SINGAPORE: In a world-first, a research team at Duke-NUS Medical School established a link between two COVID-19 clusters in Singapore via serological testing on two cases, the Ministry of Health (MOH) announced on Tuesday (Feb 25).
The lab tests showed that a couple, cases 83 and 91, were infected with the coronavirus. The couple are linked to the Life Church and Missions Singapore and came into contact with cases 8 and 9, a couple from Wuhan.
Cases 83 and 91 then passed the infection during a Chinese New Year gathering on Jan 25 to Case 66, who works at Grace Assembly of God church and has been determined by MOH to be the primary case in that cluster.
"This meant that cases 83 and 91 likely got infected from case 8 and 9, and went on to pass the infection to case 66 at the Chinese New Year gathering,” the health ministry said.
Cases 83 and 91 had no symptoms at the time of the investigations, the ministry explained.
Records showed that case 91 had gone to Sengkang General Hospital the day after the gathering with symptoms consistent with COVID-19. Case 83 had also been unwell end-January, and repeatedly sought treatment at a GP clinic.
The MOH epidemiology team arranged for cases 83 and 91 to be tested at the National Centre for Infectious Diseases, including the use of serological tests developed by the Duke-NUS team.
Serological tests are tests that look for antibodies in blood samples.
"The test results confirmed they had earlier been infected with COVID-19," MOH said.
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HOW THE TESTS WERE USED
According to MOH, Duke-NUS had cultured the COVID-19 virus in less than a week after Singapore confirmed its first case.
"Using the virus and genetic material derived from the virus, the research team had then rapidly developed several specific lab tests to detect the virus-specific antibodies for contract tracing and other applications," said MOH.
MOH said the lab test currently used to confirm the COVID-19 infection is a molecular test called the Polymerase Chain Reaction (PCR) which detects the the presence of viral generic material in a biological sample obtained from a patient.
The drawback with this test, said MOH, was that it would not work if the patient had recovered and the body's immune system has cleared the virus.
"However, the immune system produces antibodies in response to the infection. The virus specific antibodies will stay with the recovered patient for longer periods of time, which could be at least for several years," said MOH.
Using two different antibody testing platforms (virus neutralisation assay and ELISA assay), the Duke-NUS team proved that cases 83 and 91 were infected with COVID-19 in late January 2020, as they had very high levels of the virus-specific antibodies in the their blood.
"This result was a significant piece of evidence which confirmed the links between the church clusters and the two Wuhan travellers," added MOH.