The Nitty and Very Gritty of Wastewater Disease Monitoring

Medscape

a day ago

It didn't smell as bad as I thought it would. Sort of like going-bad ocean water but without the salt. It doesn't look as nasty as I thought, either, but it's important to maintain a sense of professional clinical distance even though I'm seeing and smelling the sewage of half a million people.
Here's how this works: Every night in Chester, Pennsylvania, a Philadelphia suburb, an operator dons a white hard hat, heads outside, climbs a flight of metal stairs, and walks across a bridge above a tank of dirty, gurgling water. They enter a small shed-like structure and retrieve a large plastic jug from a refrigerated cabinet. The jug is filled with sandy brown untreated wastewater freckled with tiny, dark brown lumps that sink to the bottom.
Wastewater flows toward treatment tanks at a facility near Philadelphia
The wastewater flowing into this facility goes through a series of carefully coordinated steps — grit removal and primary settling, microbial digestion, clarification, disinfection — to transform it into clean water. How clean? Well, by the time it reaches its ultimate destination, the nearby Delaware River, this water is cleaner than what's in the river already.
But this particular water jug, which contains samples collected at 15-minute intervals throughout the day, is going to the plant's in-house lab.
A sample of untreated water is collected from this temperature-controlled unit each day
An employee will gently shake the jug, mixing the solids and liquid within, and pour off samples into two 500-mL plastic bottles. Then they will carefully package, label, and seal the bottles and ship them to WastewaterSCAN, a nationwide tracking system based at Stanford University, Stanford, California, in partnership with Emory University, Atlanta, that tests wastewater for 11 infectious disease indicators.
Treated water, left, compared to untreated water, right
A vial of dirty water might be one of the most important tools in modern epidemiology. One simple reason, and it echoes the title of the classic children's book: Everybody poops .
Samples are prepared for shipping to WastewaterSCAN
'Wastewater is so incredibly powerful because we don't have to do anything — the default is opt in,' said Lauren Stadler, PhD, an associate professor of civil and environmental engineering at Rice University, Houston, and a co-lead of Houston Wastewater Epidemiology. 'We just go around our daily normal business, and everyone's contributing to this sample, and it's so unique in that way in that it represents this aggregate of everyone that's contributed to the waste stream.'
The Valuable Information We Flush Down the Toilet
Scientists have explored viruses in wastewater for decades, but the technology went mainstream during COVID-19. 'At the beginning of the pandemic, there was a huge effort to see if we could use wastewater to monitor SARS-CoV-2 because there was limited testing available and different test-seeking behavior and access to testing,' said Alexandria Boehm, PhD, Richard and Rhoda Goldman professor in environmental studies at Stanford University and principal investigator at WastewaterSCAN.
It turned out that infected people released SARS-CoV-2 RNA into wastewater in measurable amounts. 'I think we were all really surprised that we could use wastewater to figure out trends in disease occurrence, levels of disease occurrence and also the emergence of variants,' said Boehm. 'That was a huge surprise, and something that had never been done before.'
To check wastewater for disease surveillance, scientists use polymerase chain reaction (PCR) to detect and quantify RNA or DNA. That genetic material enters wastewater through our urine, feces, blood, saliva, skin cells, phlegm, anything we flush down the toilet or scrub from our bodies in the shower or sink.
Viral RNA is hardy enough to withstand its miles-long journey through pipes, tumbling alongside the other muck flowing through the sewer system. 'We've rubbed some wastewater on a surface in our lab, inside of a hood, let it dry and come back 10 days later and sampled it again, and we still get a lot of SARS-CoV-2, or at least half of it, so it's pretty robust,' said Jordan Peccia, PhD, Thomas E. Golden, Jr. Professor of Chemical and Environmental Engineering at Yale University, New Haven, Connecticut.
PCR can detect a wide range of germs in wastewater. WastewaterSCAN tracks COVID-19, influenza A, influenza B, respiratory syncytial virus (RSV), human metapneumovirus, enterovirus D68, norovirus, candida auris, hepatitis A, and two clades of mpox in wastewater.
When the WastewaterSCAN team receives a sample from one of its nearly 150 partner sites, they remove the solids — food particles, fecal particles, and everything else we flush and forget — from the liquid. That solid sludge is where the viruses live. Next, they extract the viral nucleic acids and place them in a droplet digital PCR machine equipped with primers and probes specific to the target they're looking for. They press start, and a PCR thermocycler machine generates amplicons, or pieces of RNA, if the target is detected. The team converts the numbers into units of copies per gram solids of the wastewater and then shares the data to their online dashboard.
The CDC gathers PCR testing data for COVID-19, influenza A, RSV, and mpox from 879 sites participating in its National Wastewater Surveillance System. Some states and municipalities have their own systems, too.
To see which infections are rising and falling in your area, you can check the WastewaterSCAN or CDC maps, or in some communities, your local public health department's website. You'll see peaks and valleys, but these maps can't tell you how many people are infected in each place. We don't yet know how much virus in wastewater equals one infection. Such a calculation would require more data on how many viral particles the average person sheds from body fluids when they're sick — data that is surprisingly scarce. Boehm hopes future research can address these questions.
'Having information on human shedding of these viruses will actually allow us to gain more insight into maybe how many people are sick or shedding the virus,' said Boehm. 'Right now, we can only say the trend is increasing, there are more people getting sick, or levels are very high now compared to before, so there are more people sick now than before, but we can't say it seems like maybe one out of 100 people have the flu.'
Still, the trends reveal a lot.
A Treasure Trove of Data
Here's how some healthcare providers and patients are using wastewater intel to promote public health:
Aiding clinical decision-making and situational awareness. Doctors have told Boehm they find wastewater data useful for clinical decision-making. 'I've also heard people say that they call it situational awareness, as a healthcare provider or public health professional, having a sense of what is happening in the community right now, so that when people present with different symptoms, there is this background knowledge of what is circulating and what might be going on,' said Boehm. For example, say a patient presents with flu-like symptoms. If influenza levels are high, a healthcare provider might consider flu testing and prophylaxis. If flu levels are low and human metapneumovirus levels are high, they might suspect the latter virus instead. 'Although each patient individually is different, this will never replace the care that an individual patient needs, especially someone who's severely ill, but it can help with situational awareness,' said Boehm.
Considering wastewater data when staffing and supplying healthcare facilities. Some hospitals adjust their schedules and supply orders when disease levels start ticking upward, said Helena M. Solo-Gabriele, PhD, a professor of engineering at the University of Miami, Coral Gables, Florida. During the height of the COVID-19 pandemic, her team shared wastewater data with a local health system to help them model staffing and supply needs.
Reducing the need for routine testing during outbreaks. Solo-Gabriele's team at the University of Miami found that wastewater monitoring could help reduce the frequency of clinical testing needed to monitor the spread of COVID-19 on college campuses. 'The good thing about it is that it's one sample or a series of samples that can represent thousands of people,' said Solo-Gabriele. Wastewater sampling could be particularly valuable in detecting rising levels of infections that are often asymptomatic or stigmatized. 'Some diseases, such as monkeypox, for example, have a stigma associated with them,' said Solo-Gabrielle. 'People may intentionally not go to the doctor or may intentionally not report it for concerns of being stigmatized, and so the wastewater gets around all of those issues that rely on people being diagnosed.'
Keeping schools healthy. Stadler and Houston Wastewater Epidemiology collaborate with about four dozen schools in the Houston area to monitor schools' wastewater for flu, COVID-19, RSV, and vaccine-preventable diseases like measles. 'If we have a detection of, for example, RSV or flu in the wastewater, if you're a parent who subscribes to the text alert system, you get a push notification being like, there's a there's RSV in your school — here's what you can do about it,' she said. If flu is detected multiple weeks in a row, the health department offers free, optional vaccines at the school. Parent feedback has been overwhelmingly positive.
Reprioritizing healthy habits. Once people know infections are increasing in their school, neighborhood or community, they might mask up or wash or sanitize their hands more often, said Solo-Gabriele. 'If we have rapid, accurate ways to know when an outbreak is going on, it can inform people for all sorts of things, from holding events for people who are immunocompromised to just thinking about being careful in your classroom if you're a teacher,' said Peccia.
Monitor new (or newly resurrected) viral outbreaks. In Houston, Stadler's team has been monitoring the city's wastewater to mitigate and prepare for a potential outbreak of measles. Boehm's team is working on technology to monitor bird flu.
Pinpoint hotspots before infections spread. When researchers at the University of Nevada, Las Vegas (UNLV) sampled wastewater from airports and other spots frequented by tourists, they found viruses early — before they showed up at the main wastewater treatment plant.
'As we increased that resolution and got closer to some of these locations, we realized that the near real-time intelligence that we could get could mirror what we were seeing at the clinical case level, and if not predict much earlier, what we were going to see at the clinical case level, and especially at the zip code level,' said Edwin Oh, PhD, a professor in the UNLV School of Medicine and College of Sciences.
Tourists are good at spreading germs — so are college students. Oh's team has detected chlamydia and gonorrhea in wastewater around the UNLV campus to help the student health center prioritize where on campus to offer free testing or provide information about these diseases.
'These are such treatable conditions, and perhaps because such testing is a cost, or is a cost associated with a parent's insurance, that such diseases, such infections, will be overlooked,' he said. Wastewater can provide intelligence and encourage service in areas that need it most, he said. The goal isn't to police behavior — it's to share information and provide choices. Wastewater data isn't traceable to individuals.
The Future of Wastewater Monitoring
Researchers are working on ways to extract even more useful information from wastewater. Someday, the benefits could extend to: