Severe acute respiratory syndrome (SARS)
Charles Gomersall and Gavin Joynt
Note that due to the recent emergence of this condition much of the
information given on this page is based on, as yet, unpublished data collected
in Hong Kong.
This page is updated regularly. Last update January 13th 2004.
A lecture on the ICU management
of SARS is available for download.
Epidemiology
- In 2003 large outbreaks of SARS occurred in
- Mainland China
- Hong Kong
- large proportion of those infected are health care workers and medical
students
- Singapore
- Hanoi
- Taiwan
- Toronto
- In 2004
- four confirmed cases of SARS, unrelated to laboratory exposure, have been
diagnosed in Guangzhou, China
Updated information on epidemiology
Aetiology
- infection with SARS coronavirus (SARS-CoV)
Infection control
- respiratory droplet
- possibly airborne
- faecal droplets
- SARS CoV may be able to survive on inert surfaces for days at 20ºC but
fomite spread is probably not a major route of spread
- early data suggests that the illness is highly, although selectively
contagious:
- evidence of transmission of the disease between patients without very
close contact (eg guests in the same hotel)
- absence of transmission between family members with very close contact
(eg husband and wife sharing a bed)
- reasons for selectivity are unclear
- appear to be super-spreading events where certain patients and certain
times infect a large number of events. Also occurs in other diseases
- infection with SARS CoV is not invariably associated with severe
respiratory disease but asymptomatic
infection probably does not occur or is rare. Similarly transmission
from patients with mild illness is unusual.
- patients thought to remain infectious for up to 10 days after resolution
of fever (but little data
Nosocomial infection
- transmission to healthcare workers, other patients and visitors documented
- increased risk with increased proximity to the patient
- evidence of temporal association between use of nebulizer and infection of
medical students taking clinical examination in close proximity to index
case
Infection control measures in PWH ICU
Click here for details
Clinical features
Suspect SARS in patients with a history of contact with SARS patient or
travel to Far East
Incubation period
- mean 6 days
- range 2-16 days
Prodrome/early phase
- viral replication is probably most active during this phase
- fever (>38°C), which is often high
- may be absent, particularly in the elderly
- ~10% of patients are afebrile throughout their illness
- chills and rigors common
- headache, malaise, or myalgia frequent
- ± mild respiratory symptoms
- ± nausea, vomiting and diarrhoea
- rash, neurologic findings usually absent
Later/Lower respiratory phase
-
usually occurs in second week of illness and may be due to
immunological response to infection
-
clinical and radiological changes consistent with
bronchiolities obliterans organizing pneumonia (BOOP) with acute lung
injury/ARDS
-
dry, non-productive cough
-
dyspnoea
-
± hypoxemia
-
± inspiratory crackles. Wheezing is not a feature of the
syndrome. Auscultation of chest often normal.
-
20-25% require ICU admission, usually with single organ
failure (respiratory)
~90% of those admitted to ICU develop ARDS and ~50% require intubation and ventilation
-
some patients respond to prone ventilation
-
other organ failure, apart from mild cardiovascular failure,
is unusual but gastrointestinal and haematological manifestations are
common.
-
bleeding tendency in some, thrombosis in others
-
38-73% of patients have diarrhoea at some time in
disease
-
does not cause a marked clinically detectable inflammatory
response
Investigations
The diagnosis is less likely if there is no history of exposure and the
patient has one of the following:
- leucocytosis on admission
- lobar consolidation on CXR
- a known pathogen
Treatment
- Broad spectrum antibiotics to cover usual causes of severe community
acquired pneumonia
- Corticosteroids appear to control fever in 1-2 days and improve general
well being. There is no controlled data demonstrating a beneficial effect of
steroids. Use is controversial.
- hydrocortisone 2 mg/kg 6 hourly IV or 4 mg/kg 8 hourly IV. Tail off
over 1 week when there is clear clinical improvement
- severe cases: methylprednisolone 10 mg/kg daily IV for 2 days followed
by hydrocortisone as above
- give repeated doses of methylprednisolone 10 mg/kg or 20
mg/kg daily if fever
or CXR changes persist in the absence of obvious secondary bacterial
infection. Up to a maximum of approximately 5g total dose
- probably should not be used in early phase when active viral
replication is taking place
- significant long term adverse effects eg avascular necrosis of femoral
head
- Ribavirin has been routinely used in Hong Kong but not recommended for use by by Health Canada.
- dose: 8 mg/kg 8 hourly IV for 7-10 days followed by 4mg/kg PO/NG for
another 11-14 days
- adverse effects include:
- haemolytic anaemia. High incidence in Canadian series but higher
doses used
- bone marrow suppression
- contraindicated in pregnancy
- in vitro tests on SARS Co-V suggest that the concentrations
required to inhibit reproduction of the virus are unlikely to be
achieved in vivo
- preliminary data suggest combination with Kaletra may result in better
outcome
- Fluids. Avoid fluid overload and aim for low cardiac filling pressures.
- Low pressure low volume ventilation with permissive hypercapnia using algorithms
based on the ARDSnet
study. Pneumomediastinum (both spontaneous and associated with ventilation) and
pneumothoraces are common
Prognosis
Worse outcome appears to be associated with:
- increasing age
- initial high LDH
- high absolute neutrophil count on presentation
- male sex
- hypoxia
ICU mortality ~25-50%
There are insufficient data to reliably identify prognostic factors in
critically ill patients with SARS but on univariate analysis advanced age, more
severe illness, shorter delay between symptom onset and ICU admission, chronic
disease or immunosuppression, lower steroid dose, higher lymphocyte count,
nosocomial sepsis and positive fluid balance were associated with poor outcome
(click here for details).
Lung function tests 3 months after presentation are suggestive of a
restrictive lung defect but in most the gas transfer factor is normal and in
some cases the changes are explicable on the basis of respiratory muscle
weakness.
Acknowledgement
We would like to thank all the staff of the Prince of Wales Hospital ICU for their
courage and commitment to patient care, particularly in the early stages of the
outbreak when little was known about this disease other than that it was highly
contagious and could cause severe life-threatening illness.
Further reading
World Health Organization. Severe
acute respiratory syndrome
CDC SARS
website
N.
Lee et al. A major outbreak of Severe Acute Respiratory Syndrome in Hong Kong
K.W.
Tsang et al. A Cluster of Cases of Severe Acute Respiratory Syndrome in Hong
Kong
S.M.
Poutanen et al. Identification of Severe Acute Respiratory Syndrome in Canada
J.M.
Drazen. Case Clusters of the Severe Acute Respiratory Syndrome
T.G. Ksiazek
et al. A novel coronavirus associated with Severe Acute Respiratory Syndrome
C. Drosten
et al. Identification of a novel coronavirus in patients with Severe Acute
Respiratory Syndrome
Beijing Medical
University SARS website
Mount Sinai Hospital, Toronto website
R. A. Fowler, et al. Critically
ill patients with severe acute respiratory syndrome. JAMA 290
(3):367-373, 2003.
T. W. K. Lew, et al. Acute respiratory distress syndrome in critically ill patients with
severe acute respiratory syndrome. JAMA 290 (3):374-380, 2003.
C.D. Gomersall, et al. Short term outcome of
critically ill patients with severe acute respiratory syndrome.
© Gavin Joynt & Charles Gomersall March, 2003; April,
2003; May 2003; June 2003; July 2003; September 2003; January 2004
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