Influenza and RSV Report

The County of Santa Clara Public Health Department provides data to help you understand how respiratory viruses are spreading locally. These data are a resource for individuals and organizations to understand flu and RSV activity and take appropriate actions to protect yourselves and your communities. We provide these data during the respiratory virus season, which typically occurs October through the following May, but can fluctuate. 

How to interpret Public Health data dashboards

Watch this step-by-step guide for how to interpret data dashboards and virus trends in Santa Clara County.

Public Health uses several methods to monitor trends in influenza, or flu, and Respiratory Syncytial Virus, or RSV. We monitor the trends in concentration of influenza virus and RSV in the wastewater within Santa Clara County’s four sewersheds, reported emergency department visits due to influenza-like illness, reportable pediatric deaths occurring as a result of influenza or RSV, and type of influenza virus found in tested specimens.

The influenza and RSV wastewater dashboards are updated Monday – Friday during the respiratory virus season. Influenza Wastewater Dashboard data from 9/30/2023 to 1/14/2024 were adjusted on 2/21/2024 to reflect updates from academic partners.

All other dashboards are updated every Wednesday (excluding county holidays) during the respiratory virus season. Weekly data are preliminary and subject to change. 

For more information on Influenza and RSV, please visit:

Please click through each display on the dashboard and expand sections below to find more information.

    The County of Santa Clara Public Health Department provides an overview of RSV and Influenza A and B virus concentration in wastewater samples collected at wastewater treatment facilities that serve people in Santa Clara County. Four wastewater treatment facilities receive wastewater from designated geographic areas, known as “sewersheds,” within Santa Clara County. 

    Monitoring concentrations of RSV and influenza virus concentration in wastewater can detect levels of infection caused by RSV and influenza virus within a community.

    Source: Sewer Coronavirus Alert Network, or SCAN, project by Stanford University  

    RSV and influenza virus are shed in feces by individuals who are infected, both for individuals experiencing symptoms of influenza or RSV illness and for those who are infected but asymptomatic. This virus can then be measured in wastewater. 

    As is already the case for COVID, wastewater monitoring for RSV and influenza virus concentration is an accurate indicator to identify surges across the county. This is important because most RSV and influenza infections are not tested or reportable to the Public Health Department.   A higher concentration of RSV and influenza virus in wastewater has been demonstrated to indicate that more RSV and influenza are being transmitted locally. 

    Wastewater data isn't connected to a single household or even small neighborhoods. Samples are taken from water that combines the output of thousands of households. 

    Public Health is monitoring levels of RSV and influenza virus concentration in wastewater in partnership with Stanford University’s Wastewater SCAN Project. This effort includes all four wastewater treatment plant partners in Santa Clara County and builds on techniques developed during the COVID pandemic to track community virus transmission through wastewater analysis. 

    Wastewater samples are collected 7 days a week from all 4 wastewater treatment facilities within Santa Clara County. Results from the wastewater samples are available within 24 to 48 hours.

    The 4 wastewater treatment facilities collectively serve approximately 1,901,352 people, representing 98 percent of Santa Clara County’s total population.

    Wastewater samples are collected at the following wastewater treatment plants:

    Sewershed Wastewater treatment facility Approximate number of people in Santa Clara County served
    San Jose Santa Clara Regional Wastewater Facility 1,419,393
    Palo Alto Palo Alto Regional Water Quality Control Plant 215,544
    Sunnyvale Donald M. Somers Water Pollution Control Plant 161,021
    Gilroy South County Regional Wastewater Authority 105,394

    Source: U.S. Census Bureau, 2020 American Community Survey block data

    Santa Clara Regional Wastewater Facility serves people in the cities of San Jose, Santa Clara and Milpitas; Cupertino Sanitary District (City of Cupertino and nearby unincorporated areas); West Valley Sanitation District (Cities of Campbell, Los Gatos, Monte Sereno, and Saratoga); County Sanitation District No. 2-3 (unincorporated area); and Burbank Sanitary District (unincorporated area).

    Palo Alto Regional Water Quality Control Plant serves people in Los Altos, Los Altos Hills, Mountain View, Palo Alto, Stanford University, and the East Palo Alto Sanitary District. Note: A portion of wastewater received at the Palo Alto Regional Water Quality Control Plant comes from San Mateo County.

    Donald M. Somers Water Pollution Control Plant serves people in the city of Sunnyvale; Rancho Rinconada portion of Cupertino; and Moffett Federal Airfield.

    South County Regional Wastewater Authority serves people in the cities of Gilroy and Morgan Hill.

    Protocol for Sample Collection and Testing: Samples for testing consist of “settled solids” from wastewater entering each treatment plant. Samples are collected seven days a week from the wastewater treatment plants and are transported daily to a commercial lab for analysis. Laboratory staff process the samples to quantify Influenza A, Influenza B, and RSV concentration in the wastewater. These procedures use methods to concentrate solids and extract RNA and detect viral RNA. Results are typically ready within 24 hours of sample drop-off and are uploaded to this page. The quick turnaround is a major advantage of this data.

    Interpretation of Plots: Data reflected in the table below shows the results for Influenza A, and the concentrations are “normalized” by the concentration of a plant virus that is harmless to humans but is shed in stool. This plant virus is the pepper mild mottle virus, or PMMoV. Normalizing by PMMoV adjusts for changes in the amount of feces in the sample and the efficiency of the procedures from day to day.

    Wastewater typically contains waste from a variety of sources, such as from your shower or a commercial process. These types of waste do not have stool, the source of Influenza A, so they dilute the sample. Therefore, we adjust this sample to the known amount of feces in the wastewater to get an accurate result. 

    The curves displayed are the “5-day trimmed average” of the sample results. This is done by using samples from each day with the previous four days, eliminating the maximum and minimum among the five samples, and then taking the mean.

    This graph demonstrates the weekly percentage of total emergency department visits that are associated with influenza-like illness, such as fever, congestion, sneezing, sore throat, runny nose and cough, for each respiratory virus season, by week. 

    Source: ESSENCE, the Electronic Surveillance System for the Early Notification of Community-Based Epidemics. Facilities included in this dataset are Good Samaritan Hospital, Kaiser Permanente Santa Clara Medical Center, Kaiser Permanente San Jose Medical Center, O'Connor Hospital, Regional Medical Center of San Jose, St. Louise Regional Hospital, Stanford Medical Center, and Valley Medical Center.

    This graph demonstrates deaths due to influenza among individuals ages 0-17 years old and deaths due to RSV among individuals ages 0-4 years old. The data are presented by episode month, during the current respiratory virus season. Episode month is defined as the earliest of the following months, if available: month of onset, month of diagnosis, month of death, month of laboratory sample collection date, or month of report receipt. 

    Source: CalREDIE, the California Reportable Diseases Information Exchange

    This graph demonstrates the number of samples collected during this respiratory virus season that tested positive for influenza. It further indicates the number of samples that tested positive for Influenza Strain A or Influenza Strain B.

    Samples from PCR tests, rapid tests, and doctor’s office influenza tests for Santa Clara County residents and individuals with unknown residency data tested in Santa Clara County are counted in this graph. Limitations for this graph include potential missed influenza cases tested by alternate laboratories in the county or missed cases of Santa Clara County residents who are tested outside of the county.

    Sources: Santa Clara County lab testing sources include Stanford Health Care, Sutter Health/Palo Alto Medical Foundation, O'Connor Hospital, Santa Clara Valley Medical Center, and St. Louise Regional Hospital. Samples collected by other laboratories within Santa Clara County are not included in this graph.

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