Lab plays key role in virus fight

June 25, 2020

Testing hub:

Deep throat saliva specimens are sent to the Public Health Laboratory Services Branch in Shek Kip Mei every day for COVID-19 testing.

Accurate results:

Nucleic acid testing is considered the most accurate method to identify COVID-19 to date.

Meeting demand:

Medical Technologist Anita Ng says the number of tests carried out during the peak of the epidemic could reach as many as 4,000 per day.

Approved technology:

Scientific Officer Peter Cheng designed the primers and probes required for the test.

Download Video| Transcript

Voiceover: 
From airport arrivals, public hospitals to private clinics, the Enhanced Laboratory Surveillance Programme was further extended to identify COVID-19 cases early to minimise the risk of community transmission.

Public Health Laboratory Services Branch Medical Technologist Anita Ng:
The first (confirmed) case in Hong Kong was actually (discovered) on my birthday. We diagnosed the first case at around 5pm. Since it was the first case, we had to do a lot of re-testing, ask for another sample and also do other tests to confirm it. 

Voiceover: 
The number of tests carried out can reach as many as 4,000 per day. 

Public Health Laboratory Services Branch Medical Technologist Anita Ng:
People are requesting the test results in a very short period of time. We have to try our very best to finish everything within a day.

Voiceover: 
The tests are not limited to human specimens. 

Public Health Laboratory Services Branch Medical Technologist Anita Ng:
For environmental specimens, we have to test at least 10 times per specimen to ensure it is a true negative.

Voiceover: 
All the specimens end up here.

Public Health Laboratory Services Branch Scientific Officer Peter Cheng: 
We design our own in-house test. Based on what was published in the literature, we can design the primers and probes from the public sequence (data) mainly from China. 

Then we can make use of the primers and probes and put them into use with our own existing instruments and reagents. 

The sensitivity is almost 100%. And the specificity is also (almost) 100%. That means we don't have any problem of false positives or false negatives.  

Voiceover: 
Samples must be collected properly to ensure accurate test results. Patients are advised to collect deep throat saliva samples as soon as they wake up in the morning, before eating, drinking or brushing their teeth to increase the chances of an accurate diagnosis.

Since the first confirmed case of COVID-19 in Hong Kong, the Enhanced Laboratory Surveillance Programme, which provides free COVID-19 testing, has been extended from public hospitals, private clinics and airport arrivals to bus drivers to minimise the risk of community transmission.

Deep throat saliva specimens are sent to the Public Health Laboratory Services Branch in Shek Kip Mei every day for testing.

Medical Technologist Anita Ng recalled that the first confirmed case was discovered on her birthday, making it an exciting but hectic day for her.

“We diagnosed it at around 5pm. Everyone was in a panic. We had to ask for another sample and do a lot of re-testing to confirm it.”

Round-the-clock testing
During the peak of the epidemic in Hong Kong, the number of tests carried out could reach as many as 4,000 per day. The laboratory also deals with urgent testing requests such as for the 1,800 passengers on the World Dream Cruise in February and the Luk Chuen House residents who were evacuated from the Sha Tin housing block earlier this month.

“We had to try our very best to finish everything within a day. We ate for 10 minutes and then continued to test,” Ms Ng added.

The tests are not limited to human specimens. Multiple worshippers at a Buddhist temple in North Point were infected in February, so the Department of Health sent staff to collect environmental specimens from common areas as well as objects such as scriptures and kneeling blankets.

“The number of viruses in environmental specimens is usually low. We have to test at least 10 times per specimen to ensure it is a true negative,” explained Ms Ng.

Self-developed technology
According to Public Health Laboratory Services Branch Scientific Officer Peter Cheng, nucleic acid testing is the most accurate testing method to identify COVID-19 to date.

Upon arrival at the laboratory, the specimens undergo pre-analytical treatment. The technologists then extract the nucleic acid from the specimens and add master mix reagents for polymerase chain reaction (PCR) amplification. Fluorescent signals can be detected during the process for the presence of the virus.

Mr Cheng designed the primers and probes required for the test. The technology was approved by the Hong Kong Laboratory Accreditation Scheme.

“The sensitivity is almost 100%. Even if there are only 200 copies of the virus per millilitre they can be detected. The specificity is also up to 100%. That means we do not have any problem of false positives or false negatives,” he said.

As of June 16, more than 300,000 samples had been tested by the Public Health Laboratory Services Branch and the Hospital Authority.

To advance the identification of COVID-19 infected patients, the Enhanced Laboratory Surveillance Programme was further extended to cover bus drivers last week.