A unique study led by the Institute of Environmental Science and Research (ESR) with Watercare and the University of Auckland confirms the benefit of wastewater testing as an early warning system for COVID-19.
The paper: Sensitivity of wastewater-based epidemiology for detection of SARS-CoV-2 RNA in a low prevalence setting, has been released as a preprint on medRxiv. This study assessed the sensitivity of community wastewater sampling to detect potentially infectious COVID-19 cases in a community.
Joanne Hewitt, Senior Scientist and project co-lead at ESR said the results of the four-month study demonstrated that the testing of wastewater was a reliable and sensitive platform for detecting COVID-19 infections in the community scale.
“Even when case prevalence is low, we saw that wastewater testing provided a good opportunity of early detection for community outbreaks of COVID-19, however with 10 or more cases the probability of detecting the virus moves to more than 87 percent.”
To assess the sensitivity of the method of surveillance, researchers conducted reviewed all symptomatic and asymptomatic cases, from July to November 2020, in a population of approximately 120,000 where cases were known and uniquely all located in a single managed isolation and quarantine facility (MIQF) building.
The study involved the daily collection of 113 composite wastewater samples from the sewer outside the MIQF and from the wastewater catchment located 5km downstream.
Hewitt says that over the period, SARS-CoV-2 RNA (that causes COVID-19) was detected in 54 percent of cases from the wastewater catchment, compared to 95 percent at the MIQF.
“Logistic regression, the process of modelling the probability of a discrete outcome given an input variable, was used to estimate the shedding of the virus into wastewater based on four infectious shedding models. With a total of 5 and 10 COVID-19 infectious cases per 100,000 population the predicated probability of detection at the treatment plant was estimated to be 28 percent and 41 percent, respectively, however when a more realistic proportional shedding model was used, this increased to 58 percent and 87 percent for 5 and 10 cases, respectively.
“In other words,” says Joanne Hewitt, “when 10 individuals were actively shedding the virus in a catchment of 100,000 individuals, there was a high likelihood of detecting viral RNA in wastewater. The evidence provided confidence that the detections at the treatment plant were associated with increasing COVID-19 cases.”
Sam Trowsdale, lead scientist from the University of Auckland says the research was pioneering work for the COVID-19 early warning surveillance system.
“We made use of the rather unique situation in NZ, where there was no one with COVID-19 in the community and a well quantified small-number of people with COVID-19 in managed isolation. Sampling wastewater from both locations meant we could establish techniques for the ultra-sensitive detection of SARS-CoV-2 in wastewater.”
Brett Cowan, ESR Chief Scientist says the results of the study reaffirmed the role of wastewater sampling as part of New Zealand’s response to COVID-19, along with community testing and genome sequencing.
“Wastewater-based epidemiology is being used as a critical part of international public health responses to COVID-19 to monitor infections at the community level. The results of the study highlight that if the virus is in the community, then there is a strong probability we will pick it up.
“What COVID-19 has highlighted is the need to get onto viruses as quickly as possible to minimise the spread. We are confident wastewater testing is going to become an even more important part of our public health efforts.”
Brent Gilpin, ESR Water and Waste Team Manager added that the findings of the study were being borne out by the detections uncovered in the recent outbreak.
“The recent example of detecting SARS-CoV-2 in Warkworth further demonstrates the benefit of the testing of wastewater samples. A positive detection in the wastewater triggered health officials to specifically advise people in the area to get tested if they had any COVID-19 symptoms, despite there being no known cases.
This research was supported by MBIE’s Covid-19 Innovation Acceleration Fund.