International borders will start opening soon. Our researchers have proven that testing aircraft wastewater is another line of defence in managing and containing COVID-19.

In the first-ever comprehensive study of its type, we gathered wastewater samples from repatriation flights while planes were still sitting on the tarmac. These samples contain the first indication that incoming passengers could be infected with SARS-CoV-2, the virus that causes COVID-19.

Published in Environment International, the research analysed wastewater samples from lavatories of 37 Australian Government repatriation flights from COVID-19 hotspots. Locations included India, France, UK, South Africa, Canada and Germany. All flights arrived at Darwin International Airport between December 2020 and March 2021.

Our research was conducted in collaboration with Qantas and The University of Queensland. The team found aircraft wastewater samples from 24 of the 37 flights (65 per cent) showed a positive signal for SARS-CoV-2. This was despite passengers (except children under five) testing negative to the virus 48 hours before boarding.

Aircraft wastewater. Image of man collecting wastewater from an aircraft.
Qantas developed a sampling trap for collecting wastewater samples from planes to avoid cross contamination between flights. Image: Qantas.

Early detection of aircraft wastewater is key

Infected people shed the virus in their faeces for two to five days before showing symptoms. Traces of the virus can also be detected in wastewater from previously infected individuals. These people can still be shedding the virus. But they are no longer infectious to others (although this is typically a weaker signal).

We tested the wastewater during 14 days of mandatory quarantine in Darwin after arriving in Australia. Clinical tests identified 112 cases of COVID-19 among the 6570 passengers (1.7 per cent).

We spoke with the lead author, our researcher Dr Warish Ahmed, about why he believes it’s important to screen incoming passengers for COVID-19 at points of entry.

1. What makes this wastewater study so important?

This is the first comprehensive study of wastewater from flights returning from high case-load COVID-19 destinations. It’s also the first time we have matched the aircraft wastewater surveillance data with the follow-up clinical testing of passengers. This was during the 14-day mandatory quarantine.

Wastewater analysis demonstrated 87.5 per cent accuracy. This is when compared with clinical testing of passengers in quarantine facilities. For this study Qantas also developed a specialised, but simple, sampling trap for collecting wastewater samples. This helped avoid cross contamination from flight to flight.

Aircraft wastewater. Dr Ahmed collects samples from a fridge.
Dr Warish Ahmed conducts wastewater testing, which finds the presence of SARS-CoV-2 in sewage and other wastewater.

2. Why test the wastewater directly off the plane?

This method enables us to collect samples at the point of entry into Australia. Results can come back within 24 hours. If it’s urgent, we can return results in four hours. This will indicate which planes were positive for SARS-CoV-2 genetic fragments at the same time as passengers are entering quarantine. The method is also non-intrusive. It doesn’t require samples to be provided by individuals.

The majority of passengers who used the lavatory can be screened using a single aggregated wastewater sample. There is also very little ‘flush water’ in a plane lavatory. Therefore, the signal is less diluted than in a large quarantine facility.

3. We can detect COVID-19 in arriving passengers, even before they show symptoms. How can this help us control infection from overseas travellers?

Infected people shed SARS-CoV-2 two to five days before they show symptoms. Therefore, wastewater analysis gives an early heads-up that someone on the arriving flight potentially has COVID-19. This information may be useful to public health agencies in prioritising clinical testing. It also provides an extra layer of data if there is a possible lag in viral detection in deep nasal and throat swab samples.

This paper recommends that wastewater surveillance be used as part of an efficient clinical surveillance and quarantine system. This provides multiple lines of evidence of the COVID-19 infection status of passengers during international travel.

4. Wastewater testing found virus fragments in 65 per cent of the flights, but only 1.7 per cent of the passengers had COVID-19. How did the wastewater testing help?

The research found 87.5 per cent positive agreement between wastewater detection and clinical testing. The wastewater detection may come from someone who previously had COVID-19.

Clinical testing actually identified those individuals who comprised the 1.7 per cent of the passengers. This percentage of 6570 people is not a small number, considering Delta is highly transmissible.

As we come out of this pandemic, positive detection from wastewater surveillance may continue to be a useful indicator for health authorities. They would use this information to decide which passengers need further clinical testing.

5. How does the aircraft wastewater testing work?

The SARS-CoV-2 virus is diluted in aircraft wastewater. Once the wastewater sample is collected, it is then concentrated to a small volume. The virus’ RNA, carrying the genetic information, is then extracted from a portion of the concentrated sample.

The wastewater samples are analysed for specific genetic fragments of SARS-CoV-2 using RT-qPCR analysis. This process is akin to a molecular copy machine, which makes many (millions to billions) copies of molecular gene fragments. These serve as a molecular fingerprint – in this case for SARS-CoV-2. We quantify how many genetic pieces are present in a wastewater sample.

6. What if a COVID-19 infected person does not defaecate in the lavatory?

The successful application of wastewater surveillance largely depends on the toilet usage of passengers. It’s likely to be applicable for long-haul flights (longer than seven hours). Most passengers will urinate in the lavatory on flights. Also, nasal secretions of SARS-CoV-2 RNA via sputum and cough may also enter the wastewater tank via the lavatory sink.

The SARS-CoV-2 virus has been detected in both faeces and and other body fluids. This increases the chance of the detection rates in wastewater samples.

We caught up with Warish last year and discussed his work in this area.

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