A study of wastewater is showing that the SARS-CoV-2 virus, which causes COVID-19, is skyrocketing in Santa Clara County, according to online data from the county Public Health Department.

The virus is found in human waste that's made its way to wastewater treatment plants. Researchers from Stanford University have been sampling the wastewater at four plants in Palo Alto, San Jose, Sunnyvale and Gilroy. The sampling measures the quantity of two pieces of the virus known as its N and S genes, which are taken from the virus' ribonucleic acid, or RNA, which is a nucleic acid present in all living cells.

Recent testing shows a significant rise in these genetic components as the county and state are seeing a dramatic increase in COVID-19 cases attributed to the virus' more contagious delta strain. The amount of virus in the wastewater has tripled, and in some cases quadrupled, since June 16, indicating a much higher rate of infection throughout the county.

Significantly, the virus volume has spiked in recent weeks, according to online data from the county Public Health Department. The genetic material collected from the Palo Alto Regional Water Quality Control Plant has doubled in the past two weeks, according to county data, with the steepest climb starting on July 21.

The plant serves the municipalities of Los Altos, Los Altos Hills, Mountain View and Palo Alto, Stanford University and the East Palo Alto Sanitary District (in San Mateo County) and processes the waste of 213,968 residents, according to the county data dashboard.

The San Jose-Santa Clara Regional Wastewater Facility, which serves 1,458,017 residents in San Jose, Santa Clara, Cupertino, Saratoga, Milpitas, Campbell, Los Gatos and Monte Sereno, showed a similar rise over the last two weeks. It peaked on July 23, showed a decline on July 24 and has been climbing again through July 26, the last date of available data.

The volume of the virus in Sunnyvale has taken a wild ride, steeply rising and dipping throughout the past six weeks. It rose sharply around the July 4 holiday, based on samples collected from the Donald M. Somers Water Pollution Control Plant, which serves 169,000 residents. The virus tripled to its highest level in the period from July 14 to July 23 before leveling off. It began to drop on July 27, according to the data.

At the Gilroy-South County Regional Wastewater Authority, which serves 110,338 people in Morgan Hill and Gilroy, the virus amounts rose more slowly until it hit a steeper rise on July 11. The amount of virus leveled off and stayed relatively stable until July 21 when it also began to nearly triple, according to the county data. Like Sunnyvale, the amount of virus began to decline on July 26, but it is too soon to tell if the numbers represent a meaningful trend.

The samples are collected daily and are taken to a commercial lab for analysis. The results are usually ready within 24 hours after the samples are dropped off. The quick turnaround and posting is one of the major advantages of utilizing this data, according to the public health department.

Michael Balliet, deputy director of public health, said the data is tracking well with other sources of data.

"It really does a good job and gives us a broader perspective of what's going on in the community. It's particularly helpful if testing rates decline," he said, referring to the testing of individuals for the virus.

The county can compare the wastewater data with other metrics it gathers to understand trends. The staff looks for commonalities, but divergent data can also be helpful.

"We haven't seen major increases in emergency room visits as we have in the wastewater data," which could indicate that fewer people are making their way to the ER, he said. He stopped short of attributing the discrepancy to the effectiveness of the vaccine, however.

The county is continuing to examine trends related to holiday gatherings that attract many people, he said. The wastewater studies can prove to be valuable indicators of those trends.

All of the steepest rises in the past six weeks began about a week to 10 days after the July 4 holiday weekend, with the exception of Gilroy, according to the data.

Balliet noted that although the current spike is concerning, data going back as far as Oct. 1, 2020, shows it is, so far, much smaller than at the peak of winter's deadly acceleration. The virus' genes were at the highest concentration in December 2020 through early January 2021, which correlated with high rates of hospitalizations.

The study is led by Stanford's Department of Civil and Environmental Engineering and includes researchers from the Joint Initiative for Metrology in Biology at SLAC National Accelerator Laboratory Stanford, the Stanford University School of Medicine Department of Genetics, the Monterey Bay Aquarium Research Institute and the University of San Francisco Department of Engineering.

Unlike other studies that focused on liquid components of the wastewater, the Stanford study, which looked at the solids, found a greater concentration of the genes, the Stanford researchers wrote in an early paper in the Dec. 7, 2020, journal Environmental Science & Technology.

The sewage data is available online at covid19.sccgov.org/dashboard-wastewater.