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Important to learn how to cope when testing errors occur: Experts

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While the news of the 83-year-old Royal Caribbean ship passenger eventually testing negative for Covid-19 is good, the incident has nevertheless cast the spotlight on Covid-19 testing and its accuracy.

Experts tell The Straits Times the same test sample can yield different results, due to the varying sensitivity and specificity of each type of Covid-19 test.

The Ministry of Health said yesterday it will support the laboratory on board the cruise ship "in its review of its testing processes".

Mr Michael Goh, head of international sales at Genting Cruise Lines and president of Dream Cruises, said last month that its safety regime includes a new real-time polymerase chain reaction (PCR) machine on board that yields Covid-19 test results in 60 minutes.

Royal Caribbean also has something similar on board.

While both liners did not reveal the accuracy of the testing machines on their ships, Mr Goh said yesterday that the PCR machine on Genting's World Dream was approved by the Health Sciences Authority, and PCR tests "remain the most accurate test available today".

Speaking to ST, infectious diseases specialist Leong Hoe Nam said the accuracy and precision of the machines on cruise ships are likely to be lower than that of the Health Ministry's laboratories, but are still useful within the scope of what they can do.

With no test able to be completely accurate, experts said it is important to learn how to cope when errors occur.

Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health, said: "The reality is that, as testing becomes more prevalent, erroneous results will emerge.

"These will have knock-on effects on whether a traveller is incorrectly denied entry or participation, or whether someone who is genuinely infected is missed and ends up seeding additional cases in the community.

"For observed positive findings, especially when diagnosed with rapid or point-of-care tests, it may be worth undergoing a round of retesting, preferably with an independent testing protocol to avoid any systematic errors.

"This way, we avoid the false scares that can happen, such as what happened on the Royal Caribbean ship."

Dr Leong said retesting capabilities may not be present on board ships, as they are usually done with lab experts in consultation with infectious disease experts.

As a result, he said the captain's decision to turn back on Wednesday morning was a prudent one.