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CDC Launches Influenza A Wastewater Surveillance Dashboard

NEW YORK – The US Centers for Disease Control and Prevention has launched a new interactive mapping tool reporting the results of influenza A wastewater surveillance using molecular testing.

The new map was added to the agency's existing webpage describing how it is monitoring influenza data to better understand the current avian influenza A H5N1 situation in people. It was also incorporated separately into the National Wastewater Surveillance System website.

The CDC previously reported that it has been piloting wastewater surveillance for flu A and planned to utilize that data to inform the agency's H5N1 strategies.

The current data shows that during the two most recent weeks of April 21 to May 4, a total of 230 of 674 wastewater sites in 34 states reported data that met the criteria for influenza A detection in both weeks or either week, and three sites, or 1 percent of sites, from three states were at a high level, designated as in the 80th percentile compared to levels recorded at that site between Oct. 1, 2023, and March 2, 2024.

Combined with seasonal surveillance systems, the flu A monitoring in wastewater can provide a more comprehensive picture of influenza activity, Jonathan Yoder, the deputy director for the Division of Infectious Disease Readiness & Innovation (DIDRI) at the CDC, said in an email.

Wastewater samples can be used to detect but not distinguish influenza A H5N1 from other flu A subtypes, but wastewater surveillance "enables us to monitor this issue on a national scale and detect increases in A(H5N1) to inform public health action," Yoder said, adding, "When we see unexpected fluctuations in levels of influenza A viruses within our wastewater system, we can proactively investigate other data systems for similar patterns." 

However, detection of flu A viruses in wastewater does not necessarily indicate undetected human cases, Yoder cautioned. 

"Influenza in wastewater can also come from other animal sources, such as birds or livestock, or their byproducts, such as raw cow milk products," Yoder said.

While it is possible that the wastewater surveillance data could be misinterpreted, "we believe that the value in being transparent with sharing the data that we have outweighed that risk," Yoder said.

The data can also potentially lead to better understanding of flu A transmission patterns, early detection of outbreaks, and improved response strategies.

"We are still learning about the relationships between influenza A levels in wastewater and H5N1 levels found in livestock or animal products — and wastewater data offers additional data to understand this evolving public health concern," Yoder also said.

The 80th percentile was chosen as a way to help public health officials prioritize where they may want to focus efforts for further investigation to better understand what may be happening in a particular community, including review of other human influenza A surveillance system data.

Importantly, Yoder said that this does not mean that the 80th percentile definitely indicates areas of concern, or that this is the only level at which public health actions should occur.

"Wastewater surveillance is an evolving science. Efforts to monitor influenza A virus activity using wastewater data are likely to evolve as the methodologies and interpretation are evaluated and refined," Yoder said.

For wastewater sites at a high level of influenza A virus levels, the CDC said it will work with public health and other partners to better understand sources that are contributing to that wastewater system.

The different jurisdictions are using a variety of PCR testing methods to identify influenza A in wastewater, Yoder said, which include a digital PCR assay developed by GT Molecular under contract with the CDC as part of a planned testing expansion.

The CDC encouraged state and local public health partners to begin testing for influenza A virus in the fall of 2023 and is continuing to enroll additional sites for influenza A monitoring as appropriate.

Currently, NWSS is overseeing flu A wastewater monitoring across 40 states.