The U.S. Centers for Disease Control and Prevention has launched a public dashboard featuring data on influenza A detected in wastewater. This tool could help track the outbreak of H5N1 bird flu, which has recently infected cattle herds.
Between April 21 and May 4, a total of 230 out of 674 sites in 34 states reported “data suitable for analysis for influenza A virus” — admittedly, however, the agency didn’t define what this designation meant. It went on to say, of these, three sites (1 percent) from three states reported high levels of the virus, exceeding the 80th percentile compared to data from October 1, 2023, to March 2, 2024.
The CDC was clear to state that its wastewater testing cannot determine the source of the influenza A virus: It could come from a human or from an animal (like a bird) or an animal product (like milk from an infected cow).
Although the threat to humans from the virus is currently classified as low, scientists are vigilant for any changes that could facilitate its spread among people. Wastewater testing, a method proven effective during the COVID-19 pandemic, is being used to detect mutations in influenza viruses.
For the week ending May 4, the CDC’s surveillance system did not indicate any unusual influenza activity in humans, including the H5N1 virus. Since late March, the virus has been detected in dairy cattle across nine U.S. states. Notably, unusually high levels of influenza A were found in Saline County, Kansas. The U.S. Department of Agriculture confirmed positive tests in four cattle herds in Kansas, with the latest on April 17. However, specific counties were not disclosed.
The CDC is monitoring various flu indicators to track influenza A, including H5N1, and is particularly attentive to potential human infections in areas where the virus has been identified. The agency compares recent influenza A levels in wastewater to those recorded from October 2023 to March 2024 at the same sites. Levels at or above the 80th percentile are considered high.
Despite the benefits of this testing, it cannot pinpoint whether the virus came from birds, humans, or milk.
“By tracking the percentage of specimens tested that are positive for influenza A viruses, we can monitor for unusual increases in influenza activity that may be an early sign of the spread of novel influenza A viruses, including H5N1,” the CDC stated in its report.
The public database allows individuals to check for increases in influenza A cases in their area or spot any unusual flu activity.
It’s important to note that current wastewater monitoring methods detect influenza A viruses but do not determine the subtype. This means that avian influenza A (H5N1) viruses can be detected but would not be distinguished from other influenza A virus subtypes.
Public health officials at CDC and state and local health departments monitor these data. For areas where influenza A virus levels in wastewater are high, CDC works with relevant partners to better understand the factors that could be contributing to these levels.