Commonground
Senior Moderator
Weekly / February 27, 2025 / 74(6);102–106
Rebecca Falender, DVM[SUP]1[/SUP]; Tyler S. Radniecki, PhD[SUP]1[/SUP]; Christine Kelly, PhD[SUP]1[/SUP]; Paul Cieslak, MD[SUP]2[/SUP]; David Mickle[SUP]1[/SUP]; Harrison Hall[SUP]3[/SUP]; Ryan Scholz, DVM[SUP]3[/SUP]; Melissa Sutton, MD[SUP]2[/SUP](VIEW AUTHOR AFFILIATIONS)
Summary
What is already known about this topic?
Highly pathogenic avian influenza A(H5N1) outbreaks have emerged in U.S. cattle and poultry. Wastewater surveillance detects influenza A(H5) subtype but does not currently distinguish between human and animal sources.
What is added by this report?
During September 15, 2021–July 11, 2024, retrospective analysis of wastewater surveillance data revealed 21 avian influenza A(H5) subtype detections across 12 Oregon communities. No association was found between detections in a community’s wastewater and history of a poultry outbreak or presence of dairy processing facilities or dairy farms within the sewershed. Avian influenza A(H5) was detected most frequently in two communities with important wild bird habitats.
What are the implications for public health practice?
Wastewater surveillance was an early indicator of avian influenza emergence in Oregon. Nonhuman and noncattle animal inputs, including wild birds, are an essential consideration when interpreting A(H5) subtype detections in wastewater.
Abstract
Wastewater surveillance is an important tool in the surveillance of emerging pathogens and has been leveraged during the highly pathogenic avian influenza (HPAI) A(H5N1) virus outbreak in cattle and poultry in the United States. Interpretation of avian influenza A(H5) subtype detections in wastewater requires an understanding of human and animal contributors to the sewershed because current testing does not distinguish between human and animal sources. Potential animal contributors include wild birds, farms with poultry or dairy cattle outbreaks, and dairy processing facilities. Retrospective analysis of 551 influenza A virus–positive wastewater surveillance samples from 20 sites in Oregon during September 15, 2021–July 11, 2024, revealed 21 avian influenza A(H5) subtype detections across 12 communities. Avian influenza A(H5) subtype detections in wastewater began approximately 6 weeks before Oregon’s first HPAI outbreak in domestic poultry, 7 weeks before Oregon’s first avian influenza A(H5) detection in wild birds, and 2 years before the first HPAI A(H5N1) outbreak in dairy cattle in the United States (Oregon has not detected HPAI A(H5N1) in dairy cattle or milk). No association was found between detection of avian influenza A(H5) in a community’s wastewater and history of an HPAI A(H5) outbreak among poultry in the county or presence of dairy processing facilities or dairy farms within the sewershed. Avian influenza A(H5) was detected most frequently in two communities with important wild bird habitats. Animal inputs, including from wild birds, should be considered when interpreting avian influenza A(H5) subtype detections in wastewater.
-snip-
Results
Regional Characterization
Among 551 influenza A virus−positive samples during September 15, 2021–July 11, 2024, 21 (3.8%) tested positive for the avian influenza A(H5) subtype (Figure 1) in 12 of 20 communities (Figure 2). The highest number of detections (five of 34) occurred in Ontario (Malheur County); the largest proportion of detections (three of 14) was in Newport (Lincoln County). Eight of 12 communities with avian influenza A(H5) subtype detections are within counties that previously had an outbreak of HPAI in poultry. Only four of 12 communities with avian influenza A(H5) subtype detections had a licensed Grade A dairy processing facility or dairy farm within the sewershed. The avian influenza A(H5) subtype was not detected in wastewater from the two sewersheds with the highest number of licensed Grade A dairy processing facilities (Portland [seven]) and Grade A dairy farms (Tillamook [13]). No association between avian influenza A(H5) subtype detections in wastewater and location within a county with a history of poultry outbreak (p = 0.65) or location of licensed grade A dairy processing facilities or dairy farms within the sewershed (p = 0.65) was identified.
Longitudinal Characterization
The avian influenza A(H5) subtype was detected during multiple weeks of each of the three influenza seasons during the study as well as during the summer of 2024 (Figure 1). The avian influenza A(H5) subtype was first detected in Oregon wastewater on March 21, 2022, approximately 7 weeks before avian influenza A(H5) was detected in wild birds (Figure 1) and approximately 6 weeks before HPAI was detected in poultry in Oregon (Figure 1).
Discussion
Wastewater surveillance in Oregon first detected the avian influenza A(H5) subtype on March 21, 2022, 6 weeks before HPAI A(H5) was identified in an Oregon domestic poultry outbreak, 7 weeks before avian influenza A(H5) was identified through Oregon wild bird surveillance, and 2 years before HPAI A(H5N1) was detected in dairy cattle in the United States (1). In this retrospective analysis, avian influenza A(H5) subtype detections in wastewater were not associated with poultry outbreaks or the presence of licensed dairy processing facilities or farms within the sewershed. Importantly, many avian influenza A(H5) detections occurred before the spillover of the virus into dairy cattle, estimated to have occurred during November 2023–January 2024,[SUP]¶[/SUP] and no HPAI A(H5N1) outbreaks in dairy cattle have been identified in Oregon (4). These results do not support poultry or licensed dairy farm or processing facilities as the etiology of the avian influenza A(H5) subtype in Oregon wastewater and suggest that noncattle animals, suspected to be wild birds, are a significant animal contributor to wastewater within the state.
Oregon is located along the Pacific Flyway, a major north-south route for migratory birds in the Americas that extends from Alaska to Patagonia. An estimated 1 billion birds traverse the Pacific Flyway yearly, and Oregon contains many important stopover sites (7). Animal input can enter wastewater via stormwater in combined (i.e., open) sewersheds or via leaking pipes within separate (i.e., closed) sewersheds, as well as through the dumping of animal products into the sewer system (6,8). Surveillance programs that sample from wastewater clarifiers might also capture excreta from wild birds that have been observed using clarifiers and lagoons as resting habitats. The two communities in Oregon with the most avian influenza A(H5) subtype detections contain important habitats for migratory wild birds, including seasonal wetlands (Ontario) and estuaries of major rivers (Newport) (7,9). Avian influenza A(H5) subtype detections occurred in both combined and separate sewersheds.
Limitations
The findings in this report are subject to at least two limitations. First, avian influenza A(H5) testing was performed retrospectively on samples that had tested positive for influenza A virus as part of Oregon’s routine influenza wastewater surveillance, which, before October 2023, occurred only during the influenza season. This approach limits the ability to describe seasonal avian influenza A(H5) subtype wastewater trends. Second, the testing methods used do not distinguish between animal sources or high- and low-pathogenic avian influenza A(H5) viruses (10).
Implications for Public Health Practice
The timing and spatial clustering of avian influenza A(H5) subtype detections in Oregon wastewater suggest that noncattle animals, suspected to be wild birds, are important contributors of the virus to Oregon’s wastewater. Oregon’s first avian influenza A(H5) subtype detections in wastewater did not occur until after the introduction of the 2.3.4.4b clade into wild birds in North America and preceded Oregon’s first HPAI poultry outbreaks and avian influenza A(H5) detections through wild bird surveillance by more than 6 weeks. The first avian influenza A(H5) subtype detection in Oregon wastewater occurred almost 2 years before the multistate outbreak of HPAI A(H5N1) in dairy cattle, excluding cattle as a potential source for subtype detections before November 2023. On the basis of the results of this retrospective study, continued intermittent detections of the avian influenza A(H5) subtype in wastewater are anticipated, even in the absence of outbreaks in dairy cattle or occurrence of human cases. Wild birds, in which HPAI A(H5) is now enzootic, are an important consideration when interpreting avian influenza A(H5) subtype detections in wastewater. Wastewater surveillance, with consideration of all animal contributors and in conjunction with other surveillance metrics, has the potential to strengthen ongoing avian influenza surveillance efforts.
https://www.cdc.gov/mmwr/volumes/74/wr/mm7406a5.htm?s_cid=mm7406a5_w
Rebecca Falender, DVM[SUP]1[/SUP]; Tyler S. Radniecki, PhD[SUP]1[/SUP]; Christine Kelly, PhD[SUP]1[/SUP]; Paul Cieslak, MD[SUP]2[/SUP]; David Mickle[SUP]1[/SUP]; Harrison Hall[SUP]3[/SUP]; Ryan Scholz, DVM[SUP]3[/SUP]; Melissa Sutton, MD[SUP]2[/SUP](VIEW AUTHOR AFFILIATIONS)
Summary
What is already known about this topic?
Highly pathogenic avian influenza A(H5N1) outbreaks have emerged in U.S. cattle and poultry. Wastewater surveillance detects influenza A(H5) subtype but does not currently distinguish between human and animal sources.
What is added by this report?
During September 15, 2021–July 11, 2024, retrospective analysis of wastewater surveillance data revealed 21 avian influenza A(H5) subtype detections across 12 Oregon communities. No association was found between detections in a community’s wastewater and history of a poultry outbreak or presence of dairy processing facilities or dairy farms within the sewershed. Avian influenza A(H5) was detected most frequently in two communities with important wild bird habitats.
What are the implications for public health practice?
Wastewater surveillance was an early indicator of avian influenza emergence in Oregon. Nonhuman and noncattle animal inputs, including wild birds, are an essential consideration when interpreting A(H5) subtype detections in wastewater.
Abstract
Wastewater surveillance is an important tool in the surveillance of emerging pathogens and has been leveraged during the highly pathogenic avian influenza (HPAI) A(H5N1) virus outbreak in cattle and poultry in the United States. Interpretation of avian influenza A(H5) subtype detections in wastewater requires an understanding of human and animal contributors to the sewershed because current testing does not distinguish between human and animal sources. Potential animal contributors include wild birds, farms with poultry or dairy cattle outbreaks, and dairy processing facilities. Retrospective analysis of 551 influenza A virus–positive wastewater surveillance samples from 20 sites in Oregon during September 15, 2021–July 11, 2024, revealed 21 avian influenza A(H5) subtype detections across 12 communities. Avian influenza A(H5) subtype detections in wastewater began approximately 6 weeks before Oregon’s first HPAI outbreak in domestic poultry, 7 weeks before Oregon’s first avian influenza A(H5) detection in wild birds, and 2 years before the first HPAI A(H5N1) outbreak in dairy cattle in the United States (Oregon has not detected HPAI A(H5N1) in dairy cattle or milk). No association was found between detection of avian influenza A(H5) in a community’s wastewater and history of an HPAI A(H5) outbreak among poultry in the county or presence of dairy processing facilities or dairy farms within the sewershed. Avian influenza A(H5) was detected most frequently in two communities with important wild bird habitats. Animal inputs, including from wild birds, should be considered when interpreting avian influenza A(H5) subtype detections in wastewater.
-snip-
Results
Regional Characterization
Among 551 influenza A virus−positive samples during September 15, 2021–July 11, 2024, 21 (3.8%) tested positive for the avian influenza A(H5) subtype (Figure 1) in 12 of 20 communities (Figure 2). The highest number of detections (five of 34) occurred in Ontario (Malheur County); the largest proportion of detections (three of 14) was in Newport (Lincoln County). Eight of 12 communities with avian influenza A(H5) subtype detections are within counties that previously had an outbreak of HPAI in poultry. Only four of 12 communities with avian influenza A(H5) subtype detections had a licensed Grade A dairy processing facility or dairy farm within the sewershed. The avian influenza A(H5) subtype was not detected in wastewater from the two sewersheds with the highest number of licensed Grade A dairy processing facilities (Portland [seven]) and Grade A dairy farms (Tillamook [13]). No association between avian influenza A(H5) subtype detections in wastewater and location within a county with a history of poultry outbreak (p = 0.65) or location of licensed grade A dairy processing facilities or dairy farms within the sewershed (p = 0.65) was identified.
Longitudinal Characterization
The avian influenza A(H5) subtype was detected during multiple weeks of each of the three influenza seasons during the study as well as during the summer of 2024 (Figure 1). The avian influenza A(H5) subtype was first detected in Oregon wastewater on March 21, 2022, approximately 7 weeks before avian influenza A(H5) was detected in wild birds (Figure 1) and approximately 6 weeks before HPAI was detected in poultry in Oregon (Figure 1).
Discussion
Wastewater surveillance in Oregon first detected the avian influenza A(H5) subtype on March 21, 2022, 6 weeks before HPAI A(H5) was identified in an Oregon domestic poultry outbreak, 7 weeks before avian influenza A(H5) was identified through Oregon wild bird surveillance, and 2 years before HPAI A(H5N1) was detected in dairy cattle in the United States (1). In this retrospective analysis, avian influenza A(H5) subtype detections in wastewater were not associated with poultry outbreaks or the presence of licensed dairy processing facilities or farms within the sewershed. Importantly, many avian influenza A(H5) detections occurred before the spillover of the virus into dairy cattle, estimated to have occurred during November 2023–January 2024,[SUP]¶[/SUP] and no HPAI A(H5N1) outbreaks in dairy cattle have been identified in Oregon (4). These results do not support poultry or licensed dairy farm or processing facilities as the etiology of the avian influenza A(H5) subtype in Oregon wastewater and suggest that noncattle animals, suspected to be wild birds, are a significant animal contributor to wastewater within the state.
Oregon is located along the Pacific Flyway, a major north-south route for migratory birds in the Americas that extends from Alaska to Patagonia. An estimated 1 billion birds traverse the Pacific Flyway yearly, and Oregon contains many important stopover sites (7). Animal input can enter wastewater via stormwater in combined (i.e., open) sewersheds or via leaking pipes within separate (i.e., closed) sewersheds, as well as through the dumping of animal products into the sewer system (6,8). Surveillance programs that sample from wastewater clarifiers might also capture excreta from wild birds that have been observed using clarifiers and lagoons as resting habitats. The two communities in Oregon with the most avian influenza A(H5) subtype detections contain important habitats for migratory wild birds, including seasonal wetlands (Ontario) and estuaries of major rivers (Newport) (7,9). Avian influenza A(H5) subtype detections occurred in both combined and separate sewersheds.
Limitations
The findings in this report are subject to at least two limitations. First, avian influenza A(H5) testing was performed retrospectively on samples that had tested positive for influenza A virus as part of Oregon’s routine influenza wastewater surveillance, which, before October 2023, occurred only during the influenza season. This approach limits the ability to describe seasonal avian influenza A(H5) subtype wastewater trends. Second, the testing methods used do not distinguish between animal sources or high- and low-pathogenic avian influenza A(H5) viruses (10).
Implications for Public Health Practice
The timing and spatial clustering of avian influenza A(H5) subtype detections in Oregon wastewater suggest that noncattle animals, suspected to be wild birds, are important contributors of the virus to Oregon’s wastewater. Oregon’s first avian influenza A(H5) subtype detections in wastewater did not occur until after the introduction of the 2.3.4.4b clade into wild birds in North America and preceded Oregon’s first HPAI poultry outbreaks and avian influenza A(H5) detections through wild bird surveillance by more than 6 weeks. The first avian influenza A(H5) subtype detection in Oregon wastewater occurred almost 2 years before the multistate outbreak of HPAI A(H5N1) in dairy cattle, excluding cattle as a potential source for subtype detections before November 2023. On the basis of the results of this retrospective study, continued intermittent detections of the avian influenza A(H5) subtype in wastewater are anticipated, even in the absence of outbreaks in dairy cattle or occurrence of human cases. Wild birds, in which HPAI A(H5) is now enzootic, are an important consideration when interpreting avian influenza A(H5) subtype detections in wastewater. Wastewater surveillance, with consideration of all animal contributors and in conjunction with other surveillance metrics, has the potential to strengthen ongoing avian influenza surveillance efforts.
https://www.cdc.gov/mmwr/volumes/74/wr/mm7406a5.htm?s_cid=mm7406a5_w