The Centre for Health Protection said today it is investigating 11 additional COVID-19 cases, one of which is tentatively classified as a locally transmitted case with an unknown infection source involving the L452R mutant strain.
The case involves a 41-year-old woman who works as a part-time cleaner at Bridal Tea House Hotel, a designated quarantine hotel in Yau Ma Tei. She last went to work on July 1.
The centre's Communicable Disease Branch Head Dr Chuang Shuk-kwan said in a press briefing this afternoon that the patient preliminarily tested positive for the virus via the regular testing for hotel staff at a mobile specimen collection station on June 30.
However, she was tested twice after admission to hospital and the results were negative. She also tested negative for antibodies.
Dr Chuang added that the patient was assigned to clean the hotel rooms on June 30, and a COVID-19 imported case with the L452R mutant strain had stayed in one of them from June 20 to 27.
She said: "We found it a bit strange that the (COVID-19) patient tested positive and repeatedly negative with a negative serology (result).
"Of course, there may be an explanation such as she is at the very early stage after contracting the virus, so she is still incubating the virus. And after a few days, repeated testing may yield a positive result.
"But there may be other explanations. We wonder whether there is a possibility of, for example, environmental contamination.
"If the virus was not a live virus, she was not actually infected but carried the virus in her nasal passages, especially when she almost immediately took the swab (test) after she cleaned the room of a confirmed patient in Bridal Tea House Hotel. The virus she contracted may not be a live virus, but these are all postulations and possibilities that I cannot prove now.
"That is why we need some site visits and other investigations by Prof Yuen (Kwok-yung) and other colleagues to see whether there are any possibilities to explain (the case). Of course, we may need some time to observe the development."
The 10 imported cases arrived from the UK, Indonesia and Russia, of which nine carried the L452R mutant strain.
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