A number of cities across the country have been using regular testing of sewage to spot genetic signs of COVID-19 and other diseases. The process, called wastewater surveillance, gives municipalities an edge in responding to upticks before they become widespread public health emergencies. A report recently issued by the National Academies of Sciences Engineering and Medicine outlines how this system could be deployed at the federal level to form a nationwide early warning system for diseases.
Drexel University College of Engineering LD Betz Professor of Environmental Engineering Charles Haas, PhD, a member of the National Academy of Engineering and noted expert on the movement of pathogens in the built environment, who co-authored the report, has been studying wastewater surveillance for some time and suggests that it could be a useful strategy for disease mitigation beyond the COVID-19 pandemic. Haas recently shared his insights on the challenges, possibilities and promise of wastewater surveillance with the Drexel News Blog.
How did the concept of testing wastewater as a public health tool to detect emergent diseases come about? How has it been previously deployed?
In the late 1930s, researchers at Yale University were first able to show the detection of poliovirus during an outbreak in urban wastewaters. Since then, it has been used for polio detection and monitoring of other disease organisms in sewage. With COVID-19, as early as March 2020, there were groups showing that the virus could be detected in wastewater in Brisbane, Australia, the Netherlands and Arizona. These latter studies indicated detection could often occur prior to the clinical observation of increased or detectable cases.
Why is it an effective method for early detection of upticks in diseases?
Detection of disease by clinical monitoring requires individuals to recognize a potential illness, seek medical attention and get necessary laboratory tests — which may take time. With COVID-19, more and more people are self-diagnosing with at-home tests — which are rarely reported into the health system — so we only recognize a portion of cases, and then perhaps with a lag. However, it has been clear that excretion of viral fragments can occur very early in the infection, and even in people who do not have symptoms. And since everyone provides an input to the wastewater stream, it does not rely on voluntary health care seeking behavior.
What are its limitations?
It does require laboratory capabilities and skills that may not be universally available at present. Often, public health agencies do not have the requisite experience and knowledge regarding waste sampling — and the functions of public health and wastewater management may be in different agencies, or even in different government entities. There is a significant fraction of the population in the U.S. not on centralized sewer lines, but often on septic tanks or non-community systems — these are often in rural areas and low-resource communities. So, trying to account for prevalence in the entire U.S. using wastewater surveillance testing would be difficult.
How is it currently being employed across the U.S.? How is Philadelphia using it?
There is a bit of a patchwork system at present. The Centers for Disease Control and Prevention has established a network, called the National Wastewater Surveillance System, organized via state and local health departments, to collect, analyze and report samples. There are also agencies contracting for surveillance with private companies and receiving foundation and private funding for sampling. Utilities around the U.S. have begun sampling, some as early as early 2021.
Philadelphia started in April 2022, and has its own summary of data (“dashboard”) online. There is a group at University of California, Merced that has aggregated many of the available dashboards, and the CDC has an aggregate site for the NWSS data.
What would need to happen to scale it up so that it could be a nationwide early warning system?
Several things. Much the same way as one would design a political opinion survey to be representative, we need to intentionally design a national wastewater network to be representative. We also need to account for the population not on central sewers.
There may also be targeted sampling of locations that are known or suspected hotspots, or that could serve as sentinels — or entry points — for imported strains entering the U.S., such as international airports.
We need to build up laboratory capacity — both facilities and human — to handle the new samples. If utilities sample within subsystems of their network, as some have — on a neighborhood scale, for example — there needs to be deliberate and intensive communication with the stakeholders to provide assurance and obtain support.
Media interested in speaking with Haas should contact Britt Faulstick, firstname.lastname@example.org or 215.796.5161.