Management at the hotel - the Grand Hyatt Singapore - said they had cleaned extensively and were monitoring staff and guests for infection but did not know "how, where or when" conference attendees were infected. The lion dancers, who posted photos of the event on Facebook, said they were virus free.
"Everyone assumes it was a delegate but it could have been a cleaner, it could have been a waiter," said Paul Tambyah, an infectious diseases expert at National University Singapore. He added it was "very important" to find "patient zero" to establish other possible "chains of transmission".
But time may be running out.