A coronavirus case has forced the cruise ship Quantum of the Seas to return to the Marina Bay Cruise Center in Singapore. All 1,680 guests on board the vessel had cleared a mandatory Covid-19 test before the four-day cruise began. But after departure, an 83-year-old man, who had reported to the ship’s medical centre with a case of diarrhoea, tested positive for the virus. The passengers were confined to their cabins for more than 16 hours before they were allowed to disembark on December 9,…