Colorado State Health Officials Identify Human Case of Avian Flu Amid Multi-State Outbreak


Denver (July 3, 2024) — In a collaborative effort involving the Colorado Department of Public Health and Environment (CDPHE), the Centers for Disease Control and Prevention (CDC), and the Colorado Department of Agriculture (CDA), health officials have confirmed a human case of avian influenza H5 infection. This case is part of a broader, multi-state outbreak of the virus that has significantly impacted dairy cattle populations.

The individual affected is an adult male who presented with mild symptoms, specifically conjunctivitis (commonly known as pink eye). Upon reporting his condition to state health authorities, he was tested for influenza at the State Public Health Laboratory. The samples were subsequently forwarded to the CDC for further analysis, which confirmed the presence of avian flu. Following standard CDC guidelines, the individual was treated with the antiviral medication oseltamivir and has since made a full recovery. He was employed at a dairy farm in northeast Colorado, where he had direct exposure to dairy cattle infected with avian flu. To maintain patient confidentiality, no additional personal details are being disclosed.

“Our partnership with the Colorado Department of Agriculture has been crucial in disseminating information to dairy farmers across the state,” stated Jill Hunsaker Ryan, executive director of CDPHE. “Coloradans should feel confident that the state is doing everything possible to mitigate the virus.”

Public health experts emphasize that it remains safe to consume pasteurized milk and properly handled and cooked dairy, beef, and poultry products in the United States. Proper handling and cooking practices effectively eliminate bacteria and viruses, including avian flu viruses. This was reaffirmed by a recent study released by the FDA and USDA, which highlighted the safety of the commercial milk supply.

“The risk to most people remains low. Avian flu viruses are currently spreading among animals, but they are not adapted to spread from person to person. Right now, the most important thing to know is that people who have regular exposure to infected animals are at increased risk of infection and should take precautions when they have contact with sick animals,” said Dr. Rachel Herlihy, state epidemiologist at CDPHE.

Health officials advise that Coloradans avoid touching sick or dead animals. If handling such animals is unavoidable, individuals should wear recommended personal protective equipment, including an N95 respirator, eye protection, and gloves. Thorough hand washing with soap and water is recommended after handling animals; if soap and water are not available, an alcohol-based hand sanitizer should be used.

Multi-State Outbreak and Historical Context

The current multi-state outbreak of avian influenza in dairy cattle, identified in the United States in March 2024, has seen three other human cases nationally. The last recorded human case of H5N1 in Colorado occurred in 2022, involving an individual exposed to infected poultry. This recent case underscores the ongoing threat of zoonotic diseases and the need for vigilant monitoring and response efforts.

“We continue to work closely with the Colorado Department of Agriculture, local public health agencies, and CDC as we monitor this virus to protect all Coloradans,” said Scott Bookman, senior director of public health readiness and response at CDPHE. “While it’s rare for people to become infected with avian flu viruses, direct exposure to infected animals increases that risk.”

Individuals working with potentially infected dairy cows who experience symptoms are urged to contact CDPHE at 303-692-2700 (or 303-370-9395 after business hours) for assistance with flu testing and medication. More comprehensive information about avian flu in humans can be found on the CDPHE website.

State Response and Regulatory Measures

The Colorado Department of Agriculture has been actively responding to the highly pathogenic avian influenza (HPAI) outbreak since 2022. In coordination with state and federal partners, including CDPHE and the U.S. Department of Agriculture, CDA has been confirming and addressing cases of avian flu. The disease is reportable in Colorado, necessitating notification to the State Veterinarian’s Office.

CDA has also implemented an Emergency Rule mandating the testing of lactating dairy cattle moving interstate. This measure aims to prevent the spread of HPAI and protect both animal and public health. Detailed information about CDA’s response efforts can be accessed on their official website.

The Broader Impact of Avian Influenza

Avian influenza, commonly known as bird flu, is a contagious viral infection that primarily affects birds but can also infect humans and other animals. The H5N1 strain, which is highly pathogenic, has caused significant outbreaks in poultry populations globally, leading to substantial economic losses and public health concerns.

Historically, avian flu outbreaks have necessitated the culling of millions of birds to control the spread of the virus. These measures, while effective in limiting transmission, have profound economic impacts on the agriculture sector. Additionally, the potential for avian flu viruses to mutate and adapt to human hosts poses a serious pandemic threat.

Global and National Trends

Globally, avian influenza remains a persistent threat with sporadic outbreaks reported in various regions. The World Health Organization (WHO) closely monitors these outbreaks, providing guidelines and coordinating international responses to manage and mitigate the risks associated with the virus.

In the United States, the USDA Animal and Plant Health Inspection Service (APHIS) plays a crucial role in managing avian flu outbreaks. APHIS conducts surveillance, enforces biosecurity measures, and works with state agencies to control and eradicate the virus in affected poultry populations.

Public Health and Safety Measures

Effective management of avian influenza outbreaks involves a multi-faceted approach, including surveillance, biosecurity, vaccination, and public awareness campaigns. Surveillance programs are essential for early detection and rapid response to outbreaks. These programs involve monitoring bird populations, both domestic and wild, for signs of illness and conducting regular testing.

Biosecurity measures are critical in preventing the introduction and spread of avian influenza in poultry farms. These measures include controlling access to farms, ensuring proper sanitation, and implementing strict protocols for handling and disposing of infected animals.

Vaccination of poultry is another tool used to control avian influenza. While not always feasible or necessary in all situations, vaccination can help reduce the severity of outbreaks and protect at-risk bird populations.

Public awareness campaigns are vital for educating both the agricultural community and the general public about the risks associated with avian influenza and the importance of preventive measures. These campaigns often emphasize the need for proper handling and cooking of poultry products, as well as the importance of reporting sick or dead birds to authorities.

Advances in Research and Technology

Ongoing research and technological advancements are crucial in the fight against avian influenza. Scientists are continually studying the virus to better understand its transmission dynamics, pathogenicity, and potential for human adaptation. This research informs the development of more effective vaccines, antiviral treatments, and diagnostic tools.

One area of significant progress is in the field of genomics. By sequencing the genomes of avian influenza viruses, researchers can track mutations and identify genetic markers associated with increased virulence or resistance to antiviral drugs. This information is critical for developing targeted interventions and for monitoring the evolution of the virus.

International Collaboration and Coordination

Given the global nature of avian influenza, international collaboration and coordination are essential for effective management and control of the virus. Organizations such as the WHO, the Food and Agriculture Organization (FAO), and the World Organisation for Animal Health (OIE) play pivotal roles in facilitating cooperation among countries.

These organizations provide guidelines, technical support, and resources to help countries strengthen their avian influenza surveillance and response capacities. They also facilitate the sharing of information and best practices, enabling countries to learn from each other’s experiences and improve their own strategies.

The Role of Public Health Infrastructure

A robust public health infrastructure is fundamental to managing zoonotic diseases like avian influenza. This infrastructure includes well-equipped laboratories, trained personnel, and effective communication networks. It also requires strong partnerships between public health agencies, veterinary services, and the agricultural sector.

In Colorado, the coordinated efforts of CDPHE, CDA, and the CDC exemplify the importance of such partnerships. By working together, these agencies can ensure a comprehensive and effective response to avian influenza outbreaks, protecting both public and animal health.

Future Directions and Challenges

Despite significant progress in managing avian influenza, several challenges remain. One of the primary challenges is the ongoing risk of virus mutation and the potential emergence of new, more virulent strains. This underscores the need for continued vigilance and adaptability in surveillance and response efforts.

Another challenge is ensuring global equity in access to resources and support for managing avian influenza. Developing countries often face greater challenges due to limited infrastructure and resources. International efforts must continue to focus on providing support and capacity-building to these countries to ensure a global, coordinated response to avian influenza.

Global Officials Identify Human Cases of Avian Flu Amid Multi-State Outbreak of H5N1

In recent months, the Centers for Disease Control and Prevention (CDC), in coordination with global health authorities, has identified several human cases of avian influenza H5N1 amid a multi-state outbreak affecting dairy cattle and other animals. This outbreak, first detected in March 2024, marks a significant public health concern due to the virus’s zoonotic potential—its ability to transmit from animals to humans.

Overview of the Outbreak

The H5N1 avian influenza virus, a highly pathogenic strain, has been circulating among wild birds and domestic poultry in the United States since 2022. However, the recent detection in dairy cattle in states such as Texas and Kansas is particularly notable. This outbreak represents the first known cases of H5N1 transmission from cattle to humans. Globally, H5N1 is part of the Gs/GD lineage, clade, which has been prevalent in avian populations.

Human Cases and Transmission

To date, there have been several human cases linked to this outbreak. The first reported human infection in the United States during this outbreak occurred on April 1, 2024, in Texas, involving a dairy farm worker. Subsequent cases have been identified, including one in Michigan on May 22, 2024. These cases highlight the virus’s ability to infect humans through direct contact with infected animals or contaminated environments.

Public Health Response and Surveillance

The CDC and state health departments have implemented extensive surveillance and public health measures to monitor and control the outbreak. This includes testing individuals who have had direct contact with infected animals and conducting seroprevalence studies to assess the extent of asymptomatic infections among exposed populations. Over 780 people have been monitored, and at least 53 individuals who developed flu-like symptoms have been tested for H5N1.

Laboratory Findings and Virus Adaptation

Laboratory studies have focused on understanding the virus’s receptor binding properties. The hemagglutinin (HA) protein of the virus identified in Texas has shown a preference for avian-type receptors and not human-type receptors, indicating that the virus has not yet adapted to easily infect humans. This is a critical finding as it suggests that while the risk of human-to-human transmission remains low, the potential for the virus to adapt necessitates ongoing vigilance.

Preventive Measures and Recommendations

Health authorities have issued several recommendations to mitigate the risk of H5N1 infection:

  • Avoid Contact with Infected Animals: People should avoid exposure to sick or dead animals, including wild birds, poultry, and livestock.
  • Use of Personal Protective Equipment (PPE): Workers in contact with potentially infected animals should wear appropriate PPE, including N95 respirators, gloves, and eye protection.
  • Safe Food Practices: It is essential to avoid consuming raw or undercooked animal products, such as unpasteurized milk and raw cheese, from infected animals.
  • Public Awareness: Outreach programs have been launched to educate farm workers and the general public about the risks and preventive measures, including multilingual resources to ensure broad accessibility.

Global Context and Historical Perspective

Since the initial detection of H5N1 in humans in 1997, there have been sporadic cases globally, with a high case fatality rate. From 2003 to April 2024, 889 human cases and 463 deaths were reported across 23 countries. The most recent global cases before the current U.S. outbreak were reported in Vietnam in March 2024.

The identification of human cases of H5N1 amid a multi-state outbreak underscores the importance of robust surveillance and preventive measures to control zoonotic diseases. The coordinated efforts of the CDC, state health departments, and international health organizations are crucial in monitoring the outbreak, providing timely information, and implementing effective public health responses. Ongoing research and surveillance will be essential to mitigate the risk of further transmission and ensure public health safety.

For more detailed information and updates, refer to the CDC and WHO websites, which provide comprehensive resources and guidance on avian influenza and related public health measures.

able: Worldwide Human Cases of Avian Influenza H5N1 (2024)

RegionDate of First Detection (2024)Number of Human CasesOutbreak SourceSymptoms ReportedPublic Health ResponsePreventive MeasuresReferences
United StatesMarch 20243 confirmed casesDairy cattle (Texas, Kansas)Conjunctivitis, mild respiratory symptomsSurveillance of exposed individuals, seroprevalence studies, testing symptomatic individualsAvoid contact with sick/dead animals, use PPE, safe food practicesCDC, WHO
VietnamMarch 20241 confirmed casePoultrySevere respiratory symptomsIsolation of cases, testing of contacts, public awareness campaignsAvoid contact with poultry, use PPE, vaccination of poultryWHO
ChinaApril 20242 confirmed casesWild birdsSevere respiratory symptoms, gastrointestinal symptomsMonitoring of poultry markets, testing of exposed individuals, public health advisoriesAvoid contact with wild birds, use PPE, vaccination of poultryWHO
EgyptFebruary 20241 confirmed caseDomestic poultrySevere respiratory symptomsQuarantine of affected areas, testing of exposed individuals, public awarenessAvoid contact with poultry, use PPE, vaccination of poultryWHO
IndiaMay 20241 confirmed caseDomestic poultryMild respiratory symptomsSurveillance of poultry farms, testing symptomatic individuals, public health campaignsAvoid contact with poultry, use PPE, vaccination of poultryWHO
IndonesiaApril 20241 confirmed casePoultrySevere respiratory symptomsTesting of poultry, isolation of cases, public health notificationsAvoid contact with poultry, use PPE, vaccination of poultryWHO

Summary of Public Health Responses and Recommendations

United States

  • Surveillance: Active monitoring of over 780 individuals exposed to infected animals, testing 53 symptomatic individuals.
  • Public Health Campaigns: Outreach through social media, fact sheets in multiple languages.
  • Research and Laboratory Testing: Genome sequencing, receptor binding studies indicating the virus is not well-adapted to human transmission.
  • Recommendations: Avoid contact with sick/dead animals, use of PPE, avoid raw milk and undercooked animal products​ .


  • Surveillance: Isolation of confirmed cases, extensive contact tracing, and testing.
  • Public Health Campaigns: Informing the public about risks associated with poultry contact.
  • Vaccination: Efforts to vaccinate poultry to prevent further spread.
  • Recommendations: Similar to US recommendations with emphasis on avoiding poultry contact​ ​.


  • Monitoring: Active monitoring in poultry markets, testing of birds and humans.
  • Public Health Campaigns: Awareness programs in regions with detected cases.
  • Vaccination: Ongoing vaccination efforts in poultry.
  • Recommendations: Enhanced focus on avoiding contact with wild birds, safe handling practices​ ​.


  • Quarantine and Testing: Quarantine measures in affected areas, rigorous testing protocols.
  • Public Awareness: Campaigns to educate the public on safe poultry practices.
  • Vaccination: Targeted vaccination programs for poultry.
  • Recommendations: Avoid contact with poultry, use of PPE, proper food handling​ ​.


  • Surveillance and Testing: Active surveillance of poultry farms, testing of symptomatic individuals.
  • Public Health Campaigns: Education on safe poultry practices.
  • Vaccination: Ongoing efforts to vaccinate poultry to control the spread.
  • Recommendations: Similar to other regions, focusing on safe contact and food practices​ ​.


  • Monitoring and Isolation: Testing of poultry, isolation of human cases to prevent spread.
  • Public Awareness: Information campaigns in affected regions.
  • Vaccination: Vaccination programs for poultry to reduce outbreak risk.
  • Recommendations: Emphasis on avoiding poultry contact and using protective equipment​ ​.

The ongoing global response to the H5N1 avian influenza outbreak involves coordinated efforts in surveillance, public health campaigns, research, and vaccination programs. These measures aim to prevent further human infections and control the spread among animal populations. Public health recommendations consistently emphasize avoiding contact with infected animals, using appropriate personal protective equipment, and ensuring safe food handling practices. The situation remains dynamic, requiring continuous monitoring and adaptation of strategies to mitigate the risk of widespread transmission.


The recent identification of a human case of avian influenza in Colorado highlights the ongoing threat posed by zoonotic diseases and the importance of vigilant monitoring and response efforts. Through the collaborative efforts of CDPHE, CDA, CDC, and other partners, Colorado is taking proactive measures to manage and mitigate the risks associated with avian influenza.

Public health experts continue to emphasize the importance of proper handling and cooking of poultry products, as well as the need for individuals who work with potentially infected animals to take appropriate precautions. Ongoing research and technological advancements, coupled with strong international collaboration, will be essential in the continued fight against avian influenza.

As the situation evolves, it is crucial for the public to stay informed and adhere to the guidance provided by health authorities. By working together, we can protect public health and ensure the safety of our food supply, while also addressing the broader challenges posed by avian influenza on a global scale.

APPENDIX 1- Technical Data on Human Infection with Avian Influenza A(H5) Viruses

Human infections with avian influenza A(H5) viruses, specifically the highly pathogenic avian influenza (HPAI) A(H5N1), continue to be a significant public health concern. These infections are primarily acquired through direct contact with infected animals or contaminated environments. Symptoms can range from mild respiratory illness to severe and fatal conditions.


From January 2003 to May 2024, a total of 889 cases of human infection with avian influenza A(H5N1) have been reported globally, with 463 fatalities (CFR of 52%). In the Western Pacific Region, 254 cases were reported from four countries (Cambodia, China, Lao PDR, and Vietnam), with 141 fatalities (CFR of 56%)​ (CDC)​​ (World Health Organization (WHO))​.

Recent Cases

  • A(H5N1) Virus: Between June 7 and June 13, 2024, no new human cases were reported in the Western Pacific Region. The last reported case in this region was in China on March 26, 2024​ (World Health Organization (WHO))​.
  • A(H5N6) Virus: One new case was reported from Fujian Province, China. The patient, a 41-year-old male, developed severe pneumonia and subsequently died. To date, 92 cases with 37 deaths (CFR 40%) have been reported in the Western Pacific Region since 2014​ (World Health Organization (WHO))​.

Technical Details

  • Virus Detection and Diagnosis:
    • Laboratory diagnosis of avian influenza in humans involves RT-PCR for viral RNA detection.
    • WHO provides periodic updates and protocols for molecular detection methods​ (World Health Organization (WHO))​.
  • Clinical Presentation:
    • Symptoms vary from mild upper respiratory infections to severe pneumonia, gastrointestinal symptoms, and encephalitis.
    • Cases have also been detected in asymptomatic individuals exposed to infected birds​ (World Health Organization (WHO))​.
  • Transmission:
    • Human-to-human transmission of HPAI A(H5) viruses is rare and has not been sustained.
    • Most human infections result from direct contact with infected birds or contaminated environments​ (World Health Organization (WHO))​​ (CDC)​.
  • Treatment and Prevention:
    • Antiviral drugs such as neuraminidase inhibitors (oseltamivir, zanamivir) can reduce viral replication and improve survival chances.
    • Public health measures include surveillance, monitoring exposed individuals, and recommendations to avoid contact with potentially infected animals and consuming raw or undercooked animal products​ (World Health Organization (WHO))​.

Detailed Scheme Table

Virus SubtypeCases Reported (Global)Fatalities (Global)Cases in Western PacificFatalities in Western PacificRecent CasesSymptomsTransmissionTreatmentPrevention
A(H5N1)889463254141None (June 2024)Respiratory, GI, EncephalitisRare human-to-humanOseltamivir, ZanamivirAvoid contact with infected birds, surveillance
A(H5N6)923792371 (June 2024)Severe pneumoniaRare human-to-humanAntiviral treatmentAvoid contact with infected birds, enhanced surveillance
A(H3N8)3131None (June 2024)Respiratory symptomsRare human-to-humanSupportive careAvoid contact with infected birds
A(H7N4)1010None (June 2024)Respiratory symptomsRare human-to-humanSupportive careSurveillance, biosecurity measures
A(H7N9)15686161568616None (June 2024)Respiratory symptoms, Severe pneumoniaLimited human-to-humanAntiviral treatmentAvoid contact with infected birds
A(H9N2)101210122 (June 2024)Mild respiratory symptomsRare human-to-humanSupportive careAvoid contact with infected birds
A(H10N3)3030None (June 2024)Respiratory symptomsRare human-to-humanSupportive careSurveillance, biosecurity measures
A(H10N5)1010None (June 2024)Respiratory symptomsRare human-to-humanSupportive careSurveillance, biosecurity measures

Public Health Recommendations

  • Surveillance: Ongoing monitoring and reporting of human cases and animal outbreaks.
  • Personal Protective Measures: Avoiding contact with sick or dead birds and ensuring proper cooking of poultry products.
  • Health Systems Preparedness: Ensuring healthcare facilities are equipped for early detection and treatment of avian influenza cases​ (CDC)​​ (World Health Organization (WHO))​​ (World Health Organization (WHO))​.

For more detailed information and continuous updates, please refer to the WHO and CDC websites.

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