Wastewater is one of the most important parts of the human ecosystem and a resource that can be used to detect disease and other pathogens that can be passed to humans through contact with water or food. A wastewater-based disease surveillance approach offers promising prospects for monitoring potential outbreaks in communities.
Wastewater monitoring has been used in the detection of viruses for a long time. The earliest record of wastewater being used for this purpose is from the 1950s. In 1952, Jonas Salk, who was later awarded a Nobel Prize in Medicine for his discovery of the polio vaccine, began researching how to use sewage as a source of biological material to test for various viruses. This research led him to discover that sewage contained viable cells that could be used to detect viral diseases.
These discoveries paved the way for further research into using wastewater as an indicator of disease. It was wastewater monitoring and analysis that played an important role in monitoring and detecting the amount of COVID-19 virus prevalent in communities throughout the pandemic.
Exactly What Does Wastewater Data Show?
In large populations, SARS-CoV-2 levels in wastewater can be used as a reliable indicator of infection levels. As the system monitors everyone who lives in the vicinity of a sewer system, information at an individual level is anonymous and additional samples and investigation would be necessary to trace the infection back to a specific individual, household or neighborhood.
Water surveillance does not rely on clinical tests or reporting of test results. It also detects asymptomatic and presymptomatic COVID-19 cases; this is important because people who are infected but don't feel sick can still spread it; in this respect, the extent of an outbreak can be suppressed with careful monitoring of data and precautionary action.
There is no reliable way to predict the number of infected people in a community from the virus level in its wastewater. A person's stage of infection, their body's response to the virus, the viral variant, how far away they were from where the wastewater sample was taken and even the weather can impact how much SARS-CoV-2 is measured in sewage. Having said that, the data can ascertain a ‘viral load’ which enables professionals to identify the amount of virus present as a proportion of the neighborhood and work out patterns.
As viral levels in sewage increase and decrease, scientists can make inferences about changes in infection rates. Since SARS-CoV-2 can be detected in wastewater days or even weeks before outbreaks, wastewater monitoring can provide early warnings that public health measures are warranted.
It is also important to pay attention to trends in the signal. For example, if levels are rising, the government can consider reintroducing a mask mandate or suggesting workers work from home. Currently, public health officials make these types of decisions using wastewater monitoring data and testing positivity rates and hospitalization rates in the community.
Using data from sequencing, health care providers can detect new variants and monitor their levels to tailor responses according to the variant's characteristics.
Challenges Surrounding Wastewater Monitoring
Water samples can pose a challenge when it comes to detecting viruses accurately. Before concentrating viruses by filtration, flocculation, precipitation, or centrifugation, larger quantities of sewage sludge are filtered to remove debris. There is a possibility of damage to genomic material through concentration techniques and substances can build up, which inhibit molecular analysis. In addition to microbes and viruses, sewage also contains human DNA, which may cause false positives or misinterpretation of results.
Also, some experts caution that the data collected from these studies could also pose privacy concerns, especially since samples are often obtained from public sources without consent.
At the University of Alberta, professor emeritus of laboratory medicine and pathology Steve Hrudey said that bioethics has historically been based upon the principle of non-harm and the idea of informed consent. However, it is impossible to get informed consent using this technique.
Besides this, in the short term at least, establishing and operating a national wastewater surveillance system is still too expensive and labor-intensive, particularly one that includes building-level monitoring. These kinds of monitoring systems are currently not available to all communities, namely those that utilize septic systems and commercial buildings that have their own wastewater treatment systems and in this sense testing systems are still inequitable and cannot be implemented easily on a national scale.
The Best Use Cases for Wastewater Monitoring
With wastewater surveillance, it is feasible to test 100,000 people with just a wastewater sample rather than test thousands at random to identify if they are infected with a specific pathogen or even one that is just circulating. As was found with COVID-19, it was near enough impossible to test an entire population and using wastewater surveillance techniques could safeguard finite human and financial resources.
So, public health officials could gain insight into a range of potential infections by monitoring wastewater on a routine basis. In places where infections are on the rise, this data could help determine where additional resources should be provided, such as holding testing clinics or vaccination clinics. Additionally, it may help determine when school or senior residence closures, or masking are necessary.
The best scenario is that wastewater monitoring might detect a new virus when it first arrives in a new area; if an early shutdown can be achieved in this region, a potential pandemic can be averted. The SARS-CoV-2 virus was detected in archived wastewater samples collected before COVID-19 had first been recognized. Water monitoring could have provided an earlier warning of SARS-CoV-2's global threat if it had been included in the established public health infrastructure in late 2019.
Currently, most wastewater surveillance efforts focus on SARS-CoV-2, but the same techniques also work with polio viruses, influenza viruses and noroviruses. Drugs can also be detected in wastewater to provide insight into the level and type of drug use in a population.
What’s the Future for Wastewater Monitoring?
The implications of wastewater monitoring as a tool for outbreak detection and suppression are huge. However, there is still much work to be done in making this system more seamless, and public - private bodies need to be open to working together. Researchers are working on simplifying and automating wastewater sampling as part of ongoing research and development. To utilize such a system fully, it will be necessary to adapt PCR and sequencing technologies to detect other pathogens, including any new ones that come to fruition as a result of warmer weather and climate change.
However, public buy-in is probably the biggest factor standing in the way of wastewater monitoring as a tool for outbreak mitigation. If wastewater monitoring can be shown to be effective in reducing outbreaks, it will be easier to gain public support for implementing it across a national system - but that only happens if it's been shown to work first and doesn’t compromise individual privacy rights.
For commercial real estate developers and investors in Canada, employing wastewater surveillance procedures whether as an offsite or onsite service could become a value-add in long-term care settings, educational, multifamily and other medical buildings as a way to detect potential health threats to communities before they’re known by the authorities. With the arrival of new health threats now such as the Monkeypox virus, who knows whether wastewater monitoring in public and commercial buildings will be a ‘nice-to-have’ or it will become the new norm, whether that be forced or adopted.
In the long run, wastewater surveillance could certainly support a world in which pandemics are less deadly and have far less economic and social impact.
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