Wastewater testing can detect COVID-19 cases weeks before people show clinical signs

A new study from Australia’s national science agency, CSIRO, and the University of Queensland provides further evidence that wastewater (untreated sewage) testing can detect COVID-19 in communities weeks before people display symptoms, suggesting this testing could provide a targeted early detection system as economies re-open and people become more mobile.

Wastewater testing can detect COVID-19 cases weeks before people show clinical signs
Digital PCR used to quantify SARS-CoV 2 RNA in sewage or other environmental samples.

This retrospective study looked back at wastewater samples that had been collected in February and early March 2020, in Brisbane, Australia, which were preserved for later analysis.

When analysed for this study, researchers found the archived samples were able to detect the genetic fingerprint of the virus up to three weeks before the first COVID-19 cases were publicly reported through the limited clinical testing available at the time.

Researchers believe this could allow public health professionals to target specific areas for public health interventions and avoid a full lock-down of larger regions.

CSIRO Chief Executive Dr Larry Marshall said wastewater testing is one of the critical science-driven tools that can help open up borders to drive Australia’s recovery and reduce future disruption.

Australians want to do the right thing, but this solution from science detects the disease before people feel the symptoms, so we can outthink and outmanoeuvre this insidious virus. It’s a true Team Australia approach when states can stay open by targeting their response to contain the disease, saving whole regions from have to shut down; and Team Australia is what we need to grow our way back to recovery.”

Dr Larry Marshall, Chief executive, CSIRO

Published in Science of the Total Environment, the study indicated that if sampling is both frequent and widespread enough, the testing can detect the virus before people feel sick, as their bodies start shedding fragments of the virus into the wastewater system through their faeces before they know they’re infected.

Director of CSIRO’s Australian Centre for Disease Preparedness, Professor Trevor Drew, confirmed that people can become infected and spread (or ‘shed’) SARS-CoV-2, the virus that causes COVID-19, before they may show any clinical signs.  

“Evidence has shown that this virus can infect people and replicate itself for some time before they start showing any symptoms, and some people are entirely asymptomatic but still shed the virus,” Professor Drew said.  

“Like many other coronaviruses, SARS-CoV-2 replicates in our digestive system, as well as in our lungs, so can be detected in effluent water a few days before enough people are clinically effected for us to detect the virus in people who are ill.”

The researchers have been assisting Queensland Health with their wastewater surveillance program since July 2020, testing sewage for traces of the COVID-19 virus in dozens of locations across Queensland to enhance their response to the pandemic, sharing the results online.

CSIRO lead author Dr Warish Ahmed said wastewater testing is gaining international recognition as an important tool in the pandemic response.

The initial detections in archived samples, which occurred while there were limited clinical reported cases at the time because of lack of kits, demonstrate the potential of wastewater-based testing as an early warning system for the community. When integrated into disease surveillance and monitoring systems, wastewater monitoring may assist management efforts to identify hotspots and target localized public health responses, such as increased individual testing, setting up fever clinics, and the provision of health warnings.”

Dr Warish Ahmed, Lead author, CSIRO

The analysis involves tracking genetic fragments of the COVID-19 virus which are flushed into the wastewater system through infected people’s feces.

The study showed the virus was detected in samples taken from a Brisbane South wastewater treatment plant in late February 2020, up to three weeks before the first clinical case was reported.  

Only two other studies have been published globally confirming the virus detection between one and four weeks prior to people showing clinical symptoms.

CSIRO and UQ are also continuing to improve their testing methods to achieve more sensitive detection of the COVID-19 virus in wastewater testing and to reduce uncertainty in the way wastewater samples are collected.  

This includes a paper, published in Environmental Research , showing that testing 24-hour composite wastewater samples may increase analytical sensitivity and decrease variability compared to samples taken at a point in time.  

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