- The Centers for Disease Control and Prevention has begun publishing wastewater data to help track the bird flu in the U.S.
- The disease is primarily spreading among birds, but has been detected in cattle as well.
- Wastewater testing is a vital early warning system designed to spot emerging viral outbreaks.
- The current threat to people is considered low.
Bird flu, also known as the H5N1 virus, has infected cattle in nine states, according to data from the Centers for Disease Control and Prevention (CDC).
To track the spread of the disease, the CDC has begun reporting wastewater data.
Although it has affected millions of birds and other animals in the last 2 years, its risk to humans is still considered low. Just one person in the U.S. has developed H5N1 in recent months.
Bird flu can have a 50% fatality rate, but has not spread widely to humans
Since January 2022 in the U.S., the H5N1 virus has killed over 90 million birds across 48 states.
It also sporadically jumped into mammal species in the U.S., including mountain lions, bears, bobcats, coyotes, raccoons, minks, and skunks.
More recently, the virus has moved into a new host: cattle. Although cattle are less seriously affected than other species, this can make it harder to track where the disease is spreading.
Because the virus rarely kills cows, infected animals can continue to live among their herd, providing more opportunities for the virus to pass to other cattle and species.
In April 2024, the United States recorded its first cow-to-human transmission of H5N1 in a dairy farm worker in Texas. This is only the second human case of H5N1 to be identified in the U.S. ever; the first was in 2022.
So far, there has been no recorded human-to-human transmission of the virus.
Krzysztof Pyrć, PhD, a professor of biological sciences and leader of the Virology Laboratory at the Malopolska Centre of Biotechnology at the Jagiellonian University in Poland said that the first human cases of H5N1 were discovered in the 1990s.
“Since then,” he explained, “roughly 1,000 cases have been recorded in humans, approximately 50% of which were fatal.”
“Since 2020, we have a new subtype that is much more transmissible, causing a pandemic in birds with multiple outbreaks recorded worldwide,” he said.
This includes infections in mammals, including marine mammals in South America, farmed foxes in Finland, and cats in Poland.
Where are H5N1 levels highest?
The CDC considers the threat posed to people by H5N1 to be “low,” but they are closely monitoring the outbreak. They have launched a new dashboard monitoring wastewater.
Their National Wastewater Surveillance System (NWSS) takes data from more than 600 sites across the U.S. and compares current levels of the virus with those from 2023.
According to the CDC, most wastewater monitoring cannot tell the difference between H5N1 and other types of influenza A viruses. However, detecting large differences between this year’s levels and the levels from 2023 is a signal that H5N1 is involved.
Compared with last year’s data, during the week ending the 4th of May, levels of influenza A viruses were “above average” in 10 sampling regions out of 230:
- Pinellas County FL,
- Randall/Potter County TX,
- Montgomery County TX,
- Sonoma County CA,
- Webb County TX,
- Marin County CA,
- Oswego County NY,
- San Francisco/San Mateo County CA,
- Placer County CA,
- Santa Clara County CA.
Levels of the virus were deemed “high” in one region:
- Saline County, KS
Regions where cattle have been infected
To date, nine states have identified H5N1 outbreaks in cattle:
- Michigan: 14 herds
- Texas: 13 herds
- New Mexico: eight herds
- Idaho: five herds
- Kansas: four herds
- Colorado: two herds
- Ohio: one herd
- North Carolina: one herd
- South Dakota: one herd
The importance of wastewater monitoring
A recent paper from the Texas Epidemic Public Health Institute identified nine cities in Texas where H5N1 was detected in the wastewater between March 4th and April 25th. The paper is a pre-print and has yet to be published in a peer-reviewed journal.
The research used data from the Texas Wastewater Environmental Biomonitoring Network (TexWEB network) which focuses on the early detection of pathogens.
“For approximately 2 years, TexWEB has been monitoring the wastewater of multiple municipalities across Texas,” the study authors said in an emailed statement.
Using genetic information, the researchers can “monitor the levels and sequence of hundreds or even thousands of viruses in a single sample.”
The study authors told Healthline that, until March 2024, they had not identified any H5N1 viruses. However, “After early March,” they explained, “we have seen H5N1 in multiple sites and we continue to see H5N1 up until the most recent sampling.”
How can wastewater monitoring help?
The Texas-based researchers told Healthline that data from wastewater acts “as an early sentinel signal of where known or emerging viruses are present within the catchment area of a wastewater treatment plant.”
They then pass this information to local and state public health departments, which can begin planning and increasing their surveillance efforts.
Although wastewater monitoring is a vital part of detecting emerging viral outbreaks, it does have certain limitations.
For instance, the researchers explain that TexWEB cannot identify where the virus is coming from, so it could be from “wild birds, agriculture, food processing, or mammals, including humans.”
Should people be worried about a bird flu outbreak?
“At this point, there is no evidence for human-to-human transmission, and pasteurized milk has been shown to be safe,” the researchers from Texas told Healthline.
However, they also said that “TexWEB continues to monitor for emerging mutations that may increase virulence or transmissibility to mammalian hosts.”
We asked Pyrć whether the H5N1 virus could spark a new pandemic. “Unfortunately, the answer is yes.”
“Luckily,” he continued, “for now, the virus does not thrive in the human body, and only a few cases have been reported globally. Can this change? Yes, it can, but we cannot predict when it will happen and how severe the disease caused by a new variant will be in humans.”
We also asked what global health organizations should do to slow transmission. He answered our question with a question:
“Are individual countries and politicians prepared to brace for the next threat and follow the advice given by international agencies? Are they ready to allow professional agencies to operate without political pressure?”
While bird flu certainly is a serious threat, Pyrć believes we should “prepare for it, but we should not panic.”
The takeaway
The H5N1 virus has infected millions of birds and other mammals. Recently, it has “jumped” into cattle in nine states. So far, there has only been one case of cattle-to-human transmission and no human-to-human transmission.
The CDC is closely monitoring the situation, and wastewater analysis is just one of their tools. Although we do not know the virus’ next move, for now, we do not need to worry.
