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.
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 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).
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 - http://www.who.int/csr/sars/labmethods/en/)
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). - http://www.who.int/csr/sarsareas/2003_05_10/en/
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. http://www.who.int/csr/sarsarchive/2003_05_07a/en/
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).
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. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5218a1.htm
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 - http://www.cdc.gov/ncidod/sars/
WHO SARS page - http://www.who.int/csr/sars/en/
Department of Health Hong Kong - http://www.info.gov.hk/dh/new/index.htm
Ministry of Health Singapore - http://www.gov.sg/moh/sars/index.html
Health Canada - http://www.hc-sc.gc.ca/english/protection/warnings/sars/index.html
SARSwatch - http://www.sarswatch.org/ - a pretty good site, for a non-medical, non-journalist person ...
Wikipedia's SARS page - http://www.wikipedia.org/wiki/Severe_acute_respiratory_syndrome