US - California: Possible Flu A surge indicated by wastewater analysis in Palo Alto - July 2025

[sharon sanders]

hat tip @JusDayDa , @Nucleocapsoid , Michael Coston


I am not sure what to make of this. Apparently there was a flu A surge in the Palo Alto wastewater graph recently in July 2025. The published data speaks for itself. I also checked data from nearby waste treatment plants and none of them showed the Palo Alto anomaly. No HA type was identified in this presented data. It appears the levels are going down now. I guess we see.




“These data were collected as part of the WastewaterSCAN / SCAN project, a partnership between Stanford University, Emory University, and Verily funded philanthropically through a gift to Stanford University.” In addition, the following paper should be cited:

• A. B. Boehm, M. K. Wolfe, Amanda L. Bidwell, Alessandro Zulli, Vikram-Chan-Herur, Bradley J. White, Bridgette Shelden, Dorothea Duong. 2024. Human pathogen nucleic acids in wastewater solids from 191 wastewater treatment plants in the United States. Scientific Data, 11, 1141. Link to paper.

https://data.wastewaterscan.org/tracker/?charts=Ci0QACABSABSBjI1NDgxOVoLSW5mbHVlbnphIEF4jwSKAQZlYjk5MDK4ASTAAQE%3D&selectedChartId=eb9902

[sharon sanders]

from CDC -

Influenza A National Wastewater Data


Influenza A Wastewater Monitoring in the U.S.

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Nationally, the wastewater viral activity level for influenza A is currently very low. See influenza A data for your state/territory and county


On This Page

• Current Wastewater Viral Activity Levels
• National Trends
• What Does this Data Mean?
• About the Data

Wastewater monitoring can detect viruses spreading from one person to another within a community earlier than clinical testing and before people who are sick go to their doctor or hospital. It can also detect infections without symptoms. If you see increased wastewater viral activity levels, it might indicate that there is a higher risk of infection. See how to protect yourself from respiratory viruses.

Wastewater data are updated every Friday with the previous week’s data, which allows for data to be reviewed for accuracy. Data may change as more reports are received.

Current Wastewater Viral Activity Levels


This map shows the current wastewater viral activity level of influenza A for each state or territory. Tap or hover over a state or territory to see the viral activity level and number of sites reporting data. Time Period: July 13, 2025 - July 19, 2025

Skip Over Map Container U.S. territories

GUVI Influenza A Wastewater Viral Activity Levels


Select a level to add or remove from map.

• Very High
• High
• Moderate
• Low
• Very Low
• No Data
• *Limited Coverage

* Based on a small segment (less than 5%) of the population and may not be representative of the state/territory.
Data last updated 2025-07-24

Link to Dataset Download Data (CSV) Skip Data Table
Data Table Skipped data table.
National Trends


This chart shows national trends of wastewater viral activity levels of influenza A. 1 Year6 Months45 DaysAll Results Skip Over Chart Container
Very LowLowModerateHighVery High08/17/2409/28/2411/09/2412/21/2402/01/2503/15/2504/26/2506/07/2507/19/25Week Ending
Data from the most recent two weeks may be incomplete due to delays in data reporting. These data sets are subject to change and are indicated by the gray shading.

Data last updated 2025-07-24

Link to Dataset Download Data (CSV) Skip Data Table
Data Table Skipped data table.
What Does this Data Mean?


Situational Summary

• The ongoing avian influenza A (H5) (bird flu) outbreak in U.S dairy cows and poultry may be contributing to the moderate and high influenza (flu) A virus wastewater levels in some jurisdictions, based on reviewing multiple data sources. The risk to the public of avian influenza A (H5) is currently low.
• Wastewater data for influenza A virus should be considered in combination with clinical sources of influenza A data.
• Influenza A viruses include subtypes like avian influenza A(H5) virus and A(H1N1). Wastewater testing for overall influenza A virus cannot tell us what subtypes are present. Wastewater testing cannot tell us if the source of the influenza A virus is from humans, animals, or animal products.
• Wastewater testing for influenza virus subtypes, including an H5 subtype, is underway across the United States. See Wastewater Data for Avian Influenza A(H5) for more information.
• CDC and public health partners continue to investigate whether changing levels of influenza A virus in wastewater are related to seasonal influenza, the avian influenza A (H5) outbreak in animals, or both.

About the Wastewater Viral Activity Level: The wastewater viral activity level indicates whether the amount of virus in the wastewater is very low, low, moderate, high, or very high. The wastewater viral activity levels may indicate the risk of infection in an area. The wastewater viral activity levels are categorized as follows:

• Up to 1.6 – Very Low
• Greater than 1.6 and up to 4.5 – Low
• Greater than 4.5 and up to 12.2 – Moderate
• Greater than 12.2 and up to 20.1 – High
• Greater than 20.1 – Very High

National data represent the median values across all wastewater treatment plants. To learn more on how the wastewater viral activity level is calculated, see Data Methods.

Data Limitations: Wastewater data cannot determine the source of influenza A viruses. Detections could come from a human or from an animal (like a bird) or an animal product (like milk from an infected cow).

Related Pages

• Influenza A State and Territory Trends
• Wastewater Data for Avian Influenza A(H5)
• How Wastewater Monitoring Works
• CDC’s Wastewater (NWSS) Program
• About Wastewater Data

Source: Centers for Disease Control and Prevention

https://www.cdc.gov/nwss/rv/influenzaa-national-data.html

[sharon sanders]

Santa Clara county is showing very high in the tiny graphic from the CDC site:

https://www.cdc.gov/nwss/rv/InfluenzaA-statetrend.html?stateval=California

[SeniorLearner]

I accessed the WasteWaterSCAN site just now and noted that the Palo Alto CA site shows zero values for H1, H3, AND H5 assays over an extended time period, with values reported only for "Influenza A". Here is the link: WastewaterSCAN Dashboard I suspect they are not subtyping their positive results, which is quite unfortunate and likely due to budget or personnel constraints. California has had sporadic ongoing dairy outbreaks in-state, so H5 spillovers from milk-processing or disposal are possible, as are wildlife drainage issues into sewer sheds.

This is all speculative without more information on the subtyping results themselves and accompanying metadata from the sewer shed. With all the cuts to public health funding I have little faith that any of this will get better or make much sense in the short term. The best we can hope for is to keep a semblance of this infrastructure in place for revival and refurbishment when the big one hits, whether H5, another H-type, or another viral pandemic agent altogether.

[SeniorLearner]

OK, I went back to the site one more time after a day of stewing about what could be going on. I found a new way to display results which indicates that this site IS likely running the H1, H3, and H5 tests with negative results. Here is a screen shot of WastewaterSCAN Dashboard that shows those results over 2 years:

As you can see, H1 (and a bit of H3, which is hard to see in the copy) were present during last winter's "flu season". H5 was also prevalent, due to the milk residues in the sewage from the dairy cow and possibly the poultry outbreaks. It's theoretically possible that a few people could have been shedding H5 virus in wastewater, but medical surveillance did not really support that. Regardless, since early June, there have been NO H-types detected, although the influenza (matrix gene) readings have taken off.

More importantly, note that total Matrix Influenza levels have exceeded H1 plus H3 plus H5 for the entire time period, whenever significant influenza levels are present! This sewage catchment obviously captures influenza viral contamination from wildlife - birds?? And the H types are likely not H1, H3, or H5, which would be expected with endemic avian influenza. The "high influenza" findings in the Palo Alto catchment only reflect that wildlife (birds) are shedding avian influenza into the catchment, NOT that there is some nefarious influenza in northern California. Once again, some analysis of the catchment area properties AND subtyping / sequencing of the virus (should be easy with these peak levels) would add to the picture. As always, flu can reassort, so there is no such thing as a completely harmless flu in the environment.

In the event of a pandemic, it may be possible to sample in locations that avoid contributions from the wildlife sources. These readings are not a fatal flaw in environmental sampling, only another factor that must be addressed in interpreting results. Many "closed" sewage systems should have few issues with wildlife contamination.

Over-interpretation of results without the context of understanding the catchment is dangerous. If there is NOT a wild bird source in the Palo Alto sewage stream, then I have some more issues to understand!

[sharon sanders]

Agree. Thank you for your posts.

We do not warranty anything on FluTrackers. We post what we think is an interesting data point and then see if we can add substance based on facts as we can evaluate them. For instance, we publish many governments' disease reports. We do not think these are 100% correct or thorough. They give us a baseline only.

As to the wastewater data...well...I do not think they have been in use long enough to be validated. They are interesting but not definitive imho. I do not think they are a replacement for actual "hands on" disease surveillance procedures.

[Pathfinder]

County of Santa

H5N1 bird flu

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Last content update: 6/25/25

The County of Santa Clara Public Health Department recommends that people do not consume or feed their animals raw milk or raw milk products.

Multiple raw milk and raw pet food products have been recalled since December 2024 because they had the potential to be contaminated with H5N1. For more information, see announcements from the Food and Drug Administration (FDA) and California Department of Health (CDPH) on food and product recalls.

The County of Santa Clara Public Health Department is monitoring a multi-state outbreak of H5N1 bird flu in dairy cows that has led to cases in humans, primarily dairy and poultry workers.

To date, there have been no reported cases of H5N1 bird flu in cows or humans in Santa Clara County.
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https://publichealth.santaclaracounty.gov/diseases/h5n1-bird-flu

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Detections of Highly Pathogenic Avian Influenza in Wild Birds

Last Modified: July 28, 2025
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https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/wild-birds

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WastewaterSCAN Dashboard

Influenza A, Santa Clara, CA



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