What Silicon Valley’s Sewers Reveal About the Coronavirus

Epidemiologists are doing the dirty work.

As coronavirus infections skyrocket throughout the nation, scientists are studying the foul sludge coursing through thousands of miles of sewage pipes in Silicon Valley to identify outbreaks before they’re reflected in official case counts.

Recent analysis from that effort confirms what experts have been warning us about on a daily basis as the South Bay surpasses 50,000 cases—a milestone that brought Santa Clara County Public Health Officer Dr. Sara Cody to tears earlier this week. The present surge in Covid-19 infections is far more serious than the waves that prompted sweeping shutdowns this past spring and summer. And it’s about to get worse.

Because the virus can be found in human stool, even from people without symptoms, a team led by Stanford University has been regularly testing wastewater in San Jose, Santa Clara, Palo Alto, Sunnyvale and Gilroy to reveal local trends of disease spread.

What researchers determined is that as virus levels rose in the region’s wastewater, so too did the number of reported cases. The past month of sewage data shows a sharp uptick that tracks with diagnostic trends from nasal swab tests.

On Tuesday, county Environmental Health Director Michael Balliet briefed the Board of Supervisors about the project, pointing to charts illustrating viral detection from the San Jose-Santa Clara Regional Wastewater Treatment Plant, he noted how coronavirus levels “really skyrocketed” in early November.

“It has taken off,” he told the five-member county board, “which again indicates widespread infections in the community.”

On Thanksgiving Day, researchers saw the highest levels to date—a trend that has continued its upward ascent in the weeks since.

“It continues to be a high, high, high level detected in wastewater,” Balliet said during his presentation, “which is very concerning because it’s orders of magnitude greater than where we were at—even in the June timeframe.”

Stanford’s wastewater analysis reflects a national trend of looking at sewage as a more comprehensive, cost-effective way of monitoring the virus.

Just last month, the federal government took some significant steps to implement wastewater epidemiology more broadly.

On Nov. 27, the U.S. Departments of Health and Human Services and Centers for Disease Control (CDC) hired AquaVitas to run a study of up to 100 treatment plants in every state. The CDC is also calling on labs, treatment plants and local health departments to submit data as part of a national wastewater surveillance initiative.

“Wastewater-based epidemiology is not a new concept,” Balliet said, “but it is a concept that that has gained a lot of attention in the past nine months, for obvious reasons.”

Granted, there are limitations on the data, he noted, including the fact that the coronavirus rate of decay can make samples of stool less accurate over time. “Because it’s relatively new,” Balliet said, “procedures are evolving nationally.”

Even so, he added, “the data is really promising.”

Jennifer Wadsworth is the former news editor for San Jose Inside and Metro Silicon Valley. Follow her on Twitter at @jennwadsworth.


  1. The county supervisors, local officials, and even our governor did not have the guts to stand up the the pressure of special interest. Their political careers weighed much more than their duty to protect the people. The science was there and also the history to show us how significant this virus is and the harm that could cause. I used that knowledge and that of God. He sent this virus. History has also taught us some will never learn from this experience. This is a time to really preserve the health and lives of those we love and others. A living dog has more valué than a death lion (from Bible). This will be a dark Christmas and a darker New Year! This is God’s time. The virus is the sign in the earth and the Christmas star (December 21) the sign in the skies. This year is the year of the death of the many!

  2. I call B.S.
    Figures lie and Liars figure, but in the end, where are all the dead bodies?
    It’s a real disease, but it’s not a real pandemic.

  3. Wow you just said “figures lie and liars figure”! Let’s give you a Nobel prize in epidemiology, you know so much more than legions of scientists who have worked on this for their entire careers.

  4. Your article on Covid tracking through the San Jose sewage against actual outbreak numbers was fascinating, not to mention especially since it was dated January 29, 2021 which is tomorrow… a little odd as it’s only 6:51 PM PST as I write this on 1/28/21 :D

  5. Barb, that sewage epidemiology story ran on Dec. 17. Not sure where that Jan. 29 dateline is showing up for you.

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