Central Valley Wastewater Data

Norovirus

Healthy Central Valley Together monitors wastewater for genetic markers of norovirus. Norovirus is a very contagious virus that causes vomiting and diarrhea. Noroviruses are transmitted primarily by direct person-to-person spread or via fecally contaminated food or water. People of all ages can get infected with norovirus and can shed billions of norovirus particles in feces.

We monitor norovirus in wastewater to assess trends in its prevalence in the community.  Lab tests detect if viral genetic material is present in wastewater solids samples analyzed three times each week. The lab determines the number of copies of norovirus RNA per gram of wastewater solids. The results are reported to public health officials in Merced, Stanislaus and Yolo counties and to the public. Disinfection treatment processes at wastewater and water treatment plants inactivate noroviruses.

We also measure a generally harmless virus called pepper mild mottle virus or PMMoV, which is a highly abundant virus in human waste. We use PMMoV in the laboratory as a process control to help correct for measurement-to-measurement variability. PMMoV can also serve as a measure of the “fecal strength” of each sample, which can change for factors like rain, water usage and industrial flow. Dividing (or normalizing) the quantity of norovirus RNA by PMMoV lets us compare results over time and from place to place. Over time you will see this value rise and fall, indicating more or fewer norovirus infections in the community served by each wastewater treatment plant.

We display comparable data for each location two ways. This heat map uses color coding to show how many viral genetic markers were found on each day a sample was tested. The darker the color on the heat map, the more copies of the virus gene we test for were detected (white spaces indicate days when samples were not taken). If you hover your cursor over a colored square, the actual data for that day will appear. Below the heat map are charts showing trends in our monitoring results for communities in the three Central Valley counties we partner with once we use PMMoV to control for variability. White spaces indicate days when samples were not taken, and light blue spaces indicate days when there was no detection of virus genetic material in samples.

You can see more results for each participating community on our pages for Merced County, Stanislaus County, and Yolo County. 

For the best experience in mobile, please view all charts in landscape mode.

In trend line charts, we display data that have been “smoothed” and “trimmed.” Each data point is a five-day average (smoothed) in which the highest and lowest result has been left out (trimmed). Because environmental samples like wastewater can fluctuate a great deal on a particular day, this average number allows us to see actual trends more easily.