Hawaii DOH Statement on Negative Testing Of Human Contacts to H5 Infected Flocks

Hawaii lies beneath the West Pacific Flyway

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Last week Hawaii - which until now had never reported HPAI H5 - discovered H5 in their wastewater system, and a few days later, detected an outbreak in captive wild birds on the island of Oahu.  

Over the past week the Hawaii state Department of Health has conducted an epidemiological investigation, including contact tracing and testing those who had high risk exposure to these birds.

Encouragingly, thus far they have found no evidence of human infection, although their investigation continues.  Overnight (EST) they released the following statement, which discusses both their investigation and the genotype (A3) of the virus. 

First their statement, then I'll return with some background on how different genotypes emerge, and how that can affect their behavior. 

DOH INVESTIGATING HUMAN CONTACTS TO INFECTED H5N1 FLOCKS-NO HUMANS IN HAWAIʻI TESTED POSITIVE FOR AVIAN INFLUENZA

Posted on Nov 21, 2024 in Newsroom

HONOLULU — The Hawaiʻi State Department of Health (DOH) is investigating human contacts to the flock infected with H5N1. No humans in Hawaiʻi have tested positive for avian influenza at this time.

To date, 54 individuals have been investigated for potential exposure. Of those, 34 were offered testing because of unprotected exposure (meaning without use of adequate personal protective equipment), to the infected birds within the past 10 days, or because they had developed respiratory symptoms within 10 days of contact with the birds.

Twenty-nine consented to testing, including 13 who had at least one symptom of respiratory infection and 16 who had no symptoms. All the individuals who would be considered to have very high-risk exposure to the infected birds, including prolonged direct contact with visibly sick, dying, or dead birds, consented to testing.

Testing involved collection of swabs from the nasopharynx, nose, throat, and/or conjunctiva that were tested by polymerase chain reaction (PCR) at the State Laboratories Division. Results for all 29 of those tested, including those with very high-risk exposure and/or symptoms, have come back negative for avian influenza. Two symptomatic individuals tested positive for common cold viruses. Investigation into potential exposures to individuals who interacted with ducks or geese at the Mililani Pet Fair on Nov. 2 is ongoing. At least four individuals whose only exposure was at the Mililani Pet Fair have been tested for avian influenza with all negative results. Additional investigation results will be shared as they become available.

DOH has worked with the U.S. Department of Defense to identify individuals with potential exposure. They have been tested and there are no confirmed cases.

The strain of avian influenza identified in the infected flock has been confirmed by the National Veterinary Services Laboratory as clade 2.3.4.4b, genotype A3. The A3 genotype was first identified in wild birds in Alaska in 2022. Identification of this genotype supports a theory of introduction of H5N1 to Hawaiʻi by migratory wild birds. This is a different genotype of the virus than the one that has infected dairy cows on the U.S. mainland and is also different from the genotype reported in a critically ill adolescent in British Columbia. It is unknown whether genotype A3 is likely to infect humans or other mammals.  

While initial human testing results are reassuring, DOH urges the public to continue to exercise caution. Avoid close contact with wild birds, and if you encounter birds that appear sick or have died, don’t approach them. Report sick or dead birds, especially if multiple or unusual, to the Department of Agriculture (808-483-7106 during Monday to Friday from 7:45 a.m. to 4:30 p.m. or 808-837-8092 during non-business hours and holidays).

Hawaiʻi residents who recently visited or worked on a farm in another state with known or suspected H5N1 animal infections should contact the Hawaiʻi Department of Health Disease Reporting Line 808-586-4586 for a telephone risk assessment.

As we've discussed often, H5N1 is not a single viral threat, but describes a large and growing array of similar viruses all of which carry an H5 HA gene and an N1 NA gene as their surface proteins.  There are other subtypes (with a different NA gene) - like H5N5 and H5N6 within the constellation of HPAI H5 viruses (see UK: HPAI H5N5 Rising) - along with numerous clades.

The H5N1 virus challenging much of the world today is clade 2.3.4.4b, but in Cambodia we've seen outbreaks from clade 2.3.2.1c, along with sporadic cases from India and Bangladesh of clade 2.3.2.1a. 

As a segmented virus with 8 largely interchangeable parts, the flu virus is like a viral LEGO (TM) set which allows for the creation of new subtypes - and within each subtype - variants called genotypes. 

New viruses can be created when two flu viruses inhabit the same host, allowing them to reassort into a hybrid.  Even when we limit the field to a specific subtype (like H5N1), and a specific sub-clade (like 2.3.4.4b), there can still be scores of genotypes due to reassortment.

Last fall researchers from several U.S. labs published a `snapshot' of H5N1's diversity in the United States in the months following its arrival in December of 2021. The found 3 different introductions of the virus, writing:

Unreassorted Eurasian genotypes A1 and A2 entered the Northeast Atlantic states, whereas a genetically distinct A3 genotype was detected in Alaska.

They further found that the virus rapidly reassorted with local wild bird avian influenza viruses generating six major (and numerous minor) genotypes.

Credit: Molecular detection and characterization of highly pathogenic H5N1 clade 2.3.4.4b avian influenza viruses among hunter-harvested wild birds provides evidence for three independent introductions into Alaska by Andrew M. Ramey a 1, Laura C. Scott a 1, Christina A. Ahlstrom a 1, Evan J. Buck a, Alison R. Williams b, Mia Kim Torchetti c, David E. Stallknecht d, Rebecca L. Poulson d

This reassortment process continues, and while more than 100 genotypes have been detected in North America over the past 3 years, in 2024 three new reassortments of note have emerged:

• B3.13 aka the `bovine' strain affecting dairy cattle in at least 15 states and infecting dozens of humans
• D1.1   a wild bird/poultry strain which has spilled over into > a dozen people in Washington State and a teenager in British Columbia
• D1.2  a wild bird/poultry strain which recently detected in poultry and 2 pigs in Oregon

In the 3 years prior to the emergence of these new genotypes, the United States only reported 1 H5N1 infection in a poultry culler in 2022.  Since March, we've seen well over 50 human confirmed infections, and it is likely many others have gone undetected.

While we might conclude that the older A3 genotype is less likely to infect humans based on past performance, we really don't know what it is that has changed in 2024 to increase spillovers, and whether those changes could impact older genotypes. 

Genotypes are still broad categories, and within each genotype there can be mutations - changes to specific amino acids at critical junctures - that can sometimes alter the virus's transmissibility, virulence, or its resistance to antivirals. 

Earlier this week we looked at the detection of the NA-S247N mutation in 3 poultry workers in Washington State - and while technically still genotype D1.1 - it is a significant variant.  It is not unusual to see dozens of mutations (most of which are benign) in a single isolate.

While we can hope there is some `species barrier' (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?) that will prevent H5 from ever becoming a pandemic strain, the virus has both time, and a growing array of genetic material with which to tinker.

But as we've seen so often, hope isn't much of a basis for a plan. 

USDA: California Announces 63 More Infected Dairy Herds (n=398) - More Poultry Outbreaks in 7 States

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On Monday, California announced another 41 infected cow herds, bringing their total to 335. Today, just 3 days later, that number has jumped again by 63, bringing them to 398 infected herds and the nation to 612. 

At this point more than 1/3rd of California's (roughly 1,100) herds have tested positive. What we don't know is how many herds that have been tested, have come back negative.

Once again, most states are not aggressively testing bulk milk, or cattle, for the virus. Only 4 non-affected states (Arkansas, Massachusetts, Oklahoma, and Pennsylvania) currently require precautionary bulk milk testing, and most states that have reported outbreaks do not have mandatory testing. 

As a result we continue to fly blind in regards to how many herds are affected, across how many states, and whether those numbers are increasing or declining. 

The USDA also updated the number of backyard and commercial poultry flocks that have been affected, with 13 outbreaks across 7 states (Alaska, California, Illinois, South Dakota, Minnesota, Washington, and Hawaii) added since Monday's update. 

Since `bird flu season' generally begins in mid October, we've only just begun this year's battle. 

Netherlands Raises Bird Flu Risk Assessment - Orders National Indoor Confinement of Poultry

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Last winter European nations saw a major reduction in HPAI H5 outbreaks (see ECDC/EFSA chart below), but over the past few weeks we've seen signs suggesting that this year may prove more active. 

Last weekend the Norway Veterinary Institute Reported their 1st Outbreak of HPAI H5N5 In Domesticated Birds, and earlier this month we looked at two outbreaks in the UK (H5N1 in Yorkshire, and H5N1 in Cornwall).

While this pales in comparison to what we've seen in Canada and the United States this fall (roughly 100 outbreaks combined), it is an uptick. And with the surge in the HPAI H5N5 subtype, concerns are growing. 

Yesterday, the Minster of Agriculture for the Netherlands announced a nationwide confinement order, due to a newly released (and elevated) risk assessment.  A reminder that HPAI is a global problem, and not just confirmed to the United States and Canada.

The full (translated) statement follows:

National confinement and screening obligation imposed due to bird flu outbreaks

News item | 20-11-2024 | 17:30


The Minister of Agriculture, Fisheries, Food Security and Nature has decided to introduce a nationwide obligation to keep animals indoors and to screen them off. This decision was taken after a new risk assessment by the Expert Group on Animal Diseases, which estimates the risk of bird flu outbreaks to be moderate to high.

Minister Wiersma of LVVN: “Implementing a national obligation to keep poultry indoors and screened off is a drastic measure that must be taken with due consideration. Also because of the effect on the animal welfare of poultry. Because the expert group on animal diseases has estimated the risk of bird flu outbreaks to be moderate to high, I have decided to take this measure. I realise that poultry owners with outdoor access and hobby owners are hit the hardest by this, but we must do our utmost to prevent more outbreaks. The safety of our animals is paramount.”

Risk assessment

On 18 November, bird flu was detected in Putten, Gelderland. On 20 November, another infection was detected close to the border with the Netherlands, namely in Kleve (Germany). Based on these 2 infections and all available information about outbreaks in other member states of the European Union, the risk of infection of a poultry farm in the whole of the Netherlands has been estimated as moderate to high (on 29 October this was low to moderate).

Obligation to confine and screen animals

The housing obligation applies to all commercially kept birds and the screening obligation applies to non-commercially kept risk birds (for example, chickens kept as a hobby). Pheasants and ratites (such as ostriches, rheas, emus and kiwis) are also risk birds, but for these birds the only exception is a screening obligation.

The obligation to screen and house birds is an effective preventive measure to prevent new infections, as it reduces the chance of contact between wild infected birds and captive birds.

Documents
Letter to Parliament introducing national confinement and screening obligation

Minister Wiersma (LVVN) informs the House of Representatives about the introduction of a national obligation to keep poultry indoors and shielded. ...

Parliamentary document: Letter to Parliament | 20-11-2024

Regulation of measures surveillance zone highly pathogenic avian influenza Kleve, Germany 2024

Regulation of the Minister of Agriculture, Fisheries, Food Security and Nature of 20 November 2024, no. WJZ/94346249, containing ...

Regulation | 20-11-2024

Regulation to introduce the obligation to keep animals indoors and to screen them off

Regulation of the Minister of Agriculture, Fisheries, Food Security and Nature, no. WJZ/94346915 amendment to the Regulation ...

Regulation | 20-11-2024

Pennsylvania To Require Precautionary Bulk Testing of Milk For H5N1

Pennsylvania - Credit Wikipedia

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While most states continue to rely on passive surveillance, and the willingness of farmers to report visibly sick cattle to agriculture officials, several states have ordered mandatory bulk milk testing in order to detect HPAI in dairy cows.  

Colorado famously did so over the summer, during their HPAI outbreak, and 3 other states currently without outbreaks (Arkansas, Massachusetts, and Oklahoma) have mandated regular bulk milk testing for the virus. 

Three weeks ago the USDA unveiled Plans for Enhanced Testing For H5N1 in Bulk Milk, but a timetable for doing so, and whether (or when) it would become mandatory, were not specified.  In early October, the FDA announced a Voluntary `Silo Study' To Blind-Test Raw Milk, but infected herds would not be identified.

Yesterday, Pennsylvania announced that no later than November 26th, every milk processor in Pennsylvania will be required to collect bi-weekly samples from each compartment of each milk tanker, and submit them for testing.

The press release from the State Agriculture department follows.

Pennsylvania Requires Precautionary Bulk Milk Testing at Processing Plants to Protect Dairy, Poultry Industries from Avian Influenza

November 20, 2024

At no cost to farmers, collective samples from milk tankers will aid early virus detection.

Surveillance testing will help prevent the spread of HPAI. No cases have been detected in Pennsylvania cattle to this point.

Harrisburg, PA – Today, Agriculture Secretary Russell Redding announced that Pennsylvania will now require precautionary bulk testing of milk for HPAI from Pennsylvania farms as an added measure to prevent the spread of avian influenza. No virus has been detected in Pennsylvania cattle, but cases continue to rise in other states.

The Pennsylvania Department of Agriculture is taking this preventative measure, at no cost to farmers, to pinpoint and contain the source of viral infections and prevent the spread of Influenza A, including highly pathogenic avian influenza (HPAI). Procedures are detailed in a quarantine order effective today. Several other states have implemented mandatory bulk testing of milk to reduce the spread of HPAI, including California, Colorado, Michigan, and Oklahoma.

This testing plan was developed in close consultation with dairy and poultry farmers to minimize the impact on their operations.

The measure is announced as more than 217 new cases in three states have been confirmed in dairy cattle in the last 30 days. Not typically fatal in dairy cattle, HPAI can severely affect milk production, lead to serious illness in some cows, and substantially strain farm operations. The virus is fatal in poultry.

“Taking this proactive step will ensure that we can protect our cattle, poultry, and farmworkers,” Secretary Redding said. “We are taking this step after careful consideration, in consultation with dairy and poultry farmers, and after voluntary testing was not adequate to get samples necessary for detection and prevention. Pennsylvania’s large number of farms with both dairy cattle and poultry present unique risks that demand extra vigilance.”

Milk samples will be collected from bulk milk tank trucks transporting milk from Pennsylvania farms to processing plants. If the receiving processing plant is in Pennsylvania, the sample will be collected at the plant by the processor. If the processing plant is outside Pennsylvania, the sample will be collected by the shipper, whether the shipper is an individual farmer or milk cooperative handling milk on behalf of farmers. Samples must have been taken by trained, certified personnel and submitted to a Pennsylvania Animal Diagnostic Laboratory System lab within 48 hours of collection.

Samples will be tested for HPAI. If the virus is detected, it will trigger further investigation to identify the source. Special quarantine measures will be established to contain and eliminate the virus at the source.

Pennsylvania joins only three states without an active HPAI outbreak – Arkansas, Massachusetts, and Oklahoma – in requiring precautionary testing at the processor level. Milk that has been pasteurized is safe to drink. Pasteurization destroys the virus. This measure will help ensure an adequate supply of milk in the marketplace.

This new measure adds to requirements already in place to help prevent the spread of HPAI. In April 2024, Pennsylvania led the nation in issuing a Quarantine Order requiring testing of dairy cattle entering the state when HPAI was first detected in herds in other states. Pennsylvania’s strategic move was soon followed by USDA and other states.

(Continue . . . )

While this is obviously a step in the right direction, in far too many states, `Don't test, don't tell' remains the preferred course of action.  HPAI is viewed as primarily an economic - and political - problem; one that few are willing to address directly.

As a result, after 8 months and 550 infected herds detected across 15 states, we've no idea how big the problem really is, and whether it is continuing to spread. 

Preprint: Enhanced Encephalitic Tropism of Bovine H5N1 Compared to the Vietnam H5N1 Isolate in Mice

 

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Although seasonal flu can occasionally cause neurological symptoms (see 2018's Neuroinfluenza: A Review Of Recently Published Studies) it is relatively rare phenomenon, and usually only results in mild, and transient symptoms. 

The exact mechanisms behind these neurological manifestations are largely unknown, as seasonal flu viruses are generally regarded as being non-neurotropic.

Some researchers have posited that neurological symptoms may be due to neuroinflammation induced by the host's immune response. Regardless of the mechanism, we've seen seen evidence that some influenza viruses - particularly novel flu types - can be more neuroaffective than others.

Fifteen years ago H5N1 was considered primarily a respiratory disease, but in 2009 a PNAS study (link below) found that the H5N1 virus was highly neurotropic in lab mice, and in the words of the authors `could initiate CNS disorders of protein aggregation including Parkinson's and Alzheimer's diseases’.

Highly pathogenic H5N1 influenza virus can enter the central nervous system and induce neuroinflammation and neurodegeneration

In early 2014 we saw Alberta Canada Report a Fatal (Imported) H5N1 Infection, in a nurse who'd traveled to China for the holidays and succumbed to the virus shortly after her return.  This was Canada's 1st H5N1 infection, and in the following year we saw a study which described her infection as `neurotropic'. 

CJ ID & MM: Case Study Of A Neurotropic H5N1 Infection - Canada

The patient presented with `. . . pleuritic chest and abdominal pain . . . , this was followed by headache, confusion and, ultimately, respiratory failure, coma and death.' After reviewing MRI imaging and histological analyses, the authors wrote: `These reports suggest the H5N1 virus is becoming more neurologically virulent and adapting to mammals'.

Also in 2015 a Scientific Reports study on the genetics of the H5N1 clade 2.3.2.1c virus - Highly Pathogenic Avian Influenza A(H5N1) Virus Struck Migratory Birds in China in 2015 – the authors warned of its neurotropic effects, and that it could pose a ` . . . significant threat to humans if these viruses develop the ability to bind human-type receptors more effectively.'

While clinical details of many H5Nx human infections go unpublished, in 2022, in Clinical Features of the First Critical Case of Acute Encephalitis Caused by Avian Influenza A (H5N6) Virus, we learned of the severe neurological impact of the virus on a 6 year-old girl in China.

While certainly not the typical presentation of H5Nx infection in humans, the authors wrote:

In view of the fact that the clinical manifestations of this novel H5N6 reassortant are acute encephalitis, rather than previous respiratory symptoms, once these reassortants obtained the ability of human-to-human transmission through reassortment or mutations, it will bring great health threat for human.

 Over the past few years we've seen numerous reports of mammals infected with the 2.3.4.4b subclade of H5Nx experiencing severe, and often fatal, neurological manifestations.  Often, cats and other small mammals were initially suspected being rabid, only to test positive for H5Nx.

Just over a year ago, in Cell: The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans, we looked at a review that looked at the history, and recent trends, of neuropathogenesis of avian H5 in mammals.

All of which brings us to a preprint, published yesterday by researchers at NIAID (NIH), which compares the neurotropism of a 20 year-old strain of H5N1 collected from Vietnam to a recent isolate of the `bovine' B3.13 genotype of H5N1. 

What they find is the `modern' version of H5N1 is far more neurotropic in lab animals (mice) than its ancestral strains.  

The authors do point out that `Importantly, the findings in this study appear to be mouse specific and likely not representative of what will occur in humans, as thus far there is no evidence of CNS infection in contemporary H5N1 patients.'

But it is further evidence that the H5N1 viruses circulating today are different from those that emerged two decades ago in Southeast Asia, and they continue to evolve in unpredictable ways.   

First the link and abstract from the 38-page preprint, then I'll return with a bit more.

Enhanced encephalitic tropism of bovine H5N1 compared to the Vietnam H5N1 isolate in mice

Kerry Goldin,  Sarah van Tol, Randall C Johnson, Reshma Koolaparambil Mukesh, Shane Gallogly, Jonathan E Schulz, Greg Saturday, Kwe Claude Yinda, Vincent J Munster, Emmie de Wit, Neeltje van Doremalen
doi: https://doi.org/10.1101/2024.11.19.624162

          PDF 

Abstract

In recent years, the landscape of highly pathogenic avian influenza (HPAI) virus infections has shifted, as evidenced by an increase in infections among mammals. This includes the recent circulation of H5N1 in dairy cattle herds in the USA and a rise in associated human cases.

In this study, we investigated differences in tissue tropism of two HPAI H5N1 strains, the isolate A/Vietnam/1203/2004 (VN1203) isolated from a fatal human case in 2004 and the bovine isolate A/Bovine/Ohio/B24osu-342/2024 (Bov342) isolated in 2024, in C57BL/6J mice.

Infection with either HPAI H5N1 isolate was uniformly lethal in mice. However, tissue tropism differed significantly: while VN1203 replication was largely restricted to the respiratory tract, Bov342 successfully replicated in the respiratory tract as well as various regions of the brain.

Bov342-challenged animals exhibited clinical signs consistent with central nervous system (CNS) infection, and infectious virus was detected in brain tissue.

Correspondingly, cytokine profiles in the brain differed significantly between the isolates. Notably, in addition to abundant evidence of CNS infection in Bov342-challenged mice via immunohistochemistry, sporadic intranuclear and intracytoplasmic immunoreactivity was observed in other tissues in the head, including the choroid plexus, retina, and inner ear.

This study demonstrates that while both HPAI H5N1 isolates are uniformly lethal in C57BL/6J mice upon aerosol exposure, significant differences exist in tissue tropism, with Bov342 resulting in respiratory disease as well as increased neurotropism and inflammation in the brain and nasal turbinates compared to VN1203, which predominantly induces respiratory disease.

         (Continue . . . )

While there are still more questions than answers, over the years we've looked at numerous studies (some more compelling than others) linking severe and/or repeated viral infections (including flu) to a variety of neurological diagnoses later in life. 

In 2011 a study by Boise State biology professor Troy Rohn  appeared in PLOS ONE , which unexpectedly found immunohistochemical evidence of prior influenza A infection in the post-mortem brain tissues of 12 Parkinson’s patients they tested.

Immunolocalization of Influenza A Virus and Markers of Inflammation in the Human Parkinson's Disease Brain

Troy T. Rohn*, Lindsey W. Catlin

The following year, in Revisiting The Influenza-Parkinson’s Link, we looked at another study, conducted by the University of British Columbia, that found a linkage between a past history of severe bouts of influenza and the likelihood of developing Parkinson’s disease later in life.

According to their research, a severe bout of influenza doubled a person’s chances of developing the neurological condition (Severe flu increases risk of Parkinson's: UBC research).

None of this is conclusive, but it does raise serious questions. 

As did a study published last year in Neuron: Virus Exposure and Neurodegenerative Disease Risk Across National Biobanks, which found statistical linkage between viral illnesses and developing neurodegenerative diseases later in life. 

Whenever we talk about long-term sequelae from influenza, the mysterious decade-long epidemic of Encephalitis Lethargica (EL) that followed the 1918 pandemic always comes to mind.

It is estimated that between 1 and 5 million people were affected with severe Parkinson's-like symptoms.  While some scientists have suggested they may have been linked to the pandemic virus, others have pointed to a post-streptococcal immune response, or believe it was an aberrant autoimmune response, and dismiss the link with the 1918 pandemic.

The cause remains a mystery.

Throughout history, there have been reports of similar outbreaks, including febris comatosa which sparked a severe epidemic in London between 1673 and 1675, and in the wake of the 1889–1890 influenza pandemic, a severe wave of somnolent illnesses (nicknamed the "Nona") appeared.

And more recently, we've seen evidence that SARS-CoV-2 infection can produce persistent neurological manifestations (see CMAJ: Even Mild COVID-19 May Have Long-term Brain Impacts).

While the mild presentation of H5N1 in the United States thus far is reassuring, these viruses continue to mutate and evolve, and what we say about them today may not hold true tomorrow. 

Because with influenza viruses, the only constant is change. 

California Dept Public Health: Investigating Presumed Positive H5 Infection In A Child

 

Alameda County - Credit Wikipedia

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While it hasn't appeared on the California PHD website yet, that agency emailed the following statement out shortly before noon EST today.  It described a presumed positive H5 case in a child in Alameda County with mild respiratory symptoms. 

Samples have been sent to the CDC for confirmation. Thus far the CDC has not offered a statement.

Note: The subtype is not mentioned in this statement, but I'm assuming it is H5. 

FOR IMMEDIATE RELEASE 

November 19, 2024 

NR24-037 

Contact: media@cdph.ca.gov 

State Reports Single, Possible Case of Bird Flu Virus in Child with Mild Symptoms

No person-to-person spread of the virus has been detected or is suspected; Risk to public remains low

What You Need to Know: California has identified a possible bird flu case in a child who has had mild respiratory symptoms and is recovering at home. Human infections with bird flu viruses are rare, and no person-to-person spread has been detected in California or the United States. 

SACRAMENTO – California has identified a possible bird flu case in a child in Alameda County who was tested for mild upper respiratory symptoms. The child, who has been treated, is recovering at home. They had no known contact with an infected animal, but public health experts are investigating a possible exposure to wild birds.

The California Department of Public Health (CDPH) is working with local public health officials and the Centers for Disease Control and Prevention (CDC) to investigate the cause of the initial positive test in the child. The positive test showed a low-level detection of the virus, indicating the child was not likely infectious to others. Repeat bird flu testing on the child four days later was negative, and additional testing shows the child was also positive for respiratory viruses that could be the cause of their cold and flu symptoms.

The test specimens are being sent to CDC for confirmatory testing.

Family Members Tested Negative

No person-to-person spread of the virus has been detected or is suspected. Due to mild respiratory symptoms, all close family members of the child were tested – and all are negative for bird flu and not suspected of having the virus at all. Family members were also confirmed to have the same, more common respiratory viruses as the child. They are also being treated with preventive medication.

Additional Contacts Involved, No Indication of Larger Outbreak 

Out of an abundance of caution, other individuals who had contact with the child are being notified and offered preventive treatment and testing. Public health officials are aware that the child attended daycare with mild symptoms before the child’s test was reported as a possible bird flu infection. Local public health officials have reached out to potentially exposed caregivers and families to conduct health checks for symptoms and offer connections to preventive treatment and testing if they develop symptoms.

“It’s natural for people to be concerned, and we want to reinforce for parents, caregivers and families that based on the information and data we have, we don’t think the child was infectious – and no human-to-human spread of bird flu has been documented in any country for more than 15 years,” said CDPH Director and State Public Health Officer Dr. Tomás Aragón.

Bird Flu in Humans is Rare

Human infections with bird flu viruses are rare, and no person-to-person spread has been detected in California or the United States. In the rare cases where bird flu has spread from one person to another, it has never spread beyond a few close contacts.

Limited and sporadic human infections with bird flu where there is not clear route of exposure or infection are expected and have occurred in the past and during the outbreak public health officials have been monitoring since 2022. Regardless, public health surveillance and investigations of such cases will continue at the local, state and federal levels to monitor for any concerning changes.

People Working with Infected Animals are at Higher Risk 

People who have contact with infected dairy cows, poultry, or wildlife have a greater chance of getting bird flu, which can happen if the virus gets into a person’s eyes, nose, mouth, or is inhaled. As a general precaution, whenever possible people should avoid direct contact with sick or dead wild birds, poultry, and other animals and observe them only from a distance.

Since early October, California has reported 26 confirmed human cases of bird flu, all following direct contact with infected dairy cows. To date, all have reported mild symptoms (primarily eye infections), and none have been hospitalized. Because bird flu viruses can change and gain the ability to spread more easily between people, public health officials have provided preventive measures and are monitoring animal and human infections carefully.

CDPH has been closely monitoring the bird flu situation in both animals and humans since the state's first detection in poultry in 2022. To protect public health, and especially workers who may be exposed to infected animals, CDPH encourages those who work with infected dairy cows, raw milk, or infected poultry to use protective gear. Individuals who have symptoms or a significant exposure (such as raw milk splashing into the eye) should get tested quickly and treatment. In humans, bird flu symptoms include eye redness or discharge, cough, sore throat, runny or stuffy nose, diarrhea, vomiting, muscle or body aches, headaches, fatigue, trouble breathing, and fever.

Public health experts also encourage farm workers to get a flu shot this year. While a seasonal flu shot doesn’t stop bird flu, it protects against severe illness from seasonal flu and reduces the chance of human and bird flu viruses mixing and turning into new viruses that can spread more easily or be more severe.

Pasteurized Milk Products are Safe to Consume

Pasteurized milk and dairy products are safe to consume.  Drinking raw milk or eating raw milk products could be dangerous. Reduce your risk by choosing pasteurized milk and dairy foods like cheese and yogurt. Pasteurization, the process of heating milk to specific temperatures for certain times, inactivates the bird flu virus and harmful germs that can be found in raw milk.

For the latest information on the national bird flu response, see CDC's Bird Flu Response Update.