in wastewater and sites with high levels* of influenza
A virus or H5 detections reported to CDC —
United States, May 12–July 13, 2024†
#18,304
Wastewater surveillance has long been hailed as an important adjunct to traditional surveillance methods, often providing early warning of undetected diseases in a community. In 2022, it was instrumental in detecting the presence of Polio in New York state (see New York State DOH Statement On Polio Investigation - Detection In Wastewater).
With testing for COVID during the pandemic switching primarily to home testing, wastewater analysis has allowed health officials to track the waves of the virus across the nation, and has provided samples of variants for study (see BMC Genomics: Chronic Shedding of a SARS-CoV-2 Alpha Variant in Wastewater).
Since HPAI H5N1 appeared in cattle in March of this year, and subsequently spilled over into cattle and poultry workers over the summer, wastewater surveillance has been used to look for unusual clusters of influenza A - and from a smaller subset of reporting stations - evidence of H5 influenza.
A few past blogs include:
Today the CDC has published an MMWR report on the importance of wastewater surveillance and its current limitations. Due to its length, I've only posted the link, summary, and some excerpts. Follow the link to read the report in its entirety.
I'll have a brief postscript after you return.
Wastewater Surveillance for Influenza A Virus and H5 Subtype Concurrent with the Highly Pathogenic Avian Influenza A(H5N1) Virus Outbreak in Cattle and Poultry and Associated Human Cases — United States, May 12–July 13, 2024
Weekly / September 19, 2024 / 73(37);804–809
Souci Louis, VMD1,2; Miguella Mark-Carew, PhD2; Matthew Biggerstaff, ScD3; Jonathan Yoder, MPH2; Alexandria B. Boehm, PhD4; Marlene K. Wolfe, PhD5; Matthew Flood, PhD6; Susan Peters, DVM6; Mary Grace Stobierski, DVM6; Joseph Coyle, MPH6; Matthew T. Leslie, DVM, PhD7; Mallory Sinner, MPH7; Dawn Nims, MPH7; Victoria Salinas, MPH8; Layla Lustri, MPH8; Heidi Bojes, PhD8; Varun Shetty, MD8; Elisabeth Burnor, MSc9; Angela Rabe, MAS9; Guinevere Ellison-Giles, MPH9; Alexander T. Yu, MD9; Austin Bell, MPH10; Stephanie Meyer, MPH10; Ruth Lynfield, MD10; Melissa Sutton, MD11; Ryan Scholz, DVM12; Rebecca Falender, DVM13; Shannon Matzinger, PhD14; Allison Wheeler, MSPH14; Farah S. Ahmed, PhD15; John Anderson, PhD15; Kate Harris, MS16; Austin Walkins, MS16; Surabhi Bohra, MHS17; Victoria O’Dell, MPH17; Virginia T. Guidry, PhD18; Ariel Christensen, MPH18; Zack Moore, MD18; Erica Wilson, MD18; Joshua L. Clayton, PhD19; Hannah Parsons, MPH19; Krista Kniss, MPH3; Alicia Budd, MPH3; Jeffrey W. Mercante, PhD2; Heather E. Reese, PhD2; Michael Welton, PhD20; Megan Bias, MPH2; Jenna Webb, MPH21; Daniel Cornforth, PhD2; Scott Santibañez, MD, DMin2; Rieza H. Soelaeman, PhD2; Manpreet Kaur, MPH2; Amy E. Kirby, PhD2; John R. Barnes, PhD2; Nicole Fehrenbach, MPP2; Sonja J. Olsen, PhD3; Margaret A. Honein, PhD2 (VIEW AUTHOR AFFILIATIONS)View suggested citation
Summary
What is already known about this topic?
Wastewater surveillance can detect influenza A virus and the H5 subtype, although current testing does not distinguish between human and animal sources.
What is added by this report?
During May 12–July 13, 2024, high influenza A virus levels were detected in wastewater in four states, including three states with seasonal human influenza virus activity noted during this time. The H5 subtype was detected in wastewater in nine states; follow-up investigations in many of these states revealed likely animal-related sources, including those related to milk processing.
What are the implications for public health practice?
Early work to interpret influenza A virus and H5 subtype detections in wastewater can help with public health preparedness and response for the upcoming respiratory illness season.
Article PDF
Full Issue PDF
Abstract
As part of the response to the highly pathogenic avian influenza A(H5N1) virus outbreak in U.S. cattle and poultry and the associated human cases, CDC and partners are monitoring influenza A virus levels and detection of the H5 subtype in wastewater. Among 48 states and the District of Columbia that performed influenza A testing of wastewater during May 12–July 13, 2024, a weekly average of 309 sites in 38 states had sufficient data for analysis, and 11 sites in four states reported high levels of influenza A virus. H5 subtype testing was conducted at 203 sites in 41 states, with H5 detections at 24 sites in nine states.
For each detection or high level, CDC and state and local health departments evaluated data from other influenza surveillance systems and partnered with wastewater utilities and agriculture departments to investigate potential sources. Among the four states with high influenza A virus levels detected in wastewater, three states had corresponding evidence of human influenza activity from other influenza surveillance systems.
Among the 24 sites with H5 detections, 15 identified animal sources within the sewershed or adjacent county, including eight milk-processing inputs. Data from these early investigations can help health officials optimize the use of wastewater surveillance during the upcoming respiratory illness season.
(SNIP)
Limitations
The findings in this report are subject to at least five limitations.
- First, although influenza viruses can be detected in wastewater, current techniques cannot distinguish between human and animal sources, and the current approach for H5 testing in wastewater is not specific to HPAI A(H5N1) viruses; H5 detections in wastewater might reflect animal rather than human infections and might be detection of low pathogenic avian influenza rather than HPAI A(H5N1) viruses.
- Second, limited data are available regarding the proportion of persons infected with influenza viruses who shed virus in urine or feces, and how the concentration of viral shedding varies by subtype and across the course of illness (10).
- Third, population wastewater surveillance coverage varies substantially by state; therefore, data are most informative when used in conjunction with clinical human influenza surveillance data.
- Fourth, states reported information on the investigations of sewershed inputs for sites with high influenza A virus levels or H5 detections, but comparison information for sites without these signals was not collected; therefore, epidemiologic measures for these possible associations could not be generated.
- Finally, the comprehensiveness of data collection after a signal in wastewater varied widely. Public health investigations into potential sources of H5 viruses in wastewater can be complex (e.g., milk-processing inputs can include milk from other states) and might support or refute likely sources of H5 without providing definitive conclusions.
Implications for Public Health Practice
Lessons learned during early follow-up investigations of wastewater signals can help health officials implement an improved measure of influenza A virus levels in wastewater and optimize the use of wastewater surveillance during the upcoming respiratory illness season.
The findings in this report, and data from wastewater surveillance in general, can complement traditional influenza surveillance systems. A One Health approach with multisectoral collaboration and data-informed guidance on when and how to use influenza virus subtyping of wastewater might enhance the public health response to the current outbreak.
While wastewater surveillance is undoubtedly an excellent tool, in far too many cases this summer we've seen it used as a substitute for - not an adjunct to - traditional influenza surveillance. Even when H5 signals have been detected - or human infections have been confirmed - many states have refused help from the CDC's epidemiological detectives.
Despite the remarkable work by the teams uncovering H5 detections at 24 sites in nine states, we still don't know with any certainty whether the source was human, animal, or both.
The current strategy of `don't test, don't tell' - adopted by many states - may avoid near-term pain, embarrassment, or economic losses, but it leaves us wide open to being blindsided by a much bigger crisis down the road.
