Government advisers say tests show a mutated Covid strain must have spread silently from a returnee from Dubai to a foreign domestic helper in Tung Chung, after researchers confirmed that both were carrying an identical variant first identified in South Africa.

Microbiologist Yuen Kwok-yung said his colleagues at the University of Hong Kong found that the viral samples from the two have an identical genomic sequence.

He told RTHK on Saturday that the finding proved that the variant strain, which may be more infectious, has already spread in the community, indicating that urgent action is needed to stop it.

He said the findings showed that either there was leakage in border control or quarantine measures, or that problems with sampling and testing procedures had led to false negative findings.

The expert called on the government to conduct antibody tests for those who recently left quarantine hotels.

He said this especially applied to those who stayed in the Ramada chain, which operates the hotel where the Dubai returnee spent quarantine, and another hotel in Sai Ying Pun where another Filipino helper was found to be carrying mutated strains of the coronavirus, along with the family in the next room.

He also called for random retesting of samples that had been negative, and field auditing for private laboratories.

The government earlier announced mandatory tests for the SAR’s 370,000 domestic helpers, given that two of them were linked to cases of the new strain.

But Yuen warned that mass testing of helpers cannot replace “painstaking” contact tracing work to find out how the transmission chain started.

Another expert advising the government, David Hui, said researchers from the Polytechnic University also arrived at the same genomic sequencing conclusion.

“It is quite likely that the Indian guy who completed the 21-day hotel quarantine and was released into the community on April 9 actually sparked off some silent transmission in the community,” said the respiratory medicine professor from the Chinese University, referring to the man who flew in from Dubai.

“He mainly infected his friends in Jordan and indirectly he probably infected the foreign domestic helper,” he explained.

But he said there was no need to panic or revise social distancing measures, saying that stepping up testing is the right move.

“We should actually continue to increase the testing of the relatively high risk groups and wait and see, actually you need to look at the epidemiology and the development before you make adjustments to the social distancing measures, there’s no need to make any knee jerk reaction.”