#19,211
While reporting of HPAI H5 in dairy herds has slowed in 2026, we continue to see scattered outbreaks, with the most pronounced currently in the state of Idaho.
Similarly, we've not seen a human H5N1 case reporting in the United States in more than a year, but serological testing suggests some mild or asymptomatic cases may be flying under the radar.
Detection is highly dependent upon clinicians maintaining an elevated index of suspicion, and their willingness to order HPAI H5 specific tests. As we've seen often (see QJM: Avian Influenza in Humans: Virology, Transmission, and Clinical Priorities) the diagnosis is often missed - or at least delayed - even in hospitalized cases.
This past week, with the increase in outbreaks in Idaho's dairy herds, their Central District Health agency issued the following HAN Health Advisory:
Health Advisory: Consider Avian Influenza A (H5N1) in Patients with Dairy Cattle or Poultry Exposure
by Trent Young on June 16, 2026
HEALTH ALERT NETWORK – Health District 4
Advisory for Healthcare Providers: Consider Avian Influenza A (H5N1) in Patients with Dairy Cattle or Poultry Exposure
Key Messages
Local Situation: Avian Influenza A (H5N1) has been confirmed in over 80 Idaho dairy premises, including 12 in District 4 currently under ISDA quarantine.
Clinical Suspicion: Consider H5N1 infection in patients presenting with conjunctivitis or acute respiratory illness who report recent exposure to dairy cattle, sick poultry, or contaminated environments.
Report Immediately: Novel influenza A infections are immediately reportable. Contact CDH at 208-327-8625 to report suspected cases.
Occupational Risk: While the risk to the general public remains low, agricultural workers and others with direct animal exposure are at increased risk.
Background and Current Situation
Due to ongoing H5N1 detections in Idaho dairy herds and continued circulation in poultry, clinicians should consider H5N1 in patients with compatible illness and relevant exposure histories.
Since its detection in U.S. dairy cattle in March 2024, H5N1 has spread to more than 1,100 dairy herds across at least 20 states. There have been 71 reported human cases in the U.S. since 2024, most associated with dairy cattle exposure and direct contact with infected animals or contaminated milk. No human cases have been reported in Idaho. Most U.S. infections have been mild and characterized by conjunctivitis, although respiratory illness and severe disease can occur. There is no evidence of sustained person-to-person transmission.
Individuals at increased risk of exposure include:
- Dairy farm workers and milkers
- Veterinarians and animal health personnel
- Farm support staff (cleaning, transport, equipment handling)
- Household contacts of exposed workers
Clinical Presentation
Mild / Typical Illness:
Moderate to Severe Illness:
- Conjunctivitis (redness, irritation, discharge, foreign body sensation)
- Fever, cough, sore throat, rhinorrhea
- Fatigue, headache, myalgia, arthralgia
- Gastrointestinal symptoms
- Shortness of breath
- Altered mental status or seizures
- Pneumonia, ARDS, sepsis, multi-organ failure
Asymptomatic Testing:
Consider testing asymptomatic individuals with high-risk exposures (e.g., exposure to infected animals without recommended PPE or after a PPE breach). Collect respiratory and conjunctival specimens as recommended.
Laboratory Testing and Specimen Collection
- Idaho Bureau of Laboratories (IBL) Submission:
- Order Name: Influenza Subtyping
- Aliases: Flu A/B PCR, Flu A subtyping, H5N1, HPAI
- Commercial Lab Availability for Influenza A (H5):ARUP: Respiratory or conjunctival swabs
- LabCorp: Nasopharyngeal (NP) swabs only
- Quest: NP, nasal, OP, BAL, or conjunctival swabs
Standard Specimen Collection:
- Nasopharyngeal (NP) swab in one viral transport medium (VTM) tube
- Nasal and oropharyngeal (OP) swabs combined in a second VTM tube
- If conjunctivitis is present, collect a conjunctival swab in a separate VTM tube
- For severe illness, collect lower respiratory specimens (e.g., bronchoalveolar lavage or endotracheal aspirate) when feasible
- Rapid influenza diagnostic tests have limited sensitivity and should not be used to rule out H5N1 infection
Handling and Transport
- Coordinate specimen collection and submission with Central District Health before shipping.
- Store specimens:2–8°C for up to 72 hours, OR
- ≤ −20°C for longer storage (up to 30 days)
- If frozen:Do NOT thaw before testing
- Ship on dry ice for overnight delivery
- If refrigerated, transport promptly on cold packs
Antiviral Treatment and Prophylaxis
Do NOT delay treatment while awaiting results.
- Initiate oseltamivir 75 mg orally twice daily for 5 days for symptomatic adolescents and adults with suspected H5N1 infection. Refer to CDC guidance for pediatric dosing.
- Consider post-exposure prophylaxis for individuals with high-risk exposures, using recommended treatment dosing for 5 or 10 days, depending on the exposure scenario.
Central District Health Contact: 208-327-8625
ResourcesAvian Influenza (Bird Flu): Highly Pathogenic Avian Influenza A(H5N1) Virus: Interim Recommendations for Prevention, Monitoring, and Public Health. CDC.gov Updated December 26, 2024. Accessed January 09, 2026.
https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html
Emergency Use Instructions (EUI) Fact Sheet for Healthcare Providers: Oseltamivir for Treatment or Post-Exposure Prophylaxis of Novel Influenza A. February 18, 2025. https://www.cdc.gov/bird-flu/media/pdfs/2024/07/Oseltamivir-EUI-HCP_1.pdf
Avian Influenza (Bird Flu): Interim Guidance on Specimen Collection and Testing for Patients with Suspected Infection with Novel Influenza A Viruses Associated with Severe Disease or with the Potential to Cause Severe Disease in Humans. CDC .gov. Updated May 15, 2025. Accessed January 09, 2026. https://www.cdc.gov/bird-flu/php/severe-potential/index.html
While most known human H5 infections have been epidemiologically linked to a specific agricultural exposure (cows, chickens, wild birds, etc.), over the past 2 years we've seen a handful (U.S. x 4, Mexico x 3, Canada x 1) where the source of exposure remains unexplained.
Given the limits of surveillance and testing, it would not be terribly surprising if there are other cases in the community that have not been officially confirmed.
Particularly since some percentage of infections are asymptomatic or very mild (see MMWR: Serologic Evidence of Recent Infection with HPAI A(H5) Virus Among Dairy Workers).
Three years ago, in UK Novel Flu Surveillance: Quantifying TTD, we looked at a UKHSA report that it would likely take between 3 and 10 weeks before community spread of a novel flu virus would become apparent to authorities, after anywhere between a few dozen to a few thousand community infections
Anything we can do to shorten those delays could pay important dividends should HPAI take off.