The flush of the toilet, the swirl in the shower drain, the suds down the sink. We don’t give our wastewater much thought, but it can provide one of the earliest warnings that COVID-19 is in our midst.
Sewage holds a treasure trove of viral data and we’re using it to help fight the pandemic.
The NSW Sewage Surveillance Research Program tests untreated sewage for fragments of the COVID-19 (SARS-CoV-2) virus and provides the data to support NSW Health’s response.
The ColoSSoS project is led by Water Research Australia and is a collaboration of experts from many disciplines and states, including Sydney Water.
The national program’s research could inform policies on disease control measures, such as limits on gatherings and travel, and could help target pandemic control efforts and investments.
Within the chosen sewage catchment areas, researchers collect samples of wastewater at the inlet of the treatment plant, before it goes through the treatment process.
The samples are then analysed with a specialised test that looks for fragments of the virus (not the whole virus, so it’s not necessarily infectious when detected).
Dr Katrina Wall, Acting Manager of the Water Unit for Health Protection NSW said, ‘It’s not a new thing to look for viruses in wastewater, but this virus is new, so the methods had to be developed for accuracy specific to this virus’.
And it’s not a test every lab can do.
Dr Zenah Bradford-Hartke, Policy Analyst for the Water Unit said, ‘The labs that can run the test have years of experience in analysing viruses from wastewater. We don’t have extensive lab capacity for this testing.’
The locations for sampling must be prioritised, a discussion which is guided by the Chief Health Officer and an expert steering committee. They identify locations of concern by considering risk factors, tourism, borders and other issues which may affect how the virus is travelling throughout the state.
A positive sample in sewage can prompt action.
‘Some research from other jurisdictions and internationally has picked up a virus signal prior to knowing about clinical cases in the area. It can be like an early warning system,’ said Dr Bradford-Hartke.
In NSW, the research results have been helpful in driving increased testing and reminding people to be vigilant.
‘I think it has shown how sensitive this test can be, to find virus fragments in a small or mid-size community when there are only one or two clinical cases,’ said Dr Wall. ‘It definitely helped to drive up testing in the ski fields. When it was found in the sewage there, they didn’t know of any clinical cases in the area.’
Dr Wall said, ‘COVID-19 isn’t a very hardy virus and sewage treatment processes are very successful at inactivating it, so there’s little risk to the public on the other side of the treatment process.
‘For wastewater workers, they are watchful for hardy pathogens and COVID-19 doesn’t require any additional work-safety measures.’
Normal (treated, tap) drinking water is safe, especially as it undergoes extensive treatment.
Despite a remarkably sensitive test that can detect mere fragments of virus in large catchment areas, resarches are still learning about COVID-19 in sewage.
Dr Wall said, ‘We’re still evaluating what finding the fragments means. What does the amount of viral shedding in sewage indicate about how much infection there is across the population? What can samples tell us about the movements of the population?’.
Researchers don’t yet fully understand how the distance could matter from where the sample is taken to where virus was shed. How far can virus fragments travel and still be detected? Should larger areas be tested in smaller segments, such as collecting samples at pump stations or sewer mains to narrow down where the signal is coming from?
Dr Bradford-Hartke said, ‘People can still shed the virus after they have recovered and are not infectious, so there is still validation work underway to know, when we pick up the signal, how that compares with active cases at the time.’
In wastewater treatment, pathogens are characterized by the typical load or concentration you would expect to see reflected in sewage so a treatment process can be designed to address it.
Researchers are still working to understand the expected load for COVID-19.
Dr Bradford-Hartke said, ‘If you understand that (load) and combine that with understanding of shedding, could you estimate the number of cases in that catchment population?
‘We need further understanding of how people shed COVID-19 to be able to create a model that estimates how many COVID-19 cases are in a catchment based on load.’
COVID-19 sewage surveillance won’t stop anytime soon.
Dr Bradford-Hartke said, ‘There is particular interest in using sewage surveillance in areas where access to clinical testing isn’t as good. In those areas, it can be a helpful addition in formulating a public health response.’
Dr Wall said, ‘We’ll be living with this virus for quite some time, so the early warning aspect of it is quite useful. It helps us keep a close eye on it and can give us a signal before we’ve detected clinical symptoms or cases in the community. It’s an adjunct to everything else we do to keep people safe.’
The researchers are providing a report to the PHEOC team every week. Where a test result does trigger a response, you can find out about it in the COVID-19 weekly surveillance reports.
