance documents and information