COVID-19 test trial explained

November 21, 2020

The Government has been monitoring the latest developments of COVID-19 testing techniques and will assess such techniques with reference to scientific studies around the world and in Hong Kong, practical experience and expert advice.


The Food & Health Bureau made the statement today in response to media reports on discordant results between different tests conducted under the trial run of a COVID-19 nucleic acid testing technique at the Hong Kong International Airport.


The bureau confirmed that there were 25 cases in the trial that produced varying discordant results from tests conducted by different organisations, using different testing techniques and with specimen collected using different methods.


From these cases, six cases' deep throat saliva specimens collected at the Department of Health (DH)'s Temporary Specimen Collection Centre at the airport tested negative, while the gargle specimens collected by the organisation participating in the trial returned positive, negative or indeterminate results using different tests.


The bureau emphasised that there are advantages and limitations to different testing techniques and specimen collection methods for COVID-19 tests.


It explained that it is not uncommon that different testing techniques or specimen collection methods would generate discordant results, which might be due to the sensitivity and specificity of the technique, the viral load in the specimens provided by a sampling method or laboratory technical issues.


As for sampling methods, deep throat saliva, nasopharyngeal swab, and combined nasal and throat swab are more commonly used in Hong Kong for specimen collection, and the three methods are similar in accuracy and sensitivity, and could all effectively identify COVID-19 cases.


The DH's Public Health Laboratory Services Branch has also been monitoring whether other specimen collection methods would be suitable, the statement said, noting that there is no single testing technique or specimen collection method that can ensure complete accuracy.


The bureau stressed that the airport trial aimed to compare different testing techniques or specimen collection methods with the current arrangements.


It added that the Government will analyse the trial data and review the suitability of different testing techniques and specimen collection methods.

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