Scientists watching wastewater for signs of H5N1 as U.S. bird flu outbreak in dairy cattle grows

Scientists in the U.S. and Canada are watching wastewater for early signs of H5N1 as an outbreak of bird flu among American dairy cattle keeps growing.

With cases confirmed in dozens of herds across nine states - and roughly 300 peo‐ ple being tested or moni‐ tored for symptoms after the detection of one human case - the U.S. Centers for Disease Control and Prevention (CDC) is aiming to launch an online dashboard for wastewater monitoring as soon as Friday.

At a handful of sites, the agency has already spotted spikes of influenza A, of which H5N1 is a subtype, and is investigating the source, the CDC's wastewater team lead Amy Kirby told Reuters.

More than 600 facilities across the U.S. report data on influenza A. While waste‐ water testing doesn't distin‐ guish between various types, it can offer signals of "un‐ usual levels" of the virus, the CDC said this week.

Similar efforts have been used to track other emerging infections, including the viruses behind COVID-19 and mpox, providing early clues that case counts may be ris‐ ing in communities before other metrics such as hospi‐ talizations creep up.

Other American re‐ searchers, not affiliated with the CDC, have already shown wastewater's ability to signal the spread of H5N1.

Their early study, which hasn't yet been peer-re‐ viewed, used archived waste‐ water samples to detect signs of bird flu from three sites in Texas as far back as February - weeks before the first confirmed infections in the state's dairy cattle.

Unusual data triggers investigations to find source

Typically, wastewater sam‐ ples are gathered from sites that collect large amounts of raw sewage. That means re‐ searchers can't automatically determine the specific source of a positive sample - like whether it flowed in from residential toilets, or a farm or if the infected host was a human or animal.

When tracking H5N1 across the U.S., the CDC's newly developed metrics will include current influenza A levels for specific sewer sys‐ tems, compared to levels de‐

tected during last year's flu season.

WATCH | Human bird flu case linked to U.S. dairy cattle outbreaks:

Any unusual activity in the U.S. data would be simple to spot since North America's regular flu season has died down. Increased levels would trigger CDC investigations to figure out the exact source, such as waste coming from a milk processing plant.

Epidemiologist Megan Di‐ amond, who spearheads the Rockefeller Foundation's global wastewater surveil‐ lance portfolio, said adding wastewater to H5N1 surveil‐ lance efforts alongside other forms of testing is the right move.

"When we're constantly monitoring for pathogens in this kind of continuous ap‐ proach, we are able to shift from being reactive to proac‐ tive," she told CBC News.

Ontario scientists moni‐ tor for local flu spikes

In Canada, though waste‐ water monitoring is still being used to track COVID19, it's not part of expanded federal H5N1 surveillance ef‐ forts, which now include milk testing and restrictions on imported cattle. (There are no reports yet of the virus in‐ fecting Canadian dairy cows, though it has been reported in more than 10 million wild and farmed birds.)

Some Canadian re‐ searchers are taking matters into their own hands.

Lawrence Goodridge, di‐ rector of the Canadian Re‐ search Institute for Food Safety and a professor at the University of Guelph, said his team started tracking in‐ fluenza in Ontario waste‐ water a few months ago to study trends in human infec‐ tions, and are now pivoting to see if any H5N1 shows up.

Unlike the U.S., their ap‐ proach is directly monitoring for the H5N1 subtype using a genomic sequencing assay, rather than watching for in‐ creases in broader forms of influenza. The team gets samples from five areas in Southwestern Ontario, sever‐ al of which are in regions with high levels of milk pro‐ duction.

"We're seeing very low lev‐ els, if any, of influenza right now," Goodridge said. "So if we should see a sudden spike, particularly in influen‐ za A, that would certainly get our attention."

The team hasn't spotted any unusual signals just yet, he told CBC News on Friday.

Cattle, worker testing also needed, but chal‐ lenging

Diamond stressed that wastewater samples flow in from so many sewage sys‐ tems that the situation can change on a dime. "You're not seeing anything, you're not seeing anything - and then all of a sudden, you get a light up."

Broader testing of cattle and farm workers in the U.S. is another piece of the puz‐ zle, but that process can be fraught with challenges, Dia‐ mond added. Human testing requires getting consent and can be costly. And if officials want to enter dairy farms, rules and regulations slow the process down.

The U.S. federal govern‐ ment did announce major funding to expand those ef‐ forts on Friday, with tens of millions for states and livestock farms to beef up protective measures and testing for the virus, ac‐ cording to U.S. media re‐ ports. That includes the CDC paying up to $75 to farm workers who take part in studies, noted the Washing‐ ton Post.

Still, Diamond noted tar‐ geted testing may only reveal the "tip of the iceberg" com‐ pared to widespread waste‐ water monitoring. "By imple‐ menting a multifaceted strategy of different tools, that's where you kind of get that comprehensive view of what's happening."

WATCH | How waste‐ water surveillance helps scientists track outbreaks:

And it could offer an early warning system on both sides of the border.

"When you look around the U.S. and Canada, because we're talking in that bounded geography here, there are so many sites that are doing consistent monitoring for dif‐ ferent pathogens," Diamond said.

"And so adding in ... H5N1 would truly empower [health officials] to understand if in‐ fluenza A is in their commu‐ nity."