The study, which was completed in conjunction with the national airline Qantas and the University of Queensland, found wastewater testing can be effective to screen for passengers for COVID-19 at points of entry.
Warish Ahmed, the lead author of the CSIRO’s study, said in a statement released Oct. 18, said that the wastewater samples will enable authorities to cover any lag times in detecting the virus from PCR tests which can take longer.
“It provides an extra layer of data if there is a possible lag in viral detection in deep nasal and throat samples and if passengers are yet to show symptoms,” Ahmed said.
Professor Jochen Muller from the University of Queensland’s Alliance for Environmental Health Sciences and co-author on the research said wastewater testing could also be useful as an additional tool.
“The paper recommends that wastewater surveillance should be used as part of an efficient clinical surveillance and quarantine system—providing multiple lines of evidence of the COVID-19 infection status of passengers during international travel.”
Published today, Oct. 18, in Environment International, the study analysed wastewater samples from lavatories of 37 Australian Government repatriation flights from COVID-hotspots landing at Darwin International Airport between December 2020 and March of this year. This includes flights from India, France, UK, South Africa, Canada and Germany.
The study performed three tests on the wastewater samples, and overall, there was an accuracy of 83.7 percent for detecting COVID-19 cases. This is 8 to 21.5 percent better than a single test performed alone.
Infected people shed the virus in their faeces around 2-5 days before showing symptoms. Therefore, wastewater surveillance may potentially screen individuals that are still asymptomatic to prevent further infections.
Wastewater samples from 24 of the 37 —around 65 percent— were positive for the virus even though all of the passengers aged five and over tested negative to the virus two days before landing.
However, there are concerns over the accuracy of wastewater testing, given separate studies have shown that wastewater testing is not perfect and that rare individuals may not shed the virus through their faeces; instead, they may transmit the viral particles in respiratory droplets by sneezing and coughing.
It has also been reported that in the first week of illness, there are more viral particles in the upper respiratory tracts than anywhere else.
Furthermore, it is also possible that some of the children under five in this study may have shed the virus but were exempt from the pre-departure clinical testing. Additionally, there may still be shedding in the faeces for five to seven weeks after infection; including those that have recovered and no longer infectious.
The passengers from the study were quarantined for 14 days after arriving, and clinical testing found 1.7 percent of passengers out of the 6570 to be positive for the virus.
Nevertheless, researchers speculate that surveillance of wastewater may also provide the possibility of screening for new COVID-19 variants of concern.