Testing sewage from airliner toilets for traces of coronavirus could offer New Zealand an extra layer of protection against Covid-19, a public health expert says. Photo / Brett Phibbs
Testing sewage from airliner toilets for traces of coronavirus could offer New Zealand an extra layer of protection against Covid-19, a public health expert says. Photo / Brett Phibbs
Testing sewage from airliner toilets for traces of coronavirus could offer New Zealand an extra layer of protection against Covid-19, a public health expert says.
In theweeks after the outbreak of Auckland's Valentine's Day cluster, it gave authorities some reassurance that confirmed community cases weren't the tip of a Covid-19 iceberg.
The approach is also used in a range of ways overseas - and in the United Arab Emirates (UAE), sewage samples have been collected from commercial airliners.
In a recent UAE study that involved collecting nearly 200 samples from aircraft, researchers suggested that if the virus was being detected in high amounts amid air travel from certain countries, governments could use the data to suspend flight paths.
University of Otago epidemiologist Professor Nick Wilson said this could be a strategy for New Zealand to also explore, other than on flights from Australia.
"This approach could be trialled on incoming flights containing travellers from red-zone countries where there might be particular issues with the quality of pre-flight testing," he said, adding this seemed to have been a concern with flights from India.
A positive test from aircraft sewage on an incoming flight could prompt the need for "heightened awareness" among aircrew for symptoms, as well as full compliance with daily saliva testing.
For passengers transiting into managed isolation and quarantine (MIQ), it could prove another tool to detect cases early, he said, and move affected travellers to appropriate facilities.
A Ministry of Health spokesperson said the ministry kept a constant watch on evidence and science to ensure New Zealand had the "best possible settings".
But they said wastewater testing of flights currently wouldn't give officials "any additional information".
That was because the current regime already required PCR tests from travellers on red zone flights on their first and third days here.
"Additionally, depending on the duration of the flight, people may or may not use the toilets on board."
ESR Science Leader Dr Brent Gilpin said the institute had also looked into testing of wastewater from flights.
"But at this stage, while we are isolating and testing most arrivals, it doesn't add significant value to the current surveillance system," he said.
"Aside from the obvious - not everyone deposits faeces on a flight, if it were to be employed, there are quite a few operational issues to overcome including cleaning procedures of the tanks between flights, sampling, speed of analysis, response and other issues like shedding in the post infectious phase."
Wilson nonetheless felt the approach would have real value to New Zealand in future, when other control measures were being wound down.
Covid-19 modeller Professor Michael Plank, of Te Punaha Matatini, agreed there was potential for the method later.
"Looking ahead, this approach could also be useful if border restrictions are relaxed for other relatively low-risk countries in the future," he said.
"The Government collects contact details of all incoming passengers so if there was a positive sewage result on a green-zone flight they could contact everyone on that flight and ask them to get tested."
Sampling of city wastewater plants for traces of the virus has been carried out in New Zealand since last April. Photo / ESR
Wilson's fellow Otago epidemiologists, Professor Michael Baker and Dr Amanda Kvalsvig, were similarly interested in the concept.
"I think it is important to distinguish countries which have eliminated Covid-19 from those where transmission is widespread, as the role of such testing will be very different in these diverse settings," Baker said.
"On that basis, New Zealand could look to Australia in particular for examples of best practice, particularly as a backup system for early case and outbreak detection."
Kvalsvig saw potential for screening for other pathogens coming into New Zealand via air travel.
"You could imagine a permanent system where wastewater from incoming aircraft is routinely monitored for an array of microbes of public health interest, as a very useful component of New Zealand's biosecurity surveillance," she said.
"It could work well as an early warning system for influenza virus, for example, identifying new influenza variants arriving from the Northern Hemisphere winter season or even an emerging pandemic."
The ministry spokesperson said wastewater testing - which detects the presence of SARS-CoV-2 RNA shed in faeces by infectious persons - could be used as an "early warning system" for outbreaks, as well as a way to indicate an increase or decrease in case numbers.
In a recent pilot study, ESR recently rolled out wastewater testing across centres with MIQ facilities, such as East Auckland, Christchurch, Hamilton, Rotorua and Wellington.
It also targeted some other cities and suburbs, including West Auckland and Rosedale, Dunedin, Gisborne, Invercargill, Napier, central and north Nelson, New Plymouth, Palmerston North, Queenstown, Taupō and Whangārei.
The ministry was now reviewing the results of the work.
"However, SARS-CoV-2 RNA can also be shed for a number of weeks following recovery," the spokesperson said.
"We have seen this with wastewater testing to date in New Zealand where virus RNA fragments were detected in wastewater samples collected at a location near the homes of people who had recently recovered from Covid-19."
