The NSW Sewage Surveillance Program tests sewage for fragments of SARS-CoV-2, the virus that causes COVID-19, at sewage treatment plants across NSW. Before the Omicron wave, the program provided a valuable early warning system to support the NSW COVID response, particularly in regional communities. Now that COVID is widespread in the community, the focus of the program has changed from early warning to monitoring of trends to supplement information gathered through PCR and Rapid Antigen Testing.
The program now samples 22 sites throughout NSW on a weekly basis. Four sewage treatment plant sites in Greater Sydney and up to 18 regional locations are monitored weekly as sentinel sites. These sites were selected for their population size, geographical spread, proximity to state borders and transport routes and for the presence of vulnerable communities. Sewage samples will also provide support the NSW Health Pathology variant research project.
Sewage surveillance trends by epidemiological week
Transcript: Sewage Surveillance Research Program
The NSW Sewage Surveillance Program tests untreated sewage for fragments of the COVID-19 (SARS-CoV-2) virus at sewage treatment plants across NSW. The program covered over 90% of the population at its peak to provide data to support NSW Health's COVID-19 response.
Testing sewage helps to provide an indication of infections in an area. Results can be used to estimate changes in disease prevalence within the community. These tests provided data to support NSW Health's COVID-19 response.
Fragments of the virus that causes COVID-19 (SARS-CoV-2) can enter the sewage through an infected person's faeces and when washed off hands and bodies via sinks and showers.
SARS-CoV-2 is just one of many viruses that may be present in sewage. This program detects viral fragments of SARS-CoV-2.
Many, but not all people with COVID-19 have detectable virus in their faeces. However, fragments of the COVID-19 virus can also enter the sewage when washed off hands and bodies via sinks and showers.
Testing raw sewage for fragments of SARS-CoV-2 is a specialised test and cannot be carried out by many laboratories. NSW Health is working closely with Sydney Water and other national partners to ensure testing is of a high standard. Sewage must be filtered and processed before the laboratory looks for genetic material (target sequences of SARS-CoV-2 RNA, or ribonucleic acid). This is done using a process called PCR (polymerase chain reaction).
It is not well understood how long SARS-CoV-2 survives in sewage. Virus survival depends on the conditions in the sewer, such as temperature, presence of other microorganisms, and the amount of organic matter. However, SARS-CoV-2 is easily inactivated (killed) by detergents which are also present in sewage. SARS-CoV-2 virus is not expected to remain infectious in sewage for a long period.
No. COVID vaccines don't contain live virus. The available vaccines for COVID-19 do not result in viral shedding and cannot be detected as viral fragments in sewage.
There are several different situations that could be occurring when fragments of the SARS-CoV-2 virus are found in the sewage. It could mean there has been one or more people who are infectious with COVID-19 in the catchment area. It could also mean that there has been one or more people in the catchment area who have recently recovered and are no longer infectious. People who are recently recovered from COVID-19 can sometimes continue to shed virus fragments into the sewerage system for several weeks even after they are no longer infectious. It could also mean that a person with COVID-19 might have visited the community and has since left the area.
NSW Health undertook research to find out how many people shedding SARS-CoV-2 in a catchment area will cause a positive sewage result. This will depend on the number of people who live or work in the catchment area. It will also depend on other factors such as reduction in virus shedding over the time that people have COVID-19, dilution of virus within sewage, the period of time over which the sewage sample is collected, and the presence of chemicals and microorganisms in the sewage that affects how well the testing can detect SARS-CoV-2 virus fragments. The outcomes were published in
Retrospective epidemiological analysis of SARS-CoV-2 wastewater surveillance and case notifications data – New South Wales, Australia, 2020.
The Sewage Surveillance Program is not designed to identify individuals and does not detect which household the virus fragments are coming from.
Sewage treatment facilities serve different sized sewer catchment areas and different sized populations depending on their location. In the Sydney metropolitan area, some facilities collect sewage from over a million people from hundreds of thousands of households, while facilities in regional areas can serve large geographical areas but fewer households.
Sewage treatment facilities at Bondi and Malabar serve the areas where Sydney's quarantine hotels were located. These catchments were part of NSW Health's COVID-19 sewage surveillance program.
NSW hospitals and other health facilities dispose of
clinical waste such as human tissue, bulk body fluids or blood, blood-stained materials or equipment and laboratory specimens or cultures according to the regulations in the NSW Protection of the Environment Operations Act 1997. Sewage from hospitals treating COVID-19 patients is managed through the regular sewage treatment system.
There could still be cases in the community if COVID-19 virus is not detected in sewage. Typically, sewage moves from houses to the sewage treatment plant in a matter of hours, so case/s need to be in the catchment around the time of sampling. It will also depend on other factors such as virus shedding by people (which varies individually and over the course of the infection), dilution of virus within sewage – such as during rain, the period of time over which the sewage sample is collected, and the presence of chemicals and microorganisms in the sewage that affects how well the testing can detect SARS-CoV-2 virus fragments.
No. SARS-CoV-2 sewage surveillance was part of an integrated surveillance program and control measures across NSW. Sewage surveillance does not replace clinical testing of individuals or other control measures. We used this information alongside individual testing results and other health data to inform the NSW Health response.
The NSW Sewage Surveillance Program was only looking for fragments of SARS-CoV-2 to support NSW Health's pandemic response.
Testing for fragments of the COVID-19 (SARS-CoV-2) virus in sewage is a specialised test and is not routinely available. Testing locations were decided based on areas of concern and direction from the NSW Chief Health Officer. As COVID becomes more prevalent in the community, sewage surveillance can no longer be used to identify the introduction of cases into previously unaffected communities
SARS-CoV-2 is easily inactivated (killed) by usual sewage treatment processes, including chlorine and ultraviolet (UV) disinfection. Sewage also contains detergents and other substances that inactivate (kill) SARS-CoV-2 before it reaches the sewage treatment plant. Sewage is treated before discharge to the environment using UV or chlorine disinfection and is regulated by the NSW Environment Protection Authority.
Exposure to all disease-causing microorganisms in sewage should be managed by 'business as usual' hygiene practices such as good handwashing and the use of appropriate personal protective equipment.
Yes. Drinking water is treated before being delivered to your tap and is safe to drink unless your council informs you otherwise. The treatment is designed to inactivate (kill) or remove even the toughest microorganisms, including viruses, bacteria and protozoa. SARS-CoV-2 is not a hardy virus. No additional or modified treatment is required beyond the current 'business as usual' drinking water treatment.