A staff meeting at a church in Tanglin. A Sunday service at another church in Paya Lebar more than a week earlier. A Chinese New Year gathering at Mei Hwan Drive in Serangoon.
Three seemingly unrelated events that bore no apparent link to the Coronavirus Disease 2019 (COVID-19) cases here, much less to each other.
But with expert contact tracing by the Ministry of Health (MOH) and the Singapore Police Force (SPF), coupled with a world’s first laboratory test, the mystery link between one of the largest COVID-19 cluster here and travellers from Wuhan was finally found.
Case 66 – the primary case at Grace Assembly of God
Case 66, a 28 year-old Singaporean male with no travel history to China, works at the Grace Assembly of God as a church staff.
He had reported the onset of symptoms on 29 January – the earliest in the cluster – and had gone to work at the church's Tanglin branch while symptomatic.
Sixteen members and staff of the church were subsequently infected with the virus – initially through a staff meeting he attended, and subsequently through various church activities.
Through detailed epidemiological investigation and assistance from the SPF, MOH determined that Case 66 was the primary case of the cluster at Grace Assembly of God.
But how did Case 66 first contract the virus?
CNY gathering at Mei Hwan Drive
On 12 February, Case 66 was referred to the National Centre for Infectious Diseases (NCID). He was confirmed to have COVID-19 infection two days later.
Upon further investigation, MOH found that he had attended a Chinese New Year (CNY) gathering at Mei Hwan Drive on the first day of CNY, 25 January.
Among the attendees were Cases 83 and 91, a married couple.
When contacted by the contact tracing team, both Cases 83 and 91 were, however, not sick; they had no symptoms of COVID-19.
Cases 83 and 91 – the missing link
Checking through their records, MOH found that Case 91 had actually gone to Sengkang General Hospital’s emergency department on 26 January with COVID-19-like symptoms. Based on the case definitions at that time, she was not identified as a suspect case.
Her husband, Case 83, had also been unwell in end-January, and had sought treatment several times at a general practitioner clinic.
MOH’s investigations had also earlier uncovered that both Cases 83 and 91 were at The Life Church and Missions Singapore on 19 January – the same day Cases 8 and 9, two Chinese nationals from Wuhan, had visited the church.
MOH were now presented with a possible link between Wuhan (Cases 8 and 9), The Life Church and Missions Singapore cluster (through Cases 83 and 91), and the Grace Assembly of God cluster (through Case 66).
Cases 83 and 91 likely got infected from Cases 8 and 9, and had then passed the infection to Case 66 at the CNY gathering, who subsequently passed to his colleagues at Grace Assembly of God.
Establishing a positive link despite COVID-19 negative
MOH arranged for Cases 83 and 91 to be tested at NCID. However, as both were already well, the current test to confirm COVID-19 infection would not work.
This is because the lab test, called Polymerase Chain Reaction (PCR), detects whether viral genetic material (COVID-19 in this case) is present in a patient’s biological sample. When a patient has recovered and his immune system cleared of the virus, the test would return negative.
However, knowing that the immune system produces antibodies in response to the infection – which can stay with the recovered patient for several years – MOH decided to test them with a new type of test, known as the serological test.
Serological testing – a world’s first
In came the research team at Duke-NUS Medical School, who had earlier successfully cultured the COVID-19 virus shortly after Singapore confirmed its first case. The team had then rapidly developed several laboratory tests to detect the virus-specific antibodies for contact tracing, among other applications.
Using two different antibody testing platforms (virus neutralisation assay and ELISA assay), they were able to confirm that Cases 83 and 91 had high levels of antibodies that were specific to COVID-19.
This meant that both cases had indeed been infected with COVID-19 in late-January, even though they had since recovered.
This was a significant piece of evidence, as it definitively established the links between the two church clusters, the CNY family gathering, and the travellers from Wuhan.
Close collaboration between agencies
This significant breakthrough was made possible through the close collaboration between MOH’s contact tracing and epidemiological teams, SPF, as well as the researchers at Duke-NUS Medical School.
MOH and SPF had extensively analysed the activity maps of the confirmed cases, interviewed them as well as their close contacts, in order to establish a detailed map of possible transmission across the different cases.
Duke-NUS researchers’ quick response then provided the confirmation needed to connect the clusters together.
With the discovery of the links between the two church clusters to the travellers from Wuhan, MOH has now determined the likely source of infection for a large majority of the locally-transmitted cases.