Experts Explain Why It’s Still Possible to Have COVID-19 Cases in Cruises

By now, you’ve probably heard about what happened to Royal Caribbean’s Quantum On The Seas.

A passenger tested positive for Covid-19 onboard the ship and the cruise was cut short.

And because of that single case, which subsequently tested negative, a scheduled cruise on 10 Dec 2020 was also cancelled.

Before the cruise-to-nowhere was approved by the Singapore government, countless precautions and protocols were put into place, including pre-departure Covid-19 tests, 50% capacity limit and the authorities even hired a risk assessment company to put into place a safety framework for these cruises.

So, why is it still possible to have a case (regardless of whether the latest incident is a false positive or not)?

Experts Explain Why It’s Still Possible to Have COVID-19 Cases in Cruises

The crux of the matter, according to experts ST spoke to, is that no Covid-19 testing regime is foolproof.

While a polymerase chain reaction (PCR) test is accurate, it’s not able to detect the Covid-19 virus in a person’s body during the incubation period.

The incubation period for Covid-19 is an average of five days.

This means that if the man had been infected with the coronavirus just prior to departure, the pre-departure Covid-19 test might not be able to detect its presence at all.

An Important Need To Investigate

It’s important now to establish a few things:

Has there been any transmission on board the ship? This means that more tests have to be done on the man as well as on the other passengers onboard.

Is it a false-positive case? In the late hours of 9 Dec, the Ministry of Health (MOH) announced that the 83-year-old Covid-19 patient tested negative twice for Covid-19 after his initial positive results.

One was a retest of his original sample while the other was taking a fresh sample from the man for testing.

It was added that the man will be tested again on 10 Dec 2020 to “verify his Covid-19 status”.

His close contacts on board the cruise ship have also tested negative for the coronavirus.

The third thing to establish is where he had got infected with the virus.

Professor Dale Fisher from NUH thinks that the man is unlikely to have contracted the coronavirus onboard the ship.

That’s in view of the short duration of the trip (he was on board the cruise ship for three days).

Professor Teo Yik Ying, dean of NUS’s Saw Swee Hock School of Public Health, agreed with his views.

Pointing out that the incubation period of the virus can last between five and fourteen days on average, a person who’s infected might not start testing positive until at least five days have passed.

Of course, there have been cases of two-day incubation periods so the possibility of the man being infected on board isn’t discounted.

Can You Still Go On Cruises?

While Professor Fisher still doesn’t support the idea of “cruise-to-nowhere”, he is confident that the current measures implemented can reduce the risk of a large outbreak.

Now is the time to assess how the measures hold up to a real-world situation.

“We’ll see how many other passengers need to be quarantined, and if any of those not quarantined develop infection. Soon we’ll see how effective the on-board measures are.” – Professor Dale Fisher

Next is to test the close contacts of the man after at least one infection cycle (2 weeks) to see if any transmission has occurred.

If there’s no spread, this means that the current system is effective enough.

This is also a reminder of why safe management measures and the use of TraceTogether are mandatory, Professor Teo added.

Low Risk Of Spillage

The experts also believe that cruises should not be banned immediately.

Stressing the need to assess the aftermath, Professor Teo asks for people in Singapore not to be alarmed as the risk of infections spilling to the local community is “low”.

In fact, there could be a silver lining in the situation.

Such cases are inevitable as Singapore gradually resumes normal activities, “particularly the nightlife sector”, but if the situation is contained despite the interaction, it means Singapore can go ahead to gradually resume more activities.

Disagreement

Not all experts agree, however.

Associate Professor Cook from NUS Saw Swee Hock School of Public Health wasn’t surprised that a case has surfaced.

He was more surprised that the problem cropped up so early.

PCR Vs Rapid Tests

As for whether PCR tests before departure are still necessary, given what’s happened, Professor Teo is of the opinion that they are still essential because, even with the window of possible infection, the PCR test is more accurate and sensitive.

As for rapid tests which can be done on the day of departure, it allows for no window of infection but is less sensitive and could let through a real Covid-19 case.

Featured Image: Igor Grochev / Shutterstock.com