Wastewater flushes out Covid-19 cases weeks before people show symptoms

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.

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,” Dr Marshall said.

“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.”

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,”  Dr Ahmed  said.

“When integrated into disease surveillance and monitoring systems, wastewater monitoring may assist management efforts to identify hotspots and target localised public health responses, such as increased individual testing, setting up fever clinics,  and the provision of health warnings.”

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

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.

Find out more about how the testing is done here (link to backgrounder with infographic).

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