The future of disease tracking is heading down an unconventional route - through our wastewater. With the successful detection of the coronavirus and its variants in sewage, scientists are now exploring the potential of monitoring various health threats by analyzing our collective waste.
Before the COVID-19 pandemic, wastewater surveillance was a niche field, mainly focusing on testing for drugs or studying microbial ecosystems. Researchers were typically tracking specific health threats in specific locations, such as monitoring opioids in parts of Arizona or tracking polio in Israel. However, the pandemic changed everything.
The pandemic prompted an unprecedented surge in wastewater science. Adam Gushgari, an environmental engineer previously involved in opioid wastewater testing, now works on numerous wastewater surveillance projects at Eurofins Scientific, a global laboratory testing and research company. He describes the transformation as an "incredible acceleration," where what was once a small group of specialists has grown into a sizable community of scientists from diverse fields, including environmental science, analytical chemistry, microbiology, epidemiology, and more. They are all collaborating to track the coronavirus, interpret data, and share results with the public. As other COVID-19 monitoring methods decline, wastewater surveillance has become a primary source for identifying new surges.
Across the United States, hundreds of wastewater treatment plants have joined COVID-19 testing programs, contributing data to the National Wastewater Surveillance System (NWSS), established by the U.S. Centers for Disease Control and Prevention (CDC) in fall 2020. Hundreds more such programs have emerged globally, as monitored by the COVIDPoops19 dashboard at the University of California, Merced.
Over the past year, wastewater scientists have started to contemplate the broader possibilities of this infrastructure. They are investigating seasonal diseases like the flu, emerging diseases like bird flu and monkeypox, as well as drug-resistant pathogens like Candida auris. Researchers are even pondering ways to identify entirely new health threats.
Amy Kirby, a health scientist at the CDC who leads NWSS, predicts that wastewater surveillance will have health impacts extending well beyond COVID-19.
However, transitioning from potential to reality poses challenges. So far, sewage surveillance has primarily served as a proof of concept, validating data from other tracking systems. Experts are still figuring out how to translate data from wastewater into actionable policy decisions, even for COVID-19, which has been the flagship application of this monitoring method. They also face skepticism from public officials regarding its value and concerns that funding may dwindle now that the COVID-19 health emergencies have receded.
Mariana Matus, co-founder of Biobot Analytics, a company that has conducted sewage testing for the CDC and numerous health agencies, hopes that wastewater monitoring will continue to evolve and become a permanent technology post-pandemic. However, she acknowledges that this will require sustained support from governments, research institutions, and the public.
How Wastewater Testing Works
Wastewater-based epidemiology has a long history, dating back to John Snow's observations in the 1850s linking cholera outbreaks in London to contaminated water. In the 1920s and '30s, scientists began taking sewage samples and isolating specific pathogens causing diseases like polio and typhoid.
Today, automated machines collect sewage samples. These machines, whether they fit under maintenance hole covers or larger versions used at wastewater treatment plants, can be programmed to retrieve sewage at regular intervals. Depending on what scientists are testing for, the collected samples undergo various processes, from filtering out particles and extracting specific chemicals to using spectrometers to measure chemical concentrations. For detecting viruses like SARS-CoV-2, centrifuges separate liquid waste from solid waste, viral genetic material is isolated, and PCR machines, similar to those used for nasal swabs, test the results. Identifying specific SARS-CoV-2 variants can involve machines that identify different genetic sequences.
Validating the Virus in Wastewater
In the early days of the pandemic, a critical question loomed: Would the coronavirus even show up in wastewater? While diseases like polio spread through fecal matter, it was initially unclear if the primarily airborne coronavirus would appear in sewage.
Marlene Wolfe, an environmental microbiologist at Emory University, and her colleagues received a grant in 2020 to investigate. They began collecting sewage samples across the San Francisco Bay Area. Not only did the samples test positive for the virus, but the levels of coronavirus in wastewater mirrored trends in reported cases. As case counts rose, more virus was found in sewage, and vice versa. Similar results emerged in other regions.
Today, as traditional COVID-19 testing becomes less reliable, wastewater trends serve as a vital proxy for early warnings of potential surges. This has become particularly important as more people rely on at-home tests with unreported results.
Expanding the Scope
In the summer of 2022, wastewater tracking faced another test with the rapid global spread of mpox, a disease primarily transmitted through intimate contact between men. Tests for mpox were limited, and the disease carried social stigma, making people hesitant to seek medical care.
Within a few weeks, researchers, including Wolfe's team, developed tests to identify mpox in sewage. As with COVID-19, wastewater results closely aligned with official case numbers, even suggesting that the disease had spread farther than indicated by doctor's office data. This demonstrated the potential of wastewater technology to track various diseases, regardless of their mode of transmission.
Scientists are now discovering more infectious diseases that can be tracked through sewage. Nearly all the pathogens deemed important for public health have been identified in wastewater, stool, or urine, according to an informal literature review by Biobot. These pathogens range from the chickenpox virus to sexually transmitted disease-causing microbes like chlamydia to tickborne bacteria causing Lyme disease.
Determining What to Track
With so many possibilities, researchers are grappling with the question of what to prioritize. A report from the National Academies of Sciences, Engineering, and Medicine in January proposed three criteria: the pathogen should threaten public health, be detectable in wastewater, and generate data for public health agencies to protect communities. The first two criteria leave a broad field, so researchers are taking cues from local health officials on which pathogens to focus on.
Biobot is developing tests for common diseases like the flu, RSV, hepatitis C, and gonorrhea. The CDC is eyeing similar common pathogens and strategies for tracking antimicrobial resistance, which has risen during the pandemic.
Utilizing the Data
While tracking pathogens is a crucial step, translating results into actionable information is a challenge. Even with years of detailed data for COVID-19, many health officials hesitate to make policy decisions based on sewage data. The traditional approach in public health is centered around identifying individual sick individuals and tracing how they got infected. Wastewater surveillance, in contrast, aggregates data from thousands of individuals and relies on environmental factors, making it less intuitive to interpret.
Environmental factors like weather, local industries, and tourism can create outliers in sewage data. For instance, heavy rain can dilute samples, and industrial runoff can affect analytical methods. Each pathogen's data must be interpreted differently.
For example, with coronavirus data, researchers look for trends as viral concentrations rise or fall. A spike might indicate an impending surge, prompting the community to allocate more health resources, such as vaccine clinics, mask distribution, or hospital staff reinforcement.
Mpox, on the other hand, requires a different approach. Since it infects fewer people, sewage testing focuses on monitoring its presence or absence, serving as an early warning system.
Interpreting data for pathogens
like C. auris, a drug-resistant fungus, is more complex. While early detection could guide public health actions, C. auris can grow in sewage after leaving healthcare facilities, potentially leading to data misinterpretation.
Shaping the Future
Some scientists envision a proactive approach, using wastewater monitoring to detect new health threats early. For instance, researchers in Ireland are interested in screening sewage for the H5N1 bird flu. Another approach involves broad genetic testing of sewage to identify new pathogens before they cause outbreaks, although this requires further research.
However, before proactive surveillance can become a reality, basic standards and protocols for wastewater data usage must be established. The field needs to grow further, with more sites contributing data and more scientists analyzing it. Sustained funding is essential for this to occur.
The CDC's wastewater surveillance program, funded through COVID-era legislation, faces a funding gap by 2025. While wastewater surveillance is cost-effective compared to other testing methods, it still requires substantial resources. For example, Washington state's health department paid over $500,000 to Biobot for a one-year sewage testing contract, and the CDC has allocated over $23 million to the company for NWSS since 2020.
In recent years, wastewater surveillance has evolved from a niche endeavor to a global collaboration, with scientists across disciplines exploring the potential of sewage data for public health. While many questions remain, it is clear that wastewater monitoring holds promise as a powerful tool for tracking collective health.
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