Community wastewater holds clues about the burden of COVID-19. Over the course of the pandemic, wastewater monitoring has become an increasingly common method of trying to understand local infection trends.
Microbiologists Susan DeLong and Carol Willoch met and became wastewater enthusiasts in April 2020 when a popular group of wastewater treatment plant operators asked them to develop and deploy a test to detect SARS-CoV-2 in samples from Colorado sewers. De Long is an environmental engineer who studies beneficial bacteria. Willoch’s expertise in RNA biology. Here they describe how wastewater monitoring works and what it can do in the post-pandemic future.
How is wastewater monitored for SARS-CoV-2?
Wastewater monitoring takes advantage of the fact that many human pathogens and human drug metabolism products end up in the urine, faeces, or both. The SARS-CoV-2 virus that causes COVID-19 appears in surprisingly large amounts in the feces of infected people, although this is not a major route of transmission of the disease.
To find out if any pathogens are present, we first need to collect a representative sample of wastewater, either directly from the sewer or at the point where what engineers call “impact” enters the treatment plant. We can also use solids that have settled in sewage.
Technicians then need to remove the large particles from the stool and concentrate any microbes or viruses. The next step is to extract nucleic acids – the DNA or RNA that carries the genetic information of pathogens.
The sequences in DNA or RNA act as unique barcodes for the pathogens present. For example, if we detect genes unique to SARS-CoV-2, we know that the coronavirus is present in our sample. We use PCR-based approaches, similar to those used in clinical diagnostic tests, to discover and sequence SARS-CoV-2.
Characterization of DNA sequences in more detail can provide information about viral strains – for example, it can identify variants such as omicron BA.2.
Currently, the vast majority of wastewater control efforts focus on SARS-CoV-2, but the same methods work for other pathogens, including polioviruses, influenza, and norovirus.
Prior to the pandemic, one application was to monitor rare poliovirus outbreaks in areas where polio vaccination continues. Wastewater can also be monitored for signs of several drugs to give insight into the level and type of drug use among the population.
Where does the data go?
During the pandemic, the US Centers for Disease Control and Prevention developed the National Wastewater Surveillance System specifically to track SARS-CoV-2 across the country. Over 800 sites submit data to this NWSS system, but not all states and territories are currently represented.
Many state agencies, such as the Colorado Department of Public Health and Environment, and cities, such as Tempe, Arizona, have their own dashboards for reporting data. Some companies that perform wastewater analysis report the data on their dashboards as well.
In our opinion, the NWSS represents an exciting first step in monitoring population health through wastewater. Similar systems are being established in other countries, including Australia and New Zealand.
What does wastewater data really show?
SARS-CoV-2 levels in wastewater from large populations are an excellent indicator of the level of infection in a community. The system automatically monitors everyone who lives in the sewers, so it’s anonymous, unbiased and fair. Importantly, it is also impossible to trace the infection to a specific person, home, or neighborhood without additional sampling.
Wastewater monitoring does not depend on the availability of clinical tests or on the people who report their test results. It also captures asymptomatic or asymptomatic COVID-19 cases; This is critical because people who are infected but don’t feel sick can still spread COVID-19.
In our opinion, wastewater testing is becoming increasingly important as more COVID-19 tests are being done at home. And because vaccination has also led to more mild and asymptomatic cases of COVID-19, people may become infected without ever getting tested. These factors mean that clinical case data are less informative than they were earlier in the pandemic, while wastewater data remain a consistent indicator of the level of infection in a community.
So far, you cannot accurately predict the number of infected individuals in a community based on the level of virus in the wastewater. A person’s stage of infection, how their body responds to the virus, the viral variant, how far away a person is from where the wastewater sample was taken, even the weather can all affect the amounts of SARS-CoV-2 measured in wastewater.
But scientists can infer relative changes in infection rates. Watching viral levels rise and fall in wastewater provides a glimpse into whether cases are rising or falling in the community as a whole.
Because SARS-CoV-2 can be detected on wastewater days or even weeks before outbreaks occur, wastewater monitoring can provide early warning that public health measures may be necessary. And the directions in the signal are important –If you know the levels are going upIt might be a good time to recreate the mask mask or recommend working from home. Currently, public health officials use wastewater monitoring data along with other information such as test positivity rates, the number of clinical cases, and hospital admissions in the community to make these types of decisions.
Data from sequencing can also help discover new variants and monitor their levels, allowing healthy responses to take into account characteristics of an existing variant.
In smaller populations, such as in college dormitories and nursing homes, sewage monitoring can detect a small number of infected people. It could raise the alarm that targeted clinical testing aims to identify infected people for isolation. Early detection, targeted testing and quarantine are effective in preventing outbreaks. Instead of using clinical tests for routine monitoring, officials can reserve disruptive clinical tests for the times when SARS-CoV-2 is detected in wastewater.
What will surveillance look like in the future?
The widespread and routine use of wastewater monitoring would give public health officials access to information about levels of a range of potential infections in American communities. This data can guide decisions about where to provide additional resources to communities, such as conducting testing or vaccination clinics in places where infections are increasing. It can also help determine when interventions such as masking or school closures are necessary.
At best, wastewater monitoring may pick up a new virus when it first arrives in a new area; Early closures in a very localized area could prevent a future pandemic. Interestingly, researchers detected SARS-CoV-2 in archived wastewater samples collected before anyone was diagnosed with COVID-19. If wastewater monitoring were part of the public health infrastructure established in late 2019, it could have provided an early warning that SARS-CoV-2 had become a global threat.
Currently, though, establishing and operating a national wastewater monitoring system, particularly one that includes building-level monitoring at key sites, is still very expensive and labour-intensive.
Ongoing research and development efforts are trying to simplify and automate wastewater sampling. On the analysis side, adapting PCR and sequencing techniques to detect other pathogens, including new ones, will be vital to take full advantage of such a system. Ultimately, wastewater monitoring can help support a future in which epidemics are less deadly and have less social and economic impact.
CDC turns to wastewater data to track the spread of COVID
Introduction of the conversation
This article has been republished from The Conversation under a Creative Commons license. Read the original article.
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