#19,381
In November of 2025, Washington State reported the first known human infection with avian H5N5; a diagnosis that was delayed - according to an MMWR report - by `early and repeated negative influenza test results from upper respiratory swab specimens'.
As we've previously discussed, it takes a certain amount of luck for novel flu infections to be detected, properly treated, and then reported to the CDC.
In the H5N5 case above, the patient died. In 2024, a Missouri patient was hospitalized with influenza A, and released, before being notified they had H5N1 (see Missouri DHSS: Human H5 bird flu case confirmed in Missouri). In both cases, numerous hospital workers (and others) were unknowingly exposed.
How many novel flu infections go undetected is unknown, although numerous studies suggest it happens more than we think (see JAMA Open: Asymptomatic Human Infections With Avian Influenza A(H5N1) Virus Confirmed by Molecular and Serologic Testing and MMWR: Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers).
No screening system can be expected to catch every case (and many mild cases simply won't seek medical care), but a standardized screening procedure can improve the chances.
Yesterday King County, Washington published updated guidance for screening for novel influenza, following last week's report of a dairy-exposure infection in Yakima county. This appears to be a condensed version of guidance published by the WA State Dept. of Health (Provider Alert: Testing and Subtyping for Avian Influenza) published on Oct 9th.
The emphasis here is on testing patients with ARI (Acute Respiratory Illness) with recent (past 10 days) epidemiologic risk factors (poultry/livestock exposure, raw dairy or animal products, known contact with a human case, etc.).
Today's guidance appears to back away from that, although the reason behind that isn't stated.
Based on the CDC's analysis of 72 human cases since 2024, however, it does appear that the vast majority of known cases had some kind of animal exposure.
I've reproduced the King County Guidance below, followed by a link to the WA State provider update. I'll have a postscript after the break.
October 20, 2026
Updated guidance for novel influenza screening and influenza subtyping
➜ This health advisory is also available in PDF format (223 KB)
Current situation
Highly pathogenic avian influenza (HPAI or bird flu) continues to circulate among wild birds and other animals in Washington. Although the risk to the general public remains low, clinicians should remain vigilant for possible avian influenza infections in patients with acute respiratory illness (ARI) and epidemiologic risk factors.
Guidance has changed for the 2026-27 influenza season, summarized below.
Actions requested
Identify
- Test all patients with ARI AND epidemiologic risk factors for influenza and obtain seasonal influenza subtyping for influenza A-positive specimens. Epidemiologic risk factors include the following within 10 days before symptom onset:
Test
- Close contact with sick or dead animals or their environments, especially birds, wildlife, livestock (including poultry), or domestic animals suspected of HPAI
- Consumption or handling of raw animal products or parts from potentially infected animals (e.g., raw cow milk or products made with it, raw meat-based pet food)
- Close contact (within 6 feet) to someone suspected or confirmed to have avian influenza
- Influenza A subtyping is NOT requested for patients without epidemiologic risk factors, including hospitalized patients. Note this is a change from previous recommendations.
- Avian influenza testing is available at WA DOH Public Health Laboratories (PHL) with prior approval from Public Health.
- If seasonal influenza A subtyping is not available through a clinical or commercial lab, the following specimens may be submitted directly to PHL without pre-approval:
Notify
- All influenza A specimens that result as "unsubtypeable" (influenza A positive test but seasonal influenza A subtype was negative or not identifiable)
- Specimens from hospitalized patients with risk factors for avian influenza, when seasonal influenza subtyping is not available
- Immediately report suspected and confirmed cases of novel influenza to Public Health at 206-296-4774, including patients with ARI and identified epidemiologic risk factors. Do not wait for lab confirmation before notifying us. The following are immediately notifiable:
- All suspected novel influenza, including avian influenza (influenza A H5 or others); a negative influenza PCR does not rule out avian influenza
- All influenza A specimens that result as "unsubtypeable"
CONTACT
Communicable Diseases Epidemiology and Immunization Section
401 5th Ave, Suite 1250
Seattle, WA 98104
Phone: 206-296-4774
TTY Relay: 711
Fax: 206-296-4803
- Provider Alert: Testing and Subtyping for Avian Influenza, WA State Dept. of Health
- Influenza Virus Testing at the Washington State Public Health Laboratories (PHL) including Novel Influenza and Fatal Influenza
- Influenza Specimen Collection and submission Instructions, WA State Dept. of Health
- Influenza Specimen Collection, CDC
- A(H5) Bird Flu: Current Situation | Bird Flu, CDC
In 2024 the ECDC issued guidance for member nations on Enhanced Influenza Surveillance to Detect Avian Influenza Virus Infections in the EU/EEA During the Inter-Seasonal Period., which cautioned:
Sentinel surveillance systems are important for the monitoring of respiratory viruses in the EU/EEA, but these systems are not designed and are not sufficiently sensitive to identify a newly emerging virus such as avian influenza in the general population early enough for the purpose of implementing control measures in a timely way.
A sobering reminder that, while we comfort ourselves with our current low number of human novel flu detections, we are probably missing some cases.