A lab technician prepares to process wastewater samples for SARS-CoV-2 detection at Colorado State University. John Eisele/Colorado State University

Characterizing the nucleic acid sequence in more detail can provide information about viral strains – for instance, it can identify variants^[5] like omicron BA.2.

Currently, the vast majority of wastewater surveillance efforts are focused on SARS-CoV-2, but the same techniques work with other pathogens, including poliovirus^[6], influenza^[7] and noroviruses^[8].

Before the pandemic, one application was monitoring for rare poliovirus outbreaks^[9] in areas where polio vaccination is ongoing. Wastewater can also be monitored for signs of various drugs to give insights into the level and type of drug use in a population^[10].

Where does the data go?

During the pandemic, the U.S. Centers for Disease Control and Prevention developed the National Wastewater Surveillance System^[11] specifically to track SARS-CoV-2 across the country. Over 800 sites report data^[12] to this NWSS system, but not all states and counties are currently represented.

More than 800 sites that cover populations of various sizes report COVID-19 wastewater numbers to the CDC. CDC COVID Data Tracker, CC BY^[13][14]

Many state agencies, like the Colorado Department of Public Health and Environment^[15], and cities, like Tempe, Arizona^[16], have their own dashboards for reporting data. Some companies performing wastewater analysis report data on their own dashboards^[17], too.

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^[18] and New Zealand^[19].

What does wastewater data really show?

SARS-CoV-2 levels in wastewater from large populations are an excellent indicator of the infection level in a community. The system automatically monitors everyone who lives in the sewershed, so it’s anonymous, unbiased and equitable. Importantly, it is also impossible to track the infection back to a particular person, household or neighborhood without taking additional samples.

Wastewater surveillance doesn’t rely on the availability of clinical tests or people reporting their test results. It also picks up asymptomatic and pre-symptomatic cases of COVID-19; this is critical because people who are infected but don’t feel sick can still spread COVID-19^[20].

In our opinion, wastewater testing is increasingly important as more COVID-19 tests are done at home. And because vaccination has also led to more mild and asymptomatic cases of COVID-19^[21], people may be infected without getting tested at all. These factors mean that clinical case data are less informative than earlier in the pandemic, while wastewater data remains a consistent indicator of community infection level.

Wastewater surveillance doesn’t rely on people reporting a positive home test or even being aware of their infections. Spencer Platt/Getty Images News^[22]

So far, you can’t accurately predict the number of infected individuals in a community based on the level of virus in its wastewater. The stage of someone’s infection, how their body responds 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 amounts of SARS-CoV-2 measured in sewage^[23].

But scientists can infer relative changes in infection rates. Watching viral levels go up and down in sewage provides a glimpse of whether cases are rising or falling in the community as a whole.

Because SARS-CoV-2 can be detected in wastewater days or even weeks before outbreaks occur, wastewater monitoring can provide an early warning that public health measures may be warranted. And trends in the signal are important – if you know levels are rising^[24], it may be a good time to reinstitute a mask mandate or recommend working from home. At present, public health officials use wastewater monitoring data along with other information^[25] like test positivity rates and the number of clinical cases and hospitalizations in the community to make these kinds of decisions.

Data from sequencing 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 college dormitories and nursing homes, wastewater monitoring can detect a small number of infected people. That can sound the alarm that targeted clinical testing is in order to identify infected people for isolation. Early detection, targeted testing and quarantining are effective at preventing outbreaks^[26]. Rather than using clinical testing for routine monitoring, administrators can reserve disruptive clinical tests for times when SARS-CoV-2 is detected in the wastewater.

What will monitoring look like in the future?

Widespread and routine use of wastewater monitoring would give public health officials access to information about the levels of a range of potential infections in U.S. communities. This data could guide decisions about where to provide additional resources to communities, like holding testing or vaccination clinics in places where infection is on the rise. It could also help determine when interventions like masking or school closures are necessary.

In the best case, wastewater monitoring might catch a new virus when it first arrives in a new area; an early shutdown in the very localized area could potentially prevent a future pandemic. Interestingly, researchers have detected SARS-CoV-2 in archived wastewater samples collected before^[27] anyone 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 provided an earlier warning that SARS-CoV-2 was becoming a global threat.

For now, though, establishing and operating a national wastewater surveillance system, particularly one that includes building-level monitoring at key locations, is still too costly and labor-intensive.

Ongoing research and development efforts are trying to simplify and automate wastewater sampling. On the analysis side, adaptation of PCR and sequencing technologies to detect other pathogens, including novel ones, will be vital to take full advantage of such a system. Ultimately, wastewater surveillance could help support a future in which pandemics are far less deadly and have less social and economic impact.

[Research into coronavirus and other news from science Subscribe to The Conversation’s new science newsletter^[28].]

Authors: Susan De Long, Associate Professor of Civil and Environmental Engineering, Colorado State University

Read more https://theconversation.com/wastewater-monitoring-took-off-during-the-covid-19-pandemic-and-heres-how-it-could-help-head-off-future-outbreaks-180775