The U.S. Centers for Disease Control and Prevention (CDC) on Tuesday released data on influenza A found in wastewater in a public dashboard that could assist in tracking the outbreak of H5N1 bird flu that has infected cattle herds.

Last week, an agency official told Reuters about U.S plans to make public data collected by its surveillance system.

While the threat from the virus to people has been classified as low at this time, scientists are closely watching for changes in the virus that could make it spread more easily among humans.

Testing wastewater from sewers proved to be a powerful tool for detecting mutations in the SARS-CoV-2 virus during the COVID-19 pandemic.

For the week ended May 4, the agency's surveillance system did not show any indicators of unusual influenza activity in people, including the H5N1 virus. The virus has been detected among dairy cattle in nine U.S. states since late March.

The testing did detect unusually high levels of influenza A in Saline County, Kansas. The U.S. Department of Agriculture has confirmed four herds tested positive in Kansas, the last on April 17. Neither Kansas nor USDA have posted the counties where the herds were located.

CDC said that it is actively looking at multiple flu indicators to monitor for influenza A, of which H5N1 is a subtype, including looking for signs of spread of the virus to, or among, people, in areas where it has been identified.

For monitoring influenza A virus in wastewater, CDC compares the most recent weeks of influenza A virus levels recorded at a wastewater site to levels reported between Oct. 1, 2023 and March 2, 2024 for that same wastewater site. Those at or above the 80th percentile are categorized as high.

However, the testing cannot identify the source of the virus or whether it came from an infected bird, human 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 spread of novel influenza A viruses, including H5N1," the CDC said in its report.

The public database will allow individuals to check for increases in influenza A cases in their area, or spot any unusual flu activity. (Reporting by Bhanvi Satija in Bengaluru; Additional reporting by Julie Steenhuysen and Tom Polansek in Chicago; Editing by Bill Berkrot)