In 2003, during the severe acute respiratory syndrome (Sars) epidemic, I was quarantined together with the rest of the staff of the Institute of Mental Health (IMH) after a cluster of 24 patients and six nurses from a couple of wards developed fevers.

The Ministry of Health swooped down and imposed a complete lockdown of the entire hospital and we were all moved to various quarantine facilities, where we would be bused (masked and maintaining our social distancing) to work in IMH in the morning and then back to these facilities, where we would spend the rest of our solitary evening isolated from each other. I reckon I was more fortunate than some of my colleagues, as I was assigned a comfortable enough room in a boutique hotel downtown and the quarantine lasted only a few days. (It wasn't Sars in those wards after all, but a more pedestrian flu outbreak.)

I must have felt fear during that time - after all, the mortality rate of Sars was around 10 per cent (significantly higher than the current coronavirus) - but the passing years have cleansed those memories of that distant pestilence of any fears. For reasons that were not of my own design or effort, the whole experience left me largely unscathed.

But it might not be so for others.

A study of healthcare workers in China found that those who were quarantined for nine days after being exposed to Sars were more likely - when compared with their colleagues who were not quarantined - to report exhaustion, detachment from others, irritability, poor concentration, indecisiveness, deteriorating work performance, a reluctance to work and a desire to leave their job. Other studies have reported lasting psychological problems among healthcare workers, including post-traumatic stress symptoms, depressive symptoms, heightened risk of alcohol abuse and long-lasting "avoidance" behaviour.

The practice of quarantining - which is to separate and restrict the movement of people who have potentially been exposed to a contagious disease in order to protect others - was first recorded in the Book of Leviticus in the Old Testament as a measure to isolate lepers.

The word "quarantine" dates back to the mediaeval period when the Black Death was raging along the Mediterranean in the 14th century. Venice, which was then a major trading port, sought to protect its citizenry by imposing a wait of 40 days for all ships before any passengers or goods could come ashore. This waiting period became known as "quarantinario", from the Italian word for 40.

The period of 40 days was chosen for religious rather than scientific reasons, as there are numerous references to the number 40 in the Bible: The 40 days and 40 nights of rain that caused the great flood as described in the Book of Genesis; the 40 years the Israelites wandered in the wilderness after fleeing from Egypt; Moses fasted for 40 days in the mountain before going down with the Ten Commandments; and Jesus was tempted by the devil for 40 days and nights in the desert.

Psychological impact

People who are quarantined are often frightened to start with and might be resentful and even resistive - after all, this is a measure where the collective interest takes precedence over their individual freedom.

Most would find it an unpleasant experience, having to put up with all the privations of isolation: The loneliness and boredom, the restriction of movement and activities, the anxiety of waiting for an illness to surface and the angst of being separated from loved ones.

What is perhaps less apparent is the possible adverse effect on the mental health of those who have been quarantined.

With the Covid-19 pandemic, where huge swathes of the world's population have been and still are in lockdown - something that the World Economic Forum called "the largest psychological experiment ever" - we have yet to see the full scale and extent of the psychological impact. But we have studies of previous quarantines from which we can glean some insights, learn some lessons and prepare for - or even stave off - a pandemic of a different kind.

People who have been quarantined are prone to developing a wide range of emotional and psychological disturbances - most commonly unstable mood, as well as insomnia, stress, anxiety, anger and emotional exhaustion.

This was reported in a scholarly review that was published in March this year in The Lancet, one of the foremost medical journals. The authors of the review, who are from the Department of Psychological Medicine at King's College London, combed through 24 studies - from 10 countries - related to Sars, Ebola, H1N1 influenza and the Middle East respiratory syndrome.

The study also found that in some people, the effect of being quarantined can be so severe that they developed post-traumatic stress disorder (a mental disorder that is triggered by a terrifying event - either by experiencing it or by witnessing it - and include symptoms such as hyper-vigilance, flashbacks of the traumatic event with severe emotional distress and physical reactions, nightmares and avoidance behaviour) which can last for years and be rather difficult to treat.

But not everyone would develop such psychological problems, though those with a history of mental illness as well as those who suffered financial losses resulting in serious socio-economic distress appeared to be at particular risk.

There are other external factors that have consequential adverse effects on psychological well-being: A long duration of quarantine with the accrued frustration and enervating boredom; the dread of infection; the worry of not having enough daily essentials to last; the financial precarity; and the lack of information during the period of quarantine.

Emerging from a quarantine may not be the end of an ordeal, as some find themselves being shunned by others who continue to treat them with fear and suspicion.

Like the epidemics that brought them about, quarantines are, by their nature, divisive, and if mismanaged can give rise to stereotyping, scapegoating and even xenophobia.

With the quarantining of hundreds of thousands of migrant workers in Singapore, this is something that demands our attention and concern.

There is also no good systematic study on the psychological effects on the elderly - a demographic group which has been identified to be particularly vulnerable to the severe effects of the coronavirus.

This pandemic is happening at a time when there is already a growing trend for the elderly in many developed countries to live on their own.

In Singapore, the proportion of older adults living alone has been increasing since 2000. In the 15 years from 2000, the percentage of Singaporeans 65 years and older living alone grew from 6.6 per cent to 8.9 per cent, and is predicted to increase to 9.2 per cent by 2030.

Until the virus struck, most relied on a social network of family and friends or volunteers to keep connected and engaged, or simply for a routine and structure in their daily lives. Being quarantined and in continued lockdown means an end to all this.

Unlike younger people who are more tech-savvy and can turn to digital technologies such as Skype, FaceTime and the now ubiquitous Zoom to make virtual connections for work and play, some elders may find computers and smartphones daunting. They would probably face problems navigating the Internet - if they have broadband connection at all. A tide of research has shown that social isolation and loneliness can take a serious psychological and physical toll on the elderly. Loneliness also increases vulnerability to disease by raising blood pressure and heart rates, releasing stress hormones, and increasing the risk of depression and dementia.

Moral imperative

Quarantine can be morally controversial, and some may see it as a crude institutionalised public health instrument that takes away personal liberty by coercion and compulsion, where the police and even the army are deployed to ensure compliance.

But with the Covid-19 pandemic which has already taken so many lives - with all the searing images and reports of stacked up coffins in Italy; the repurposing of refrigerated trailers as makeshift emergency mobile morgues in New York; of bodies being stored in an ice rink in Spain; and of the desperate and exhausted healthcare workers - most people would see it as a moral duty to keep their families, friends, colleagues and even strangers from getting sick, and subject themselves to being quarantined for the good of the community if it comes to it.

And there must be some reciprocity. If the community asks individuals to curtail their liberties for the good of others, there is a reciprocal obligation to assist them. This must go beyond providing for their physical needs and safety; beyond providing assurances that they will still be able to support their family; and beyond making that unnatural experience of quarantine as tolerable as possible.

The challenge is to grasp the wide-ranging, substantial and possibly long-term psychological impact and emotional costs on the thousands who have been quarantined and think of how best to measure, monitor and manage this less visible scourge.

Amid all these frantic efforts to flatten the curve, to shore up the healthcare system and to rescue the economy, it is easy to lose track of this - and this would be to our peril.

• Professor Chong Siow Ann, a psychiatrist, is vice-chairman of the medical board for research at the Institute of Mental Health.