SINGAPORE - Infectious disease experts here are urging people to stay home unless they are "100 per cent" well, following news that staff in the coronavirus cluster at PCF Sparkletots Fengshan were at work while sick.

Dr Leong Hoe Nam, who practises at Mount Elizabeth Hospital, told The Straits Times on Thursday (March 26): "If you look at the numbers, we're hitting around 70 cases a day. If we do this consecutively for five days, we'd need a new National Centre for Infectious Diseases to hold the patients. If this goes on, our whole healthcare system will be overloaded.

"So everyone must play their part, no ifs or buts. If you're even a little bit unwell, please don't go out, stay at home. It's high stakes now."

Professor Paul Tambyah, who is from the National University of Singapore Yong Loo Lin School of Medicine's Department of Medicine, agreed.

"Right now when there is a worldwide coronavirus pandemic, it is best to stay home if one does not feel 100 per cent well," he said.

As of 3pm on Thursday, there were 19 people in the PCF Fengshan cluster.

The principal of the pre-school at the centre of the cluster was well when she went to work on March 17 but developed symptoms that afternoon.

On that day, she had a meeting with her employees, and attended a course with other pre-school employees in the evening.

Most of the staff from the centre who tested positive for the virus began developing symptoms from March 20.

The principal's four family members, who do not live with her, also tested positive on March 23 and 24.

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Dr Leong said that on average, people spread the virus to only two to three people. Some, however, will pass the infection to at least five to 10 others.

Citing a recent study on the spread of the coronavirus in Singapore, Prof Tambyah highlighted that 88 per cent of individuals did not transmit the infection to anyone even if they were not in quarantine.

However, three or four patients would later become the source for some major clusters.

He said: "The vast majority of people do not spread (the virus responsible for Covid-19) to anyone. On the other hand, a few individuals become the index patients for large numbers of secondary and tertiary cases."

Both Prof Tambyah and Dr Leong emphasised that it is better to refer to a "super-spreading event" rather than a "super-spreader".

The term "super-spreader" pins a lot of responsibility and blame on a single individual, while in reality, there may be other factors at play, they said.

Prof Tambyah said: "We think that these (super-spreading events) are due to a combination of circumstances and people, and not just people."

Dr Leong said: "Nobody wants to be a super-spreader, nobody chooses to be one. We describe the event, we describe the science, but we don't describe the person."

He added: "We shouldn't pin and judge people with retrospective vision. If anyone knew what would happen after a particular action was taken, if they knew it would lead to a spread, they wouldn't have taken it... we shouldn't nail anyone to a cross retrospectively."

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With that said, there are several lessons to be learnt from the PCF cluster.

Noting that the principal developed symptoms only in the afternoon, he said workplaces should practise temperature-taking thrice a day.

Referring to the meeting that the principal attended, he added: "It's a good reminder that we ought not to meet if possible.

"If you have to meet, an open-air environment is preferred to an air-conditioned one."

Those in a meeting room should maintain a 1m to 2m distance from each other, and should declare if they are feeling unwell before joining the meeting. They should also not share food or drink, which some people do during meetings.

"Ideally, of course, don't have meetings. But if you really have to meet... (take these precautions) and then come out as quickly as possible," he said.

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