Feb. 25, 2020 was a pretty exciting day in Singapore.

The Ministry of Health (MOH) announced that it successfully uncovered the connection between the locally transmitted Grace Assembly of God church Covid-19 cluster and two infected Wuhan travellers.

The link, Case 91, is a 58-year-old Singaporean woman who attended a church service at the Life Church and Missions Singapore with her husband, Case 83, on Jan. 19.

Two Wuhan travellers (Singapore's Cases 8 and 9), unknowingly infected with Covid-19, attended the same service on the same day.

The ministry concluded that it was likely that Cases 83 and 91 was infected at that service.

Six days later, Cases 83 and 91 attended a Chinese New Year gathering at Mei Hwan Drive.

Seven people from that gathering were later diagnosed with Covid-19.

One of them, Case 66, subsequently passed the virus to his colleagues at Grace Assembly of God church.

You can see the clusters and how they're connected visually here:

The ministry was able to diagnose her (post-recovery) using a new serological test, which detects antibodies in a person’s blood, produced in response to the viral infection.

How many other "Case 91"s are there?

According to the ministry, Case 91 started having symptoms on Jan. 26.

She sought treatment at a general practitioner (GP) clinic on three different days — Feb. 1, 6, and 10 — and even went to Sengkang General Hospital.

She wasn't at any of these points tested for the virus though.

It's unclear when she recovered, but she was eventually referred to the National Centre for Infectious Diseases (NCID) on Feb. 18 (because contact tracing linked her to Case 66) and eventually tested positive for the virus on Feb. 22.

That was nearly a month from the onset of her symptoms.

According to MOH, Case 91 mostly stayed at her home at Rivervale Drive before she was admitted.

We know for a fact that she (and her husband, also a Covid-19 patient) attended that Chinese New Year gathering, which is what would give rise to the Grace Assembly of God cluster of 23 cases.

Did she have visitors? Did she go anywhere else? Who did she interact with? Who might she have passed the virus to, between Jan. 26, and her unknown recovery date?

How many cases are out there, just like Case 91?

No one really knows.

Majority of infected people have mild symptoms

But the circumstances surrounding Case 91 won't seem that strange if we were to look at other local confirmed cases of Covid-19, a number of whom also sought treatment for mild yet persistent symptoms on multiple occasions over as long as three weeks before they were diagnosed.

Case 48, for instance, reported an onset of symptoms on Feb. 1.

He then sought treatment at three GP clinics from Feb. 2 to Feb. 9.

Case 85 visited the same GP clinic three times and a polyclinic before he was sent to Khoo Teck Puat Hospital.

Case 83 (91's husband) started displaying symptoms on Jan. 28 and visited a GP clinic four times on Feb. 1, 5, 6, and 10.

It was only more than a week after that, on Feb. 18, that he checked himself into the National Centre for Infectious Diseases (NCID).

Presumably, these patients' symptoms at the start of their infection were so mild that GPs opted to send them home instead of the hospitals or NCID.

A World Health Organisation study based on 17,000 Covid-19 patients found that 82 per cent of them had "mild symptoms".

Some 15 per cent had severe symptoms and only 3 per cent had critical symptoms.

And over here, experts at the National University of Singapore's Yong Loo Lin School of Medicine also agreed that most people will experience Covid-19 as a mild illness.

According to professors Paul Tambyah and Jyoti Somani, there are reports of Covid-19 transmission occurring before the onset of symptoms.

Viral shedding (the release of the virus) from the throat and nose is high and occurs early in the infection — way before any symptoms appear.

It is precisely this combination of mildness and infectiousness that makes Covid-19 much more dangerous.

Wait, is Covid-19 more dangerous because it's less lethal?

The fact that Covid-19 is less lethal than other coronaviruses like SARS and MERS presents a unique danger: that of patients who are sick, but not sick enough to be identified as Covid-19 patients.

Singapore's Case 91 is an apt example.

If Covid-19 were to be more severe, however, it would be much easier to identify affected patients, and distinguish them from those who have a regular flu or common cold.

It's difficult to fault Covid-19 patients who think nothing of the mild symptoms they are experiencing, and spread the virus while going about their daily routines.

As explained by National Development Minister Lawrence Wong, co-chair of the multi-ministry task force, in a press conference on Feb. 17:

"A very mild symptom like a cough or a sore throat and the person says 'nothing to this, I've had sore throats before, I've had cough before, doesn't seem like it's anything major.' And that's why they don't think that they are infected, they continue working, they continue going around, and that's how the virus can spread. So there is that risk."

And if you don't know that you're infected, how do you protect the vulnerable people around you such as the elderly, the pregnant, or those with compromised immunity?

Harvard professor estimates most people will be infected

What makes you think you are not infected with Covid-19? Because you don't feel sick? Or because you haven't been to places confirmed cases have visited?

If the infection is asymptomatic in its early stages, how do you tell if the neighbour that you took the lift with today is uninfected?

What makes you so sure that the lady you sat next to on the train doesn't have Covid-19?

The Atlantic put it quite bluntly in its article "You’re Likely to Get the Coronavirus".

Harvard epidemiology professor Marc Lipsitch told the publication that he predicts about 40 to 70 per cent of people around the world will be infected with the SARS-CoV-2 (the virus that causes Covid-19) within the coming year.

It doesn't mean that they will be very sick. "It’s likely that many will have mild disease, or may be asymptomatic,” he said.

In fact, the NCID, upon studying Singapore's Covid-19 patients, also observed that a significant number had mild symptoms in the initial phase of their infection.

And because their symptoms were so mild, many still went out in public even when they were sick, and potentially, infected even more people.

Lipsitch's prediction might not be too far off.

The number of new cases outside of China and Singapore has been rising steadily.

As of March 2, South Korea and Italy have the largest number of reported Covid-19 cases outside of China.

In light of South Korea's rapidly growing Covid-19 outbreak, Singapore implemented a ban on travellers from Daegu and Cheondo.

However, such border controls will not be feasible as an increasing number of countries test for and report Covid-19 infection.

According to Health Minister Gan Kim Yong on Feb. 25:

"We may begin to remove some of these border controls if it becomes apparent that every country is going to have transmission... It’s not possible for us to isolate Singapore from the rest of the world. It’s not just the economies part - human-to-human interaction, country-to-country interaction (make it) not possible."

What might things look like if the outbreak gets more widespread?

The current strategy of containment in Singapore is likely to give way to one of mitigation.

Contact tracing no longer a priority

Currently, contact tracing is a ridiculously comprehensive process that identifies all contacts that a confirmed or suspected Covid-19 patient had over a certain period, usually two weeks.

Pream Raj, an assistant director of the Communicable Diseases Division of the MOH, says that this involves retracing a person's steps, down to minute by minute activities, “with no gaps”.

Even if the proportion of confirmed cases in Singapore population remains on the lower end of Lipsitch's 40 to 70 per cent estimation, it's not difficult to imagine that in the "small world" of Singapore, we might end up with almost the whole country as close contacts of confirmed patients.

As we approach this point, it will become "futile to try to trace every contact", as Prime Minister Lee Hsien Loong outlined in a recent address.

After all, the notion of quarantine would become meaningless if applied to the bulk of a given population.

Quarantine facilities converted to sick people villages

It will no longer be possible to quarantine all close contacts of confirmed patients, if or when the outbreak becomes more widespread.

Instead of being used to quarantine close contacts of confirmed patients, quarantine facilities may start being used to house mild cases.

Dale Fisher, a professor and senior consultant at the National University Hospital's division of infectious diseases, told Mothership that this is already being done in some parts of China.

He added that one benefit of such an arrangement is that the quarantined community would be allowed to mix amongst themselves, since all are already infected.

Mild cases sent home to recover

Another possibility is for mild cases to be sent home to recover.

The approach would be, as PM Lee explained, to "encourage those who only have mild symptoms to see their family GP and rest at home instead of going to the hospital".

To this end, MOH activated 900 Public Health Preparedness Clinics to provide subsidised treatment and five-day medical certificates to patients with respiratory symptoms.

More importantly, MOH also advised patients to return to the same doctor to seek further treatment.

This may be due to the observation that there are several confirmed cases who visited several GPs.

If their symptoms don't improve after five days, these patients will be referred for further medical assessment and tests.

This is already a reality in some parts of South Korea, where hundreds of confirmed Covid-19 patients are waiting at home for hospital beds to become available.

Such an arrangement allows hospitals and healthcare workers to allocate limited resources for the most vulnerable confirmed patients — the elderly, and those with preexisting medical issues.

While it may be inevitable that a large chunk of Singapore's population gets infected eventually, preventing or slowing down its spread will allow our healthcare system to deal with infections at a manageable pace.

Mothership Explains is a series where we dig deep into the important, interesting, and confusing going-ons in our world and try to, well, explain them.

This series aims to provide in-depth, easy-to-understand explanations to keep our readers up to date on not just what is going on in the world, but also the "why's".

Top image by Andrew Koay.