New community COVID-19 case after 15 days shows virus still 'lurking about' in the community: Experts

SINGAPORE: A new COVID-19 case in the community - after more than a fortnight with no such cases reported - indicates that the virus is still "lurking about".

"Just because we have not seen any reports of cases previously does not mean the coronavirus has been completely eradicated from within Singapore," Dean of Saw Swee Hock School of Public Health Teo Yik Ying told CNA. 

"What is more likely, and as reflected in this situation of having a new community case after a stretch with no reports of community transmission, is that the coronavirus is still lurking about in the community."

Singapore on Thursday (Nov 26) reported its first community COVID-19 case in more than two weeks, a 32-year-old citizen whose infection is currently unlinked.

READ: 5 new COVID-19 cases in Singapore, with first community infection in more than 2 weeks

Experts CNA spoke to said the new community case indicates that the virus is difficult to eradicate, and that there may be pockets of undiscovered asymptomatic or recovered COVID-19 cases in the community. 

"Having detected zero or few cases in the community does not mean the coronavirus is not circulating within the community, it means our surveillance has not been able to pick up any cryptic transmissions, especially since we know asymptomatic infection is possible," said Prof Teo. 

Infectious diseases expert Leong Hoe Nam said the virus will be difficult to eradicate because it spreads like a "Trojan horse" - it can cause asymptomatic disease and spread asymptomatically. 

"People may have the illness and not know about it and yet pass it to others … You invite someone into the house not knowing they have the virus,” he said, adding that places like South Korea and Hong Kong were initially declared virus-free, but are seeing a resurgence in cases now. 

"It goes to show how difficult it is to eradicate the virus. The chief reasons being the ability to shed the virus for a long time, and the ability of the virus to transmit even though the patient is asymptomatic."

In the United States, early cases in Washington state came from asymptomatic or minimally symptomatic transmissions, and it was not until large nursing home clusters formed that the disease was recognised, said President of the Asia Pacific Society of Clinical Microbiology and Infection Paul Tambyah. 

"In Singapore, nursing home staff are screened regularly so hopefully if that is happening, it will be detected before large clusters occur. The more widespread the testing, the less likely we are to be in that scenario."

Even though Singapore went 15 days without a community COVID-19 case, longer than one infection cycle, this also does not mean COVID-19 has been eradicated, experts said. 

"The virus does not respect arbitrary distinctions between 'community' and 'others'," said Dr Tambyah. 

READ: New community COVID-19 case had dinner with 12 family members at Seoul Garden, investigations under way

COVID-19 is more likely to be deemed eradicated when Singapore has gone 28 days, or two incubation periods, without any cases at all, which is the criterion that the Ministry of Health (MOH) uses to close clusters, he added.

"The experience in Shanghai with locally transmitted cases arising out of the airport suggests that as long as infected individuals are coming into the city, there is a risk of ongoing transmission," said Dr Tambyah.

"We are also not sure that there are no locally transmitted cases, the reports tell us that there are no locally transmitted cases detected locally."

On Nov 21, MOH revealed that COVID-19 patients visited Bugis Street and the Kopitiam @ Jurong East while they were still infectious. This suggests that there may have been a locally transmitted case detected overseas, said Dr Tambyah. 

"If all the cases were imported and detected while the visitors or returnees were on SHN at hotels or in homes, then there should not have been people in Bugis or Jurong East potentially exposed unless there was a breach."

THE RISK OF IMPORTED INFECTIONS

Experts CNA spoke to also agreed that it was important to secure imported cases and prevent infections from leaking into the community, similar to how the pandemic began here in February. 

Singapore cannot close its borders completely, and there will be interactions with people from overseas or incoming travellers who are long-term work pass holders or returning Singaporeans, said Prof Teo. 

Thus, there will always be a "very small risk of spillovers" from any infected travellers to the community, as a negative swab test after a 14-day stay-home notice may not completely rule out the chance of an infection developing. 

"I actually do not see the need for Singapore to ever declare that we have successfully eradicated the coronavirus from within Singapore," he added. 

"The reality is that we will never be able to know anyway, especially since we are not conducting repeated mass screening of the entire population - which is hugely inefficient and unnecessary for Singapore."

Singapore has "well-calibrated" border control measures that are adjusted according to assessments of importation risks, said Prof Teo. This, he added, explains why there are different rules depending on where the travellers arrive from, in terms of the duration and location of quarantine, as well as the extent of pre-departure and on-arrival testing. 

"After all, the major outbreaks of COVID-19 in Singapore in late January and mid-March were all started by incoming tourists and returning Singaporeans who have been infected prior to entering Singapore."

MOH’s decision to increase testing availability from Dec 1 will "give us a clearer idea" whether there are actually cases in the community that are not being detected by the current measures, said Dr Tambyah. 

From Dec 1, any company or person who requires a COVID-19 polymerase chain reaction test will be able to get one at approved providers. 

This includes individuals who need pre-departure testing before they travel. Companies can also procure such services from the approved providers.

READ: COVID-19 PCR tests for companies, individuals to be made available from approved providers from Dec 1

"While it is very encouraging to see that there are no locally transmitted cases detected in the last two weeks, it is not possible to fully assess the effectiveness of current methods without knowing how many tests were done in the various sentinel surveillance groups," added Dr Tambyah. 

Despite the low number of community COVID-19 cases, Singapore "cannot let down its guard" and must continue with safe management measures, said Prof Teo. 

The safe management measures are primarily focused on minimising the chance that an infected person will go on and spread COVID-19 to others in the community as a result of any workplace, public or social interactions, he added. 

Large-scale routine testing for certain high-risk segments of the population that interact more with the public or stay in higher density dormitories would be more practical than mass testing of the entire population, said Prof Teo. 

"These measures are tried and tested to be effective, looking at the control of the COVID-19 situation in the community."

"It is prudent to remember that, until the world really gets a handle on COVID-19, Singapore cannot let down its guard and needs to continue with our safe management measures," he added. 

"Otherwise, there is a real risk that Singapore will go down the path of other countries, where the community measures are repeatedly dialled up and down, and sector-specific or even nationwide lockdowns reinstated repeatedly, when the community cases flare up again and again."

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