Wastewater monitoring gained momentum during the COVID-19 pandemic – and here’s how it can help stave off future outbreaks
Wastewater monitoring gained momentum during the COVID-19 pandemic – and here’s how it can help stave off future outbreaks

Wastewater monitoring gained momentum during the COVID-19 pandemic – and here’s how it can help stave off future outbreaks

Where does the data come from?

During the pandemic, the US developed Centers for Disease Control and Prevention National wastewater monitoring system specifically to track SARS-CoV-2 across the country. Over 800 sites report data to this NWSS system, but not all states and counties are currently represented.

Many government agencies, such as Colorado Department of Public Health and Environmentand cities, which Tempe, Arizona, have their own data reporting dashboards. Some companies that perform wastewater analysis report data on their own dashboardsalso.

In our opinion, the NWSS represents an exciting first step in monitoring the health of the population through wastewater. Similar systems are being established in other countries, including Australia and New Zealand.

What does wastewater data actually 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 living in the sewer, so it is anonymous, impartial and fair. More importantly, it is also impossible to trace the infection back to a particular person, household or neighborhood without taking additional samples.

Wastewater monitoring is not dependent on the availability of clinical trials or individuals reporting their test results. It also detects asymptomatic and presymptomatic cases of COVID-19; this is critical because people who are infected but not feeling sick can still spread COVID-19.

In our opinion, wastewater testing is becoming increasingly important as more COVID-19 tests are performed at home. And because vaccination has also led to milder and asymptomatic cases of COVID-19, people can become infected without being tested at all. These factors mean that data from clinical cases are less informative than earlier in the pandemic, while wastewater data remain a consistent indicator of the level of infection in the local community.

So far, you can not accurately predict the number of infected individuals in a community based on the level of virus in its wastewater. The stage of a person’s infection, how their body reacts to the virus, the viral variant, how far a person was from where the wastewater sample was taken, even the weather can all affect the amount of SARS-CoV-2 measured in waste water.

But researchers can deduce relative changes in the infection rate. Watching viral levels go up and down in sewage gives a glimpse of whether cases are rising or falling in society as a whole.

Because SARS-CoV-2 can be detected in sewage days or even weeks before outbreaks occur, sewage monitoring can provide an early warning that public health measures may be warranted. And trends in the signal are important – if you know the levels are rising, it may be a good time to reintroduce a mask mandate or recommend working from home. At present, public health officials use wastewater monitoring data along with other information as test positivity rates and the number of clinical cases and admissions to the community to make these kinds of decisions.

Sequencing data can also help detect new variants and monitor their levels, allowing health responses to take into account the characteristics of the variant present.

In smaller populations, such as in dormitories and nursing homes, wastewater monitoring can detect a small number of infected people. It may sound alarming that targeted clinical testing is to identify infected people for isolation. Early detection, targeted testing and quarantine are effective in preventing outbreaks. Instead of using clinical trials for routine monitoring, administrators may reserve disruptive clinical trials for times when SARS-CoV-2 is detected in wastewater.

What will surveillance look like in the future?

Widespread and routine use of wastewater monitoring would provide public health authorities with access to information on the level of a range of potential infections in American communities. These data can guide decisions on where to make additional resources available to communities, such as holding test or vaccination clinics in places where the infection is on the rise. It can also help determine when interventions such as masking or school closures are necessary.

At best, wastewater monitoring can catch a new virus once it arrives in a new area; an early shutdown in the very local area could potentially prevent a future pandemic. Interestingly, researchers have discovered SARS-CoV-2 in archived wastewater samples collected before someone had been diagnosed with COVID-19. If wastewater monitoring had been part of the established public health infrastructure back in late 2019, it could have given an earlier warning that SARS-CoV-2 was becoming a global threat.

So far, the establishment and operation of a national wastewater monitoring system, especially one that includes building-level monitoring at key sites, is still too expensive and labor-intensive.

Ongoing research and development efforts seek to simplify and automate wastewater sampling. On the assay side, adapting PCR and sequencing technologies to detect other pathogens, including new ones, will be crucial to take full advantage of such a system. Ultimately, wastewater monitoring can help support a future where pandemics are far less deadly and have less social and economic consequences.

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