H5N1 Bird Flu: First US Case in Child – California 2024

The Centers for Disease Control and Prevention (CDC) has confirmed the first case of avian influenza A(H5N1) – commonly known as bird flu – in a child in the United States. The case, identified in California, is prompting increased surveillance but currently doesn’t signal a change in public health risk assessment, which remains low. The child experienced mild symptoms and has since recovered after receiving antiviral medications.

Tracking the Virus: Current Situation and Human Cases

This case is particularly noteworthy as it’s the first confirmed H5N1 infection in a child within the U.S. Since February 2024, a total of 71 human cases of H5 bird flu have been reported across the country, with 29 of those occurring in California. However, the CDC has streamlined its reporting of these cases, now integrating them into routine influenza data updates as of July 7, 2025. Detailed data on monitoring and testing are available monthly through the CDC’s A(H5) Bird Flu Surveillance and Human Monitoring page. It’s important to note that the USDA data on animal infections are now reported directly by the USDA, and are no longer included on the CDC website.

The California Department of Public Health (CDPH) is currently investigating the source of the child’s infection. Initial investigations revealed that other household members experienced symptoms, but testing did not detect the H5N1 virus in them. Some family members did test positive for other common respiratory viruses. Contact tracing is ongoing, but, crucially, there is currently no evidence of person-to-person transmission linked to this case. This aligns with the pattern observed in all other H5N1 cases reported in the United States to date.

What is H5N1 and Why the Concern?

Avian influenza A(H5N1) is a virus that naturally circulates among wild birds. It can sometimes spread to domestic poultry and, less frequently, to mammals, including humans. The current outbreak has been widespread globally, affecting wild birds and causing outbreaks in poultry farms. More recently, the virus has been detected in U.S. Dairy cows, beginning in August 2024 in California, raising concerns about potential spillover to humans. The virus is classified as “highly pathogenic,” meaning it can cause severe disease in birds.

Human infections with H5N1 are rare, but can range in severity. Most cases have involved direct contact with infected birds. The CDC notes that limited and sporadic human infections where animal exposure isn’t identified are uncommon, but have been reported in other countries. This underscores the importance of continued surveillance.

Detection and Surveillance Efforts

This particular case was identified through routine influenza testing, highlighting the importance of existing surveillance systems. The CDC is closely monitoring data from these systems, particularly in states experiencing outbreaks in animals. Enhanced surveillance, including influenza A virus subtyping of specimens, even from individuals without known exposure, played a role in identifying a similar case in California in December 2024, as detailed in a report published by the CDC’s Morbidity and Mortality Weekly Report (MMWR). That case too involved a school-aged child with no identified source of exposure, and no evidence of human-to-human transmission.

Understanding the Testing Process

When a sample tests positive for H5 at a public health laboratory, further confirmation is required at the CDC. If CDC testing cannot confirm the H5 infection, the case is classified as “probable,” following guidance from the Council of State and Territorial Epidemiologists (CSTE). This nuanced classification reflects the complexities of viral detection and the need for rigorous confirmation.

Risk Assessment and Recommendations

The CDC maintains that the overall risk to the general public remains low. However, individuals with exposure to infected or potentially infected animals – including birds, poultry, dairy cattle, and other livestock – are at a higher risk of infection. The CDC strongly recommends avoiding unprotected contact with sick or dead animals. This includes wild birds, poultry, and other domesticated or wild animals.

It’s important to distinguish between relative and absolute risk. While any human case of H5N1 is concerning, the number of cases remains relatively small compared to the millions of people who contract seasonal influenza each year. The CDC’s risk assessment is based on a careful evaluation of the available data, including the limited evidence of human-to-human transmission.

What to Expect Moving Forward

The CDC will continue to provide updates as more information becomes available. Public health officials are focused on several key areas: continued surveillance of both animal and human populations, rapid detection and investigation of new cases, and ongoing monitoring for any signs of changes in the virus that could increase its transmissibility to humans. The agency is also working with state and local health departments to ensure that they have the resources and expertise needed to respond to potential outbreaks. Further research is needed to better understand the virus and its potential to cause human illness. For more information, you can refer to the California Department of Public Health’s statement regarding this case: State Reports Single, Possible Case of Bird Flu Virus in Child with Mild Symptoms.