Sewage testing can provide an early warning of rising COVID-19 cases in communities.
Likhitha Duggirala, BDS, MPH, explains how this new method is helping public health experts track the spread of the virus. As Epidemiological Surveillance Coordinator at the Nebraska Department of Health and Human Services, Duggiirala works directly with Nebraska’s wastewater surveillance program.
Duggirala says sewage testing helps public health experts in four ways:
- Monitor infections in the community. Wastewater monitoring does not depend on people having access to or obtaining COVID-19 tests.
- Follow trends in the community – is COVID-19 increasing or decreasing overall?
- Alert public health experts to act quickly. If cases increase, public health experts can recommend protections for their community.
- Screen a building or facility for COVID-19. For example, researchers at the University of Nebraska Medical Center used sewage testing to detect new COVID-19 infections in Omaha public schools that would otherwise have gone undetected.
Why is COVID-19 in wastewater?
Believe it or not, your poop contains clues to your health. “People infected with SARS-CoV-2 can shed the virus in their stool, even if they have no symptoms,” says Duggirala. Since everyone’s waste goes to one place – the sewer – public health experts can take samples and see the amount of COVID-19 in the community.
It is important to note that people do not come into contact with sewage and do not get sick that way.
How does the sewage test for COVID-19 work?
Teams from the University of Nebraska Medical Center, University of Nebraska – Lincoln, and Nebraska DHHS are working together to collect, analyze, and report the data.
- Sample collection: UNL researchers coordinate the logistics of sample collection. Researchers or facility operators take a sample from wastewater treatment plants, seal it, and send it to the lab. They pull a new sample from the same place every week. There are 15 locations in Nebraska where samples are being taken with plans to add more.
- Sample processing: The UNMC College of Public Health Laboratory receives and processes specimens. After preparing the sample, they extract the RNA (unique virus code) and measure the virus concentration in the wastewater.
- Data interpretation: Nebraska DHHS collects and interprets data from sewage treatment plants, UNL, and the UNMC College of Public Health. They process the data before sending it to the Centers for Disease Control and Prevention.
- Data report: The Nebraska DHHS publishes a weekly sewage monitoring report.
Everyone in the country uses a standardized CDC process for testing and treating wastewater.
How accurate are sewage COVID-19 tests?
Sewage analyzes are used as an additional method to track the spread of COVID-19. However, it is currently difficult to predict exact levels of community transmission of COVID-19 based solely on sewage testing.
So far, sewage analyzes correlate (or rise and fall) with official case counts, suggesting that sewage monitoring is reliable.
Because everyone poops — and not everyone tests — sewage testing can give a more complete picture than case counts.
The official case of COVID-19 counts the total number of underreported cases because:
- Home tests are not included in the official counts
- People with asymptomatic COVID-19 (no symptoms) are unlikely to get tested
- Lack of test accessibility remains a problem
- People don’t always seek testing when they’re sick, for several reasons
“In underserved communities, where testing and health care are less accessible, wastewater monitoring helps assess the burden of COVID-19 disease in the community,” says Duggiirala.
For greater accuracy, public health experts do not compare levels of COVID-19 from place to place. They only compare the levels of a location over time.
Will COVID-19 increase further?
Sewage analyzes monitor the spread of COVID-19, in addition to the number of cases and the number of hospitalizations. But hospitalizations are a lagging indicator — by the time someone has been hospitalized, it’s days or even weeks after they were exposed to COVID-19. It takes time for people to be tested and then for the numbers to come out.
In contrast, ongoing sewage testing for the community may be an early indicator of an increase in the spread of COVID-19. “Sewage monitoring can be a leading indicator three to six days in advance,” says Duggiirala. “It’s an alarm system. During the omicron surge, we saw virus levels in sewage monitoring increase before case rates increased.”
Below is the most recent wastewater monitoring data for Douglas County. You can see a slight uptick in the top chart with the red line. This means COVID-19 cases are likely increasing in Douglas County.
Source: Nebraska DHHS Wastewater Monitoring Report.