Severe Acute Respiratory Syndrome or SARS is an emerging infectious disease that causes a type of atypical pneumonia.


The initial outbreak is thought to have begun in the province of Guangzhou in China. From here, the infection is thought to have been brought to Hong Kong by a medical professor who eventually succumbed to the disease. He stayed at the Metropole Hotel in Hong Kong where he ended up infecting multiple people from all around the world, including especially a few people who subsequently brought the infection to Vietnam, Singapore and Canada.

SARS is now thought to be caused by a new, novel (and as yet unnamed) coronavirus that is spread by close contact with someone already infected with SARS.

In late May 2003, studies from samples of wild animals sold as food in the local market in Guangdong, China found that the SARS coronavirus could be isolated from civet cats. This suggests that the SARS virus crossed the species barrier from civet cats; this conclusion is, however, by no means certain as it is certainly possible that the civet cats got the virus from humans and not the other way around or even that the civet cats are a sort of intermediary host. Further investigations are ongoing.,4386,191629,00.html

Spread of SARS

It is currently thought that SARS is spread by fine droplets and is not airborne. This is supported by the fact that, *almost* without exception, healthcare workers employing full barrier nursing and N95 respirator masks while caring for these patients have so far avoided infection.

The incubation period for SARS lasts from 2 to 10 days and is most commonly about 3 days.


Initial symptoms are flu-like, in that there can be any or all of the following symptoms: fever, myalgia, lethargy, gastrointestinal symptoms, cough, sore throat and other non-specific symptoms. The only symptom that is common to all patients appears to be a fever above 38 degrees Centigrade (100.4 degrees Fahrenheit). Later in the disease, susceptible patients will develop shortness of breath.

Physical signs

Physical signs are inconclusive in early patients presenting with SARS. There may be no observable signs at all. Some patients will have tachypnoea or dyspnoea or just plain shortness of breath. Some patients in the early stage have some lung auscultation findings which may be crackles or crepitations in any part of either lung. Later in the progression of the disease, tachypnoea and lethargy become more prominent as the patients become more tired from the effort of breathing.


The chest X-Ray appearance of SARS can vary quite significantly from patient to patient. There is no pathognomonic appearance of SARS but the common thread is that the CXR appears abnormal, usually with patchy infiltrates in any part of the lungs. Patients may initially present with a clear CXR but develop signs of SARS later.

The full blood count picture is one of a slight neutropenia with a relative increase in polymorphs and a relative leucopenia. There is usually a raised LDH (lactate dehydrogenase), a raised CK (creatinine kinase) as well as a raised ESR (erythrocyte sedimentation rate) and CRP (C reactive protein).

Diagnostic tests

With the identification and sequencing of the DNA of the coronavirus supposedly responsible for SARS, several diagnostic test kits have been produced.

Three possible diagnostic tests have emerged as top contenders but each one so far has its own drawbacks. The first, an ELISA (enzyme-linked immunosorbant assay) test detects antibodies to SARS reliably but only 21 days after the onset of symptoms. The second, an immunofluorescence assay, can detect antibodies 10 days after the onset of the disease but is a labour and time intensive test, requiring an immunoflourescence microscope and an experienced operator. The last test is a PCR (polymerase chain reaction) test that can detect genetic material of the SARS virus in specimens ranging from blood, sputum, tissue samples and stools. The PCR tests so far have proven to be very specific but not very sensitive. This means that while a positive PCR test result is strongly indicative that the patient is infected with SARS, a negative test result does not mean that the patient does not have SARS.

The WHO has issued guidelines for using the various laboratory tests available to confirm the diagnosis of SARS (available at -

One current drawback is that there currently is no test that will allow for quick screening of patients on presentation in order to exclude SARS.

Research is ongoing in the development of a better laboratory screening test.


A suspected case of SARS is a patient who has any of the symptoms including a fever of 38 degrees Centigrade or more AND who has either a history of contact with someone with a diagnosis of SARS within the last 10 days OR travel to any of the regions identified by the WHO as areas with recent local transmission of SARS (affected regions as of 10th May, 2003 are parts of China, Hong Kong, Singapore and the province of Ontario, Canada). -

A probable case of SARS has the above findings plus positive chest x-ray findings of atypical pneumonia or respiratory distress syndrome.

With the advent of diagnostic tests for the coronavirus probably responsible for SARS, the WHO has added the category of "laboratory confirmed SARS" for patients who would otherwise fit the above "probable" category who do not (yet) have the chest x-ray changes but do have positive laboratory diagnosis of SARS based on one of the approved tests (ELISA, immunofluorescence or PCR).


Any suspected or probable cases of SARS must be isolated, preferably in negative pressure rooms with full barrier nursing precautions taken for any necessary contact with these patients.

Antibiotics have so far proved to be ineffective. Treatment of SARS so far has been largely supportive with anti-pyretics, supplemental oxygen and ventilatory support as per necessary as the disease progresses.

The use of steroids and the antiviral drug ribavirin were initially anecdotally alleged to be of use in treatment, but there has not been any published scientific evidence supporting this hypothesis. Many clinicians now believe that Ribavarin use had in fact worsened many patient's prognosis.

(May 20th, 2003) There may be some benefit from using steroids and other immune system modulating agents in the treatment of the more acute SARS patients as there is some evidence that part of the more serious damage SARS causes is also due to the body's own immune system overreacting to the virus. Expect to hear about some published research into this area soon.

Researchers are now testing all known antiviral treatments for other diseases including AIDS, hepatitis, influenza and others on the SARS-causing coronavirus to see if any of them has any significant effect.


Mortality by age group as of May 8, 2003 is below 1% for people aged 24 or younger, 6% for those 25 to 44, 15% in those 45 to 64 and more than 50% for those over 65.

The prognosis of patients with SARS varies. There have been deaths from SARS but there also have been many recoveries. About 85% of patients can be expected to recover well. However, a worryingly fraction of the total number of patients (more than 20%) end up requiring ICU (intensive care unit) monitoring. Of those admitted to the ICU, more than half recover.

Many current patients would not have survived without supplemental oxygen and ventilatory support in ICU. If the disease becomes much more widespread to the extent that all the ICU beds are filled, the mortality rate would increase.

One popular misconception is that only the elderly and those with many other medical problems will succumb to SARS. While it is true that the aforementioned groups will tend to suffer more when infected with SARS, there is a group of otherwise healthy young adults with no previous medical history who seem, for reasons unexplained so far, to be more susceptible to SARS. So far there is no obvious way to tell in advance just by looking at someone, taking a good history and examining them whether or not they will end up requiring ICU care or not. There are clues, of course, but these arise as part of the patient's clinical progress and in the interpretation of his/her investigation results.

How to handle a potential SARS case

Anyone with the symptoms including fever of 38 degrees C AND who has either come from a SARS affected area or has been in contact with someone known to or suspected to have SARS should be handled as a suspect case of SARS until proven otherwise.

Full contact precautions including respirator masks should be used with these patients. The patient should also be immediately referred to a suitable tertiary hospital or the designated hospital for SARS (as the case in Singapore).

Super spreaders

Epidemiological tracing of patient contacts has revealed that a subset of SARS patients become "super infectors" or "super spreaders". For reasons yet unknown, these people are far more infectious than others, spreading the infection to far more people than other patients. Amongst Singapore's SARS index cases, only one was a super infector. Most of Singapore's current (as of 24th April 2003) 189 SARS cases can be traced to her.

A good story on the spread of SARS from person to person as told by this report by a Singapore epidemiologist.

From the frontlines in Singapore
SARS has turned out to be quite a worrying disease, not just because of its infectiveness and severity but primarily because it seems to have a predilection for healthcare workers. Here in Singapore, there were three index cases who were travellers returning from Hong Kong's Metropole Hotel.

As a result of the large number of healthcare workers affected, the Ministry of Health in Singapore has taken the so far unprecedented steps of closing down Tan Tock Seng Hospital and invoking the Infectious Diseases Act to impose home quarantine on all close contacts of current SARS patients and suspected SARS cases. Secondary to this, all other hospitals in Singapore have also cancelled all elective surgery and have cancelled all leave for staff - to take on the added burden of patients who would otherwise have been treated at Tan Tock Seng.

Singapore has moved to take yet another unprecedented step in this saga. As of March 26th, 2003, all primary schools, secondary schools and junior colleges in Singapore will be closed until April 6th. This kind of action because of an infectious disease has never been taken before in this country.

It's now March 31st, 2003 and the SARS situation looks increasingly bleak at this point. The infection appears to have been getting out of hand in Hong Kong. Over the weekend there were more than 100 admissions for SARS, roughly half of whom were residents who stayed in one particular apartment block. This suggests that SARS may be more infectious than originally thought.

April 24, 2003 - It's been a while since my last update. Since then, China has come out and admitted that their SARS problem is far larger than they originally admitted to. On March 31, 2003, the worldwide tally for total number of SARS cases was 1622. It's now swollen to 4288, mostly due to China and Hong Kong. The apartment block in Hong Kong mentioned above, Amoy Gardens, is now known worldwide as the residential block where there were more than 300 cases of "probable SARS". The source of infection has been traced to just one man from mainland China who stayed with relatives in the building.

Singapore continues to take unprecedented steps. On April 20, 2003, it closed down Pasir Panjang Wholesale Market, its biggest market for the distribution of fruits and vegetables for 10 days following an outbreak linked to several workers working there. On April 23, 2003, Singapore implemented full thermal image scanning for all travellers leaving Singapore via Changi Airport. It has plans to eventually expand this screening service to encompass all modes of entry and departure from the island state. It was also announced that all students from primary schools to junior colleges would get a thermometer and be required to measure their own temperatures several times a day.

The Singapore Parliament met on April 24, 2003 and subsequently approved plans to amend the Infectious Diseases Act to allow the government to fine violators of home quarantine without charging them in court,to allow electronic tagging of home quarantine offenders and to allow sentencing of repeat offenders to time in prison.

It's now May 12, 2003 and Singapore has not had any new diagnosed cases of SARS since April 27th. If no new cases emerge by this weekend, Singapore will have fulfilled the WHO criteria for removing Singapore from the list of "areas with local transmission of SARS" as it would have been a total of 21 days (two incubation periods plus one day) since the last patient was infected with SARS. Singapore would then join Vietnam as the only other country in the world so far that has been removed from that list.

May 29th, 2003 - The mood in Singapore has improved. It has been nearly 20 days since the last new case was reported in Singapore. SARS has badly affected the Singapore economy, particularly the travel and tourism sector and the country is looking forward to being declared "SARS free" by the WHO. I hope nothing comes up in the next few days...

CDC SARS page -
WHO SARS page -
Department of Health Hong Kong -
Ministry of Health Singapore -
Health Canada -
SARSwatch - - a pretty good site, for a non-medical, non-journalist person ...
Wikipedia's SARS page -

SARS in Toronto, Canada

The Spring 2003 outbreak of SARS in Toronto received international media attention as "Toronto the good" became the most significant nexus of the disease outside of Asia during April 2003. Concern culminated with a World Health Organization advisory against "unnecessary travel" to Toronto on April 23rd, 2003. However, by this point there had been no new SARS cases in more than the 10 day maximum incubation period, and Toronto officials greeted the warning with derision.

A note on the naming of names

The names of most SARS victims in Toronto have not been officially released. In the writeup below you will see only two victims named, Kwan Sui-chu and Tse Chi-kwai. The Tse family agreed to announce these names "so people would know to take action right away, and save lives," said Ms. Tse in an interview with Toronto's Globe and Mail newspaper. Doing so was a brave action by the family in an environment of fear which has seen incidents of discrimination and racial profiling. They are to be commended for their courage.


In February 2003, a lethal, pneumonia-like illness began spreading in China and Hong Kong. By mid February, China had reported 305 cases of "atypical pneumonia" which would later come to be called Severe Acute Respiratory Syndrome, or SARS.

At Hong Kong's Metropole Hotel hotel, at least 7 people, all of whom had stayed on the same floor between February 12th and March 2nd, became infected. A wedding guest who became sick a week before staying at the Metropole is believed to be the source of the infection at the hotel (see alex.tan's writeup above for details).

One of the infected hotel guests was Toronto resident Kwan Sui-chu, 78, who stayed at the Metropole on February 21st. She and her family were visiting Hong Kong for Chinese New Year. The next day, as they checked out, the couple is believed to have stood near the coughing and sneezing infected man outside the hotel's elevators. They travelled home on Continental Airlines, in case anyone is concerned/curious.

Initial outbreak in Toronto

By the time Kwan flew back to Toronto on February 23rd, she was severely ill. She visited her GP with what is now recognized as full SARS presentation. By the time of her visit her GP should have received Health Canada's "atypical pneumonia" bulletin. For whatever reason, Kwan was not diagnosed with "atypical pneumonia", but was given a prescription for general antibiotics and sent home.

Kwan succumbed to the illness March 5th in Toronto. According to rumour, the investigating coroner ruled heart attack. The coroner apparently did not ask about Kwan's recent medical or travel history. If true, this would be a violation of basic investigative procedure. In any case, SARS was not yet diagnosed or suspected, and the grieving family did not suspect their danger.

Soon after the funeral, several members of the Tse family fell ill. Kwan's 44-year-old son Tse Chi-kwai, became seriously ill and went to Toronto's Scarborough Grace hospital on Saturday, March 8th.

At this point Toronto began to reap the whirlwind of ex-premier Mike Harris' "Common Sense Revolution". Due to severe cutbacks in Ontario's health care system1, there was no diagnostic bed for Tse, and no staff to examine him. He spent an extended time (reportedly about 6 hours, which is quite possible in Toronto) on a gurney in a hallway of Scarborough Grace, waiting for a room. All the while he was fully presenting, coughing and sneezing on the many passers-by. Eventually Tse was placed in an observation room with an elderly man who had been admitted with a racing heart. Tse was probably "at the height of his disease" when the two men shared the room.

When Tse was finally examined, the doctor suspected tuberculosis and advised the family to start wearing masks and avoid visitors, which they did. A nurse at Scarborough Grace Hospital who could read Chinese had noticed the stories about "atypical pneumonia" in the Chinese press and altered the doctor on Monday, March 10th. He alerted Ontario Health authorities, who in turn contacted the World Health Organization. The first alert was issued on March 12th, the same day that Tse died of SARS.

Belatedly, Ontario's health care system began to become alarmed. Toronto Public Health and Health Canada appealed to Canadians to seek medical help if they had been in contact with the Kwan and Tse families and were experiencing SARS symptoms as the sudden onset of a high fever, muscle aches, or other flu-like symptoms.

SARS spreads in Toronto's hospital system

Four other family members of the Tse family were in Toronto hospitals, officials admitted. In fact, in what now seems almost like a perverse attempt by fate to maximize the damage, Ms. Tse and her now-widowed sister-in-law were admitted to Mount Sinai Hospital in central Toronto. Her father was sent to Toronto Western Hospital and her younger brother was sent to Sunnybrook Hospital in north-central Toronto. This effectively spread the SARS risk to every major hospital cluster in Toronto's core.

Other members of the family who had not been diagnosed with the disease were told “not to go out for the time being," and to "wait to see if they get any symptoms.” This was the beginning of Toronto's voluntary quarantine program.

Mrs. Tse's husband, a manager at a computer company, did not become ill. He returned briefly to work after his mother-in-law's funeral before he learned about SARS, but no one at his workplace has been infected. (He has since been working at home by phone and e-mail, under voluntary quarantine.)

Meantime, the elderly man with the racing heart condition had recovered and gone home, only to return two days later. He too had contracted SARS. His lungs filled with fluid, and he died on March 21st. Public health officials advised the family that the burial should be private, and that they should not get too close to the body. The transmission vector for SARS was still a mystery. Dressed in white surgical masks (but not N95s) mourners attended the funeral and graveside service. Unknown to all, two of the mourners were also infected.

By March 25th, it was clear that Scarborough Grace had become a locus of infection, with numerous health care workers falling ill with the disease. Scarborough Grace officially closed its doors to new patients and most visitors. Provincial health officials announced the quarantine of about a dozen affected health workers' families. Ontario Health Minister Tony Clement declared SARS a "reportable, communicable and virulent disease". This declaration gave health officials the authority to track infected people and issue legal orders to stop them from engaging in activities that transmit SARS. (Like, say, breathing.)

On March 26th, Ontario declared a public health emergency. Thousands of people were asked to quarantine themselves in their homes, wearing masks and denying visitors. By this date there were 27 probable cases of SARS in Ontario. The next day, Ontario health officials ordered Toronto hospitals closed to all visitors, exempting only those visiting critically ill patients and parents visiting children.

On March 30th, Ontario health officials announced another SARS death, which took place on March 28th. The victim had been transferred from Scarborough Grace to York Central Hospital in Richmond Hill, near Toronto, thus widening the disease's circle of influence. Public health officials recommended that all hospital workers in the Greater Toronto Area be issued protective gear to stop the spread of SARS.

On April 1st, it was announced that SARS had spread to the world-renowned Sick Kids Hospital. The likely source was an infected health care worker. Nurses in particular often work at several Toronto hospitals, partly due to the cutbacks mentioned earlier. A number of children were isolated and not allowed visitors, not even their parents. Only moon-suited medical staff could visit them.

The same day it was revealed that two more people in Toronto have died of SARS, bringing Toronto's SARS death toll to 6. Both victims were patients in their 70s, being treated in hospital for other ailments.

On April 3rd officials confirmed another SARS death, a 57-year old woman who had been exposed at Scarborough Grace. On April 5th they reported another death, at Toronto Western Hospital, a patient who had transferred there from Scarborough Grace, and the next day a death in the east end, at Rouge Valley Health System. The day after a death at St. Joseph's Health Centre implicated all major Toronto hospitals except Princess Margaret (a cancer treatment facility). Three more deaths, all of elderly patients, were reported on April 12th which brought the death toll to 13.

On April 20th, Canada's largest trauma unit, Sunnybrook Hospital, stopped accepting new patients after four health-care workers showed signs of SARS. The hospital also closed other units.

At time of writing, 21 people had died of SARS, almost all of them elderly or ill patients infected from the initial hospital outbreak. A new case has not been reported in 21 days, twice the maximum 10-day incubation period for SARS.

Other SARS fears

Health officials asked anyone who was present at Scarborough's Highland Funeral Home on April 3rd to contact health authorities and to quarantine themselves. It is thought that a person who was infected with SARS attended a funeral that day, possibly infecting others.

On April 9th, Hewlett-Packard sent approximately 200 workers from a Toronto-area office home after an employee exhibiting SARS symptoms ignored health officials' instructions to remain in quarantine. No one at HP is thought to have become infected.

On April 14th, Toronto health officials ordered all 500 members of a Toronto Catholic sect, Bukas-Loob Sa Diyos, into quarantine. Sect members were exposed to the disease at the funeral of a SARS victim.

The same day a health care worker with SARS symptoms rode the GO train from Burlington's Appleby Station, returning the same way on the 15th. Riders of her GO Train were later warned via posted notices to be on the watch for symptoms, but no one seems to have been infected. The warning was lifted on April 28th.

Officials in York Region, north of Toronto, asked anyone who was at the Ward Damiani Funeral Home in Woodbridge on Friday, April 18, and Saturday, April 19, or who attended a funeral mass at St. David Parish in Maple to contact authorities. One person at the funeral was showing symptoms of SARS.

A number of conventions, music concerts, lectures, and other meetings scheduled for Toronto were cancelled because of fears of the diseases. Over 800 bus tours have been cancelled, and hotels are at 30% of capacity, compared to a seasonal average of 70%.

Restaurants, particularly Asian restaurants like the Mandarin Buffet, have been hit hard with low patronage. Mandarin has been running radio and print ads stressing the precautions they have taken, including special SARS policies restricting employee attendance in case of recent travel to Asia, possible SARS contact, or even slight symptoms of the illness. Prime Minister Jean Chretien has made a point of eating in Toronto's Chinatown to show that it is safe. However it may take quite some time for local confidence to be restored, and even longer for the city's tourist trade to recover.

Major League Baseball issued a warning to its teams that players visiting Toronto should avoid contact with fans, public places and most of all hospitals. The first team to visit, the Kansas City Royals, were very gracious and understanding, and did not let the SARS situation or the rabid sports media goad them into any rash statements or actions.

Your correspondent has ridden Toronto's subway each day throughout the crisis. Ridership appears almost normal. Unlike what you might expect from media coverage, only twice have I seen anyone wearing a mask. Once I saw a proper N95, the other was a poorly fitted surgical mask with a drug company logo, which might as well have been a stage prop for all the good it would have done.

SARS fears beyond Toronto

On April 3rd, the SARS virus was exported from Toronto for the first time, travelling to Manila through a nursing aide. (On April 12th the nursing aide was admitted to San Lazaro Hospital in Manila, where she died on April 14th.)

On April 19th, a Toronto man who attended a business conference in Montreal had symptoms, and 450 people from the meeting were under quarantine. This turned out to be a false alarm.

On April 23rd, the World Health Organization issued an advisory against "unnecessary travel" to Toronto. The next day, Toronto officials reacted with anger, notably Toronto mayor Mel Lastman who was featured in an angry, passionate, and largely fact-free rant on CNN.

Celebrities including Elton John, Billy Joel, Lisa Marie Presley and the reincarnated Styx have cancelled shows, as has media blip Kelly Clarkson.

You reap what you sow.

The costs to Toronto and to Ontario in lost revenue, in containment expenses, in lost work time, and most importantly in lives had far exceeded any savings from the health care costs reductions and bed closures of the Common Sense revolution. The costs of the SARS outbreak to the Canadian economy could top $2.1 billion, according to a recent TD Bank report.

It seems right now like the Toronto outbreak is contained, but as long as SARS exists "in the wild" vigilance and containment will continue to be necessary. The first new plague of the 21st century is upon us, and we have learned that half measures will not do to combat it. The costs of SARS will continue for some time.

On April 28th, Toronto mounted a "Let's show the world what they're missing!" campaign to promote local tourism until the travel ban is lifted.

July 2003 update

By mid-July, SARS was considered completely contained world-wide. The death toll in Toronto had reached 41, including two health-care workers who had become infected in hospital. There remained 13 active cases in Toronto-area hospitals, some of whom are health-care workers. At least two are in critical condition and are not expected to survive the disease.

August 2003 update

By mid-August, the death toll in Toronto had reached 44, including a male doctor, Nestor Yanga, and two female nurses who had become infected in hospital. There remain 8 active cases in Toronto-area hospitals, of which three are in critical condition.


  1. See my December 13, 2002 writeup for a personal adventure in Toronto health care.


  • TV and radio news
  • Friends in the know at University Health Network

SARS medicine on its way?

A group of molecular biologists in Germany (working at the universities of Lübeck, Jena and Würzburg) have achieved a scientific breakthrough, which may represent a great stride forward when it comes to finding a feasible remedy for SARS.

The group, consisting of the German-based researchers Kanchan Anand, John Ziebuhr, Parvesh Wadhwani, Jeroen R. Mesters and Rolf Hilgenfeld, has succeeded in building a structural model of an important component of the SARS-causing corona virus – an enzyme called protease.

Agent of subversion

Protease participates in the process that makes it possible for a virus to enter the cells of the victim and dupe the victim’s cells into starting a mass production of new copies of the virus. If you know the precise structure of the protease, then it is possible to devise a molecule that can inactivate it (a protease inhibitor). The discovery of the structure of the protease of the HIV-virus in the mid-1990s soon led to the development of the present HIV-inhibiting medicines.

Minor modifications

The outlook regarding a possible anti-SARS medicine in the foreseeable future looks even brighter. The SARS virus belongs to the group of corona viruses, which also includes the viruses that cause the common cold. The German-based researchers suggest that certain already available rhinovirus 3C protease inhibitors only need slight modifications to suit the task of inhibiting the SARS-virus protease. One such molecule, an agent by the name of AG7088, is already undergoing clinical tests by a pharmaceuticals company.

The results were published on May 13, 2003 on the web version of the Science magazine.


Science website:

NOTE: It is interesting and encouraging to note that front-line science seems to know no national boundaries or gender differences, not even in Europe. The German-based group includes two Indians, it is led by a woman (Kanchan Anand), and part of the work was carried out in former East Germany (Jena).

(The "SARS From Space Theory", reposted by direction of the powers that be into this node...)

In a rather counter-intuitive theory, Professor Chandra Wickramasinghe of the Cardiff Centre for Astrobiology has argued in a letter to the British medical journal The Lancet that the Severe Acute Respiratory Syndrome (SARS) virus originated from space.

As evidence for the plausibility of his theory, he points to an experiment he participated in, in which collection bags were launched into the stratosphere, 41 kilometers above India, and were found to contain microorganisms which he was unable to culture on terra firma.

Dr. Wickramasinghe considers these organisms "highly evolved", and postulates that historical events such as the plague of Athens in the fifth century BC and the influenza epidemic of 1917 may also have originated from space-faring microorganisms.

Professor Wickramasinge explains that this idea is a logical extension of the "panspermia theory" which postulates that the evolution of life began elsewhere in the cosmos, and expanded to other planets via comets.

Other researchers point to the similarity of the SARS coronavirus to other viruses of mundanely Earthly origin, generally finding the theory "farfetched".


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