Coronavirus: Singapore

Unlinked cases less relevant when S'pore treats Covid-19 as endemic

Time and effort poured into linking cases can be better spent elsewhere, say experts

Resources poured into uncovering how Covid-19 patients are linked to one another could be better channelled towards fighting the virus in other ways, as Singapore moves towards treating the disease as endemic, experts told The Straits Times.

Public health and infectious disease experts said that it now makes less sense to differentiate between linked and unlinked cases.

This followed the Ministry of Health's (MOH) announcement on Wednesday that it would stop disclosing the number of cases with no known connections.

Linking cases helps the authorities know which disease clusters are likely to become "explosive", Professor Paul Tambyah, president of the Asia-Pacific Society of Clinical Microbiology and Infection, said yesterday.

But if Singapore accepts that the coronavirus is "well and truly endemic" - just like diseases such as dengue or tuberculosis - this number becomes less relevant.

He pointed out that the country does not distinguish between linked and unlinked cases for other endemic diseases, although it does track clusters - especially among vulnerable groups. "When we stop linking cases, perhaps we accept that the virus is everywhere and we can loosen up some restrictions," Prof Tambyah said.

Since the start of the pandemic, the number of unlinked Covid-19 cases has been a metric to watch.

Among other things, it suggested "hidden reservoirs" of virus in the community, which could seed new infection clusters.

It is also far more difficult to trace the links between cases now that vaccination rates are high, added Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health.

Vaccinated people are more likely to have mild or asymptomatic infections which may slip under the radar, since individuals may not know they are sick.

As such cases go unreported, scientists will not be able to find the connections between cases.

Elaborating, Professor Dale Fisher, a senior consultant in the National University Hospital's infectious diseases division, said: "There can be several generations of asymptomatic spread and then that chain is identified on the other side of the island.

"So unlinked cases are more expected and we would not need to increase community restrictions."

Temasek chief executive Ho Ching also pointed out that it is still important for MOH to publish data that could give Singaporeans a sense of how many "hidden nodes" of the virus remain in the community. This includes the number of cases picked up through rostered routine testing or even home and workplace self-tests, she said.

In MOH's update on Tuesday, it said the number of unlinked cases in the community had increased to 677 in the past week, up from 184 in the week before. Without the need to connect the dots, the time and effort poured into linking cases can be better spent elsewhere.

At present, Singapore's complex, resource-intensive contact tracing process - which can take days for a single case - helps it identify which cases are linked to one another. Unlinked cases are typically reclassified as new connections emerge.

But whether or not cases are linked is likely to have little impact on how they are managed when detected, said Associate Professor Jeremy Lim from the Saw Swee Hock School of Public Health.

"This is a lot of work and if it has marginal impact on actual practice, then the limited resources might be better deployed elsewhere," he said.

This is especially the case as Singapore's Covid-19 numbers rise.

Prof Teo said: "The burden on the contact tracing teams increases, and they may need more time to establish the case linkages between new cases and previously known cases."

He emphasised that contact tracing to identify people who have been exposed to the virus and isolate them as soon as possible is important and still continues.

Instead of the number of unlinked cases, experts suggested Singaporeans should pay attention to data such as the number of people requiring hospitalisation, supplementary oxygen or intensive care.

These give an indicator of the overall Covid-19 situation here and the country's healthcare capacity. Higher numbers mean the system is closer to being overwhelmed, and could result in more deaths.

"We expect this to rise but not by a lot. We now have a raft of treatments for the severely ill and hospital beds should be reserved for this," Prof Fisher pointed out.

Prof Tambyah noted that it is also important to monitor trends in disease incidence and disease clusters - as is done for dengue or influenza - while Prof Lim added that paying attention to the overall case count is also useful.

As patients tend to deteriorate in their second week or later, knowing this week's numbers - along with the number of patients who are elderly or unvaccinated - can give a sense of future demand, he said.

A version of this article appeared in the print edition of The Straits Times on September 10, 2021, with the headline 'Unlinked cases less relevant when S'pore treats Covid-19 as endemic'. Subscribe