CDC wastewater team lead Amy Kirby told Reuters on Thursday that the agency has identified spikes of influenza A, of which H5N1 is a subtype, in a handful of sites and is investigating the source. She said there is no indication of human infection with H5N1.

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

Kirby said the CDC has been collecting influenza data in wastewater in about 600 sites since at least last fall to better track respiratory infections. That data can now be helpful in tracking the outbreak of H5N1 bird flu that has infected 42 dairy herds in nine U.S. states, and one dairy farm worker.

Scientists are closely watching for changes in the virus that could make it spread more easily among humans.

The wastewater tests are capable of detecting many types of influenza A, including the H5N1 subtype, but the findings do not indicate the source of the virus or whether it came from a bird, cow, milk or from farm runoff or humans.

The dashboard will allow individuals to check for increases in influenza A in their area, and compare it with historical data where available. Seasonal influenza cases have fallen off sharply, so spikes could offer a signal about unusual flu activity.

So far, testing has identified some increases in the presence of flu in samples that are "very localized in only a handful of sites," Kirby said.

What is surprising, she said, is the outbreak in cattle and the presence of virus in milk, which sometimes makes its way into wastewater. The agency is now working to identify what factors are contributing to the wastewater findings, including understanding the presence of milk in wastewater.

'NOT WORRIED ABOUT THE COWS'

Dr. Marc Johnson, a virologist at the University of Missouri who developed a wastewater monitoring system for COVID, and other scientists have developed tests that can identify H5N1 in wastewater samples, but he said the CDC is discouraging use of such tests.

Kirby said such widespread testing would be a drain on resources and ultimately would not identify the source of the virus, although there may be times when such subtyping is needed.

"It really doesn't get us any further to knowing what the source of this is. Is it dairy? Or is it human? Or is it wild birds? Or is it poultry? All of those things are still on the table," she said. "It doesn't get us any farther down the road."

Johnson said such tests put scientists in a better position to track changes in the virus.

"I'm not worried about the cows. I'm not worried about the milk. But I'm worried that there are lots of other animals that it can jump to, and eventually it's going to find a combination that can make it into humans if we're not careful," he said.

Academic researchers working with Verily, a health sciences unit of Alphabet (GOOGL.O), already demonstrated how wastewater can help in the outbreak.

Their not yet peer-reviewed paper, posted on medRxiv, identified the virus in three wastewater plants in two Texas cities where infected cattle were present.

Using archived samples, they identified bird flu in wastewater as early as Feb. 25, before the first reports of cattle with unknown illnesses on March 7, and a full month before Texas confirmed H5N1 in dairy cattle.

"That represents a really significant lead time that we can have if we're implementing this work as widely and as readily as we should be as a country," said Dr. Marlene Wolfe, from Emory University in Atlanta and program director of WastewaterSCAN, a wastewater detection program supported by Verily.