非典型肺炎特輯 SARS 保謢常識
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General Information on SARS

What is SARS?

Severe Acute Respiratory Syndrome (SARS) is a type of highly contagious pneumonia caused by a previously unknown virus, a so called 'atypical pneumonia". Other causes of "atypical pneumonia" are influenza, Chlamydia, mycoplasma and other viruses.
"Typical" pneumonia is caused by more common organisms such as bacteria like streptococcus.

Case definition of SARS (according to the WHO)

Suspected Case

  1. A person with fever of 38C higher AND
  2. One or more respiratory symptoms ( cough, shortness of breath, difficulty breathing ) AND
  3. Close contact with a person who has been diagnosed with SARS ( in the previous 10 days )

Probable Case

  1. A suspected case according to the above definition plus
  2. X-ray evidence of pneumonia or respiratory distress syndrome OR
  3. Autopsy findings consistent with respiratory distress syndrome without an identifiable cause

Close Contact means

  1. Having cared for or
  2. Having lived with or
  3. Having had direct contact with respiratory secretions and body fluids of a person with SARS

Social Contact means, you have not lived with, cared for or worked closely with a suspected or confirmed case of SARS but you may have had brief social encounters with a suspected or confirmed case of SARS.
This type of encounter is unlikely to be high risk.

HKU criteria of reporting SARS cases

1. "Confirmed" Case: Cases admitted into SARS ward of HA hospitals and reported to HA SARS Registry.*
2. Suspected Case: Cases admitted into suspected SARS case ward of HA hospitals.

* Criteria for reporting to HA SARS Registry (22/4/2003)

  1. Radiographic evidence of infiltrates consistent with pneumonia, and
  2. Fever >38C or history of such at any time in the past 2 days, and
  3. At least 2 of the following :
    1. History of chills in the past 2 days
    2. Cough (new or increased cough) or breathing difficulty
    3. General malaise or myalgia
    4. Known history of exposure

Exclusion criteria
A case should be excluded if an alternative diagnosis can fully explain their illness
 
Exclusion criteria
Does not completely fulfil the above definition but still considered to be highly likely of SARS on clinical judgment
3. Close Contact : To protect the University community from getting infected within the University, we adopt an extra cautious approach in applying this principle to University staff or students :
 
Close contacts are those who have been working in a small confined area with a suspected or confirmed case or who have had prolonged hours of face to face interaction at close distance with the suspected or confirmed case.
 
Social contacts are those who have engaged in relatively brief hours of social contact with a suspected or confirmed case.
 
Remote social contacts are those who have been in the same room as the suspected or confirmed case for brief hours without any social interaction..

Symptoms and Signs of SARS

Symptoms of SARS in order of frequency are

> Fever 38C more (100%) (not so frequent in elderly or immuno compromised patients)
> Chills, rigor or both (73%)  
> Muscle pain (61%)  
> Cough (57%)  
> Headache (56%)  
> Dizziness (43%)  
> Sputum (30%)  
> Sore throat (23%)  
> Running nose (23%)  
> Nausea/vomiting (20%)  
> Diarrhoea (20%) *some outbreaks like Amoy Gardens had a much higher incidence of diarrhoea which may be related to the route of infection.

Chest x-ray in early stages show patchy infiltration "ground glass" appearance which may progress rapidly to diffuse whitening of the lung fields.

Serial x-rays will be done to assess the progress of the disease.

CT scan may show abnormalities in a patient with negative chest x-ray findings but with clinical symptoms of SARS. It is not recommended for initial investigation.

The cause of SARS

The cause of SARS has been identified as a new form of Coronavirus, never seen in humans before. The origin of the virus is unknown but it is postulated it may have come from an animal source.

The genetic sequencing of the virus has been completed by laboratories in Canada, USA and Hong Kong.

This will enable development of more accurate tests, more specific treatment and eventually a vaccine.

Mode of transmission

The SARS virus can be found in respiratory secretions, blood and excretion of SARS patients and may survive for a long duration (up to 24 hrs) in the environment. The mode of transmission is still believed to be by droplet spread through close person to person contact. These droplets travel a distance of about 3 feet from the mouth or nose of an infected person during talking, coughing or sneezing.

The virus can also survive for as long as 24 hours on surfaces like tables, doorknobs, lift buttons etc. Direct contact with secretions from an infected person on these surfaces and subsequent contact with the mucosal surfaces (e.g. nose, mouth, eyes) can transmit the infection.

This highlights the importance of wearing masks as well as frequent hand washing and avoidance of touching the eyes, face etc. after being in public areas.
Distant airborne transmission is not occurring. Recent evidence also indicates that oral-faecal route may be a mode of transmission as increasing numbers of patients also have diarrhoea as a presenting symptom. Therefore attention should be given to correct preparation, cooking and storage of food and communal sharing of food should be avoided as much as possible.

Incubation period

From experience in Hong Kong, the incubation period appears to be between 2 to 10 days with average presentation occurring between 4 to 6 days.

This is why the isolation period of those close contacts is 10 days to cover the possibility of the longest incubation period.

Diagnostic tests

Laboratory tests currently under development

1. Antibody tests (test on serum)
ELISA (Enzyme Linked ImmunoSorbant Assay) detects antibodies in the serum of SARS patients. Rising titre of IgG can be detected between Day 10-Day 21 after the onset of clinical symptoms and signs.
 
These are reliable tests but are not useful for early diagnosis.
 
2. Molecular tests (PCR) (test on nasopharyngeal aspirates)
PCR can detect genetic material of the SARS virus in various specimens (blood, stool, respiratory secretions or body tissue). Existing PCR tests are very specific but lack sensitivity (i.e. high rate of false negatives) This means that negative tests can't rule out the presence of the SARS virus in patients. Various network laboratories are working on their PCR protocols and primers to improve their reliability.
 
All these tests are only available to patients in hospitals.

Treatments available and outcomes of treatment

Doctors in Hong Kong and Canada are using the antiviral drug Ribavirin + steroid with varying degrees of success. Tests in the USA show no effect of Ribavirin on coronavirus in the laboratory but clinical experience in Hong Kong suggests it is effective in some patients.

New drugs are actively being tested now and we await any news of this development.
In USA only supportive treatments are given to patients but no specific drugs have been given. Analysis and outcomes of treatment will have to be provided by the clinicians treating SARS patients. This information is not available in detail yet.

Mortality rate

Mortality may vary from region to region depending on the level of medical care available to patients. In Hong Kong, the mortality rate cannot be accurately assessed yet because this epidemic is still evolving. Unfortunately, the mortality rate is still increasing. There are two different ways to compute the mortality rate - this can be based on all SARS patients or only based on the patients with a known outcome, i.e. being discharged. Based on numbers on April 27 - the mortality rate is 8.9% and 16.3% for the two methods respectively. The true value lies somewhere between these two figures.

Many of these patients who have died are elderly, had other chronic illnesses, sought treatment at relatively late stage of illness or had an unusually severe form of SARS.

References:

  1. Hospital Authority (HA Information on Management of SARS)
  2. World Health Organisation
  3. Clinical Trials Centre, Faculty of Medicine, the University of Hong Kong