(Sacramento)
The secret is in the sewage. As COVID-19 spreads, sewage testing has become a valuable tool in predicting local spikes in infections.
During the pandemic, health care facilities have been required to report COVID-19 cases to authorities, but the number of reported infections has fallen as more people are taking antigen COVID tests at home and keeping their results private.
Also, most people have developed some immunity through vaccination or past infection and are less likely to seek medical care, further reducing our ability to monitor community infection rates.
“At-home testing has undoubtedly made it harder to collect reporting data,” said Nam Tran, a professor and senior director of clinical pathology at the University of California, Davis, Health Department, “but tracking at the federal level changed even more dramatically last May when the pandemic emergency was declared over.”
That's because, according to chemical scientist Tran, the Centers for Disease Control and Prevention (CDC) no longer requires reporting of hospital-acquired COVID-19 transmission data as of May 1, 2024. The CDC encourages facilities to continue reporting voluntarily, and at the state level, several public health agencies still require some level of COVID-19 reporting for hospitals and work settings.
Increasing reliance on wastewater testing to determine community spread
In 2020, the CDC launched a nationwide wastewater testing program that has now expanded to more than 1,000 testing sites, including more than 30 in California. CDC works with local health departments to collect data.
According to the CDC, wastewater can include water used in homes and buildings, such as from toilets, showers, and sinks, as well as storm water and industrial runoff. The water is collected as it flows into a treatment plant, and samples are then sent to a public health or environmental lab for testing.
The CDC's tracking site allows you to search results by state. Nationwide, COVID-19 concentrations in wastewater are listed as “very high” as of the week ending August 17, with California having even higher concentrations than the national average.
“Wastewater treatment is a great new tool that's now become more mainstream because of the pandemic,” Tran said.
In this Q&A, Tran answers some common questions about wastewater tracking and why it's useful.
How does wastewater COVID monitoring work?
People infected with SARS-CoV-2 shed the virus in their stool even when they have no symptoms. Testing for the virus' genetic makeup can detect the virus in local sewage. This gives us a good sense that the organism is present. However, this is not a conclusive sign of active infection. For example, some diseases shed nucleic acid for a period of time but may not produce symptoms or be contagious. Another challenge is that when disease prevalence is low, it can be like searching for a needle in a haystack.
As the pandemic progressed and the utility of wastewater testing became clear, the tests have evolved to become more sensitive, and public health communities can now adapt the technology to detect other pathogens.
Wastewater is a great new tool that's now become more mainstream thanks to the pandemic. —Nam Tran, senior director of clinical pathology, UC Davis Health
How can health care providers and community leaders use wastewater data?
This provides trends and general indications of the likely presence of a microorganism within a community. So, for example, if there is an increase in the amount of a particular virus, it may indicate the burden and spread of a disease within the community. This allows health workers to plan, prepare, and keep an eye out for people showing symptoms of the disease.
However, it should be noted that this is a pooled sample and therefore reflects all influences that the population (including animals and the environment itself) has on the wastewater. Wastewater testing data is best used in conjunction with other information such as hospital admissions.
Why is wastewater testing for COVID-19 important?
Sewage testing can detect the virus, especially during times of rapid infection spikes, even when people are not reporting it by testing at home or seeking medical attention. This allows sewage testing to complement many of the tools used for public health surveillance.
Will wastewater testing be used to monitor other diseases?
Yes, it is being used to test for a variety of pathogens. Recently, this data has been used to track Influenza A, which may be a surrogate for the potential risk of HPAI (H5N1) spreading. The “SCAN Project” run by Stanford and Emory Universities is a good example of the types of testing being done, including influenza, RSV, COVID, norovirus, MPOX, and potentially non-communicable diseases in the future.
UC Davis Health is using this data to support what is being observed across clinics when it comes to respiratory illnesses like influenza, RSV and COVID.
What do you think about the future of wastewater testing?
Ultimately, the question becomes, what is the return on investment of tracking potential diseases? If we know a pathogen is spreading, will wastewater data be enough to stop its spread? Certainly, wastewater data increases our awareness and ability to plan, but these testing solutions can be expensive, so it remains to be seen what the long-term outcomes will be. As we learned in 2020, we can't test to rid ourselves of a pandemic; wastewater is just another tool to inform public health decision-making.
Related Resources and Stories
