Testing Cruise Ship Sewage for Coronavirus Could Prevent Spread, Scientists Say

Testing sewage from vessels like planes and cruise ships for traces of the coronavirus that causes COVID-19 could help to prevent the disease spreading, according to a study.

SARS-CoV-2, the coronavirus that causes COVID-19, is known to lurk in the feces of infected people, and has been detected in wastewater in a number of past studies.

For the study published in the Journal of Travel Medicine, scientists took a total of five samples of sewage from a cruise ship and aircraft. They took 21 samples and tested them for SARS-CoV-2.

Two of the five samples were taken from a cruise ship on 23 April, 2020. Unconfirmed reports suggested 24 people with COVID-19 were onboard in the days before the samples were taken, the team wrote. Researchers also examined wastewater from aircraft that had flown from Los Angeles and Hong Kong to Brisbane, and New Delhi to Sydney in April and May 2020.

SARS-CoV-2 was found more often in the cruise ship samples, perhaps because more of these passengers had COVID-19, the team said.

The team discovered traces of SARS-CoV-2's genetic material in the wastewater samples from the first aircraft, but they were not found consistently in all of them. They didn't find SARS-CoV-2 in the samples from the other aircraft, mirroring passengers' test results.

There may be several explanations for the results from the first aircraft, the team said, including that concentrations of the virus may have been low and the tests used may not have been sensitive enough.

Despite finding the virus' genetic material in the aircraft's wastewater, passengers were not found to be infected. This may have been because traces of the virus were left behind from other flights, or the individual may not have developed symptoms and tested positive despite carrying it in their feces.

The differences between the aircraft and cruise ship samples may come down to the length of time passengers spend on each type of vessel, with people less likely to relieve themselves on aircraft, they said.

Lockdowns have affected economies around the world, and travel industries have been particularly hit. As economies reopen, air and cruise line passengers could play a significant role in importing new COVID-19 cases.

Testing wastewater from transport vessels, like planes and cruise ships, that have their own sanitation systems could help with testing and tracing efforts. But the team said sampling methods and tests should be optimized to make sure they are sensitive enough to detect SARS-CoV-2. Tests on wastewater and passengers could complement one another and help to avoid false negatives, they said.

Future studies could investigate whether it would be useful to take saliva or feces samples from passengers before they board a flight, with results released by the time they reach their destination, according to the scientists.

Co-author professor Jochen Mueller of Australia's University of Queensland's Queensland Alliance for Environmental Health Sciences said in a statement that testing vessel wastewater "could provide additional peace of mind to track and manage infection and play an important role in opening up long-haul flights or cruises resuming."

Noel McCarthy, professor of evidence in communicable disease epidemiology and control at Warwick Medical School who did not work on the paper, told Newsweek via email the study shows that "sampling wastewater from small and transient populations is difficult—in contrast to the ease and success with sewage sludge generated by large populations which seems to represent infection levels very well."

McCarthy said the study had "substantial limitations" and that it was unclear why the team sampled plans. "Many people may not defecate during a flight. The sample is therefore poorly representative and a negative [result] offers very little reassurance that there are not positive passengers."

It is also not useful to detect a sick person who has the virus in their faces but is no longer shedding the germ from their throat, he said.

Zhugen Yang, a lecturer at the Cranfield University Cranfield Water Science Institute who did not work on the paper, told Newsweek the current method for testing sewage for the coronavirus takes at least several hours or even days, and is not quick enough to enable authorities to test everyone on a plane where wastewater had tested positive to prevent them from leaving and spreading the virus.

But the approach described in the study is more cost-effective and less invasive than swabbing patients individually, he said.

If rapid testing kits for sewage can be rolled out, "this will ultimately help the government propose appropriate preventive measures against the ongoing COVID-19 pandemic," said Yang.

This article has been updated with comment from Noel McCarthy, and Zhugen Yang