How is sewage monitored

Wastewater surveillance works because many infectious agents are excreted in bodily fluids, before and during active infection. When these fluids enter sewage systems, they are transported to a central wastewater treatment facility for processing where they can be detected.

The utility of wastewater surveillance was first recognized during the s, when researchers at Yale University conducted several experiments to assess the efficacy of polio vaccination campaigns. They tested the sewage in Middletown, Conn.

Thirty-five years later, the sensitivity of wastewater surveillance to monitor polio virus vaccination programs was confirmed in an elegant study that came to be known as the Helsinki polio virus experiment. Scientists flushed a polio vaccine down a toilet 20 kilometres away from a wastewater treatment plant. The researchers then collected wastewater samples from the facility over four days, and showed they could still detect the vaccine after million litres of wastewater had passed through the system.

They concluded that one infected person shedding the polio virus could be detected in a community of 10, residents. Other research demonstrated that outbreaks could be predicted by monitoring wastewater. For example, in Israel in the s, infectious polio virus was detected in sewage nine days before doctors identified the first case.

This approach was later adapted to monitor the success of polio vaccine campaigns internationally. In this issue, Peccia et al. Departing from traditional methods of examining wastewater, they report a high-resolution dataset generated from sewage sludge rather than influent and apply statistical analysis to infer the lead time their data may provide over epidemiological indicators. Their results strengthen the evidence that wastewater monitoring could be a powerful tool in tracking the spread of COVID It is a cost-effective way to survey transmission dynamics of entire communities.

It avoids the biases of other epidemiological indicators 4. It collects data from people who lack access to healthcare. And if it were successful in revealing infection dynamics earlier than diagnostic testing, it could provide public-health officials with near-real-time information on disease prevalence Fig.

Observed and theoretical time lags between infection and detection of increasing SARS-CoV-2 transmission in wastewater and the health system. Wide application of wastewater surveillance began in the s with efforts to eradicate poliovirus 5. As large-scale vaccination reduced polio transmission, the conventional approach to monitoring polio — tracking cases of acute flaccid paralysis — proved incapable of preventing outbreaks. Because poliovirus infections often present with non-specific symptoms, and acute flaccid paralysis occurs in only one of cases, the virus is able to spread undetected in areas where it was thought to be eliminated.

Testing sewage for poliovirus RNA is four to five times more sensitive in detecting outbreaks than monitoring communities for an atypical increase in cases of acute flaccid paralysis and has allowed entire communities to be continuously monitored 6. When poliovirus was detected in wastewater, mop-up vaccination campaigns prevented new cases of paralysis 7. Unlike polio, which spreads mainly by the fecal—oral route, COVID is fueled by respiratory droplets.

Despite claims to the contrary 9 , the fecal—oral route is unlikely to be a major factor in the pandemic. Released SARS-CoV-2 viruses are rapidly inactivated in the gastrointestinal-tract fluid and appear to be excreted primarily in a non-infective state. Concentrations of viral RNA in feces vary from patient to patient and over the course of the illness, but the signal can be detected for up to several weeks After excretion in feces, the viruses are diluted first in toilet water and then in other municipal wastewater constituents, including graywater for example, from showers and washing machines and, in some cases, industrial wastewaters and storm waters.

The viruses and their RNA travel through complex sewage systems and can be exposed to different temperatures and chemicals. Viral RNA appears to be stable over the temperatures and time frames involved in travel through the sewage system and settlement in primary wastewater treatment It is not currently possible to directly convert concentrations of viral RNA in wastewater to disease prevalence in a community.

First, the biological variability in viral RNA excretion over time and between individuals creates problems in this estimate. This variability is then compounded by variability in the sewer systems across communities, particularly their size, configuration, and whether they include stormwater and industrial waste. However, longitudinal trends of SARS-CoV-2 RNA levels in wastewater can still be helpful in complementing traditional surveillance methods to understand trends in community transmission.

In contrast, Peccia et al. Compared to non-enveloped viruses, coronaviruses have an affinity for wastewater solids 12 ; therefore, sludge monitoring at the community scale may offer greater sensitivity and less sample variance compared with wastewater influent monitoring. Peccia et al. Despite the relatively large variance noise in the sludge data, the high-resolution daily samples allowed the authors to establish a trend line, which correlated with reported cases.

Weekly or even semiweekly sludge samples may not have been as informative. An intriguing finding of this study is that sludge RNA gave early warning of epidemiological trends only when delays in diagnostic test processing were taken into account Fig. Theoretically, we expect wastewater surveillance to lead diagnostic tests by perhaps a week given what we know about viral dynamics in individuals and fecal shedding.

Shedding may occur soon after infection, whereas an infected person identified through the health system must develop symptoms and seek treatment before receiving a diagnosis. The finding of Peccia et al. However, epidemiological data in the early days of the pandemic were fraught with limitations, including limits on testing capacity and changes in testing guidance over time.

Before we abandon the prospect of wastewater as an early-warning system, further research with more robust epidemiological data is needed to better assess its potential. Moreover, in communities where testing delays persist, the early-warning value of wastewater surveillance is already clear.

Another benefit of wastewater surveillance is that it lacks the biases of the traditional indicators used to understand where disease transmission is occurring, increasing, or decreasing.

In the early days of the pandemic, a key indicator was the cumulative number of diagnosed cases. Later, more attention was given to hospitalizations, deaths and, most recently, rates of test positivity and serologic data. These indicators, while useful, have biases 4. Rapid progress in the development of sewage monitoring for SARS-CoV-2 offers the potential to contribute to public health action, such as the early indication of secondary outbreaks.

Many research labs and commercial labs have now gathered valuable experience in the handling of sewage samples and analysis of the virus. However, there are still issues regarding how to apply the results to advise health authorities, the handling of samples and the analytical techniques. This webinar will advance our common understanding of how these surveillance results can be used, and harmonize approaches and methods towards a global use for wastewater surveillance of COVID