The Food & Health Bureau today said it is not unusual in the field of molecular biological testing that virus test results may not be consistently reproducible when a patient is tested repeatedly.
It was responding to media reports about case number 9741 which was confirmed on January 20, and previously underwent COVID-19 testing and received a negative result.
The bureau, having engaged Prof Yuen Kwok-yung, a member of the Expert Advisory Panel and his team at the University of Hong Kong to conduct a review and analysis, announced the results yesterday.
The case number 9741 patient consulted a private doctor on January 13. He had developed symptoms at that time but did not undergo testing.
He went to the community testing centre at Henry G. Leong Yaumatei Community Centre on January 15 and the mobile specimen collection station on Canton Road on January 18 for virus tests. Both returned negative results.
The patient later felt unwell and was sent to hospital on January 18. After admission, the hospital took his nasopharyngeal aspirate and throat swab for testing and he was subsequently confirmed positive.
The analysis found that the patient had a low viral load (Ct value of 33) and the serum antibody test came back positive on January 20, indicating a low risk of spreading the virus.
The upper respiratory tract specimens previously collected from the patient at the community testing centre and mobile specimen collection station showed a viral reaction after re-examination, but the viral load was extremely low (Ct value 39), which exceeded the limit that the common nucleic acid tests can accurately and consistently detect as positive reactions.
Experts estimated that the patient only received sampling for testing many days after the onset of the disease, adding that it would be better if the patient in this case had been tested at the first medical consultation.
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