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By:
Donald Krogstad, MD and Susan McLellan, MD, MPH&TM
Tulane University Center for Infectious Diseases
Updated April 14th, 2003
An
Adobe Acrobat (.pdf) version of this summary is available by clicking here (240
Kb).
Case
Definition
(Updated, April 14th, 2003.)
(http://www.cdc.gov/ncidod/sars/casedefinition.htm)
Respiratory illness beginning on or after Feb 1st, 2003 with fever (>38o
C) with cough, shortness of breath, or difficulty breathing, plus travel
to affected areas in the Far East or elsewhere within the previous 10
days, including airport transit or close contact with a known SARS case
or a suspect case (this is the CDC definition, which is deliberately
broad). Alternatively, the above plus pneumonia, respiratory distress
syndrome (ARDS) or death is the more stringent WHO definition of a probable
case (http://www.who.int/csr/sars/casedefinition),
which uses the date of November 1st, 2002. Both case definitions
require travel to an affected area or close contact with a suspect or
probable case of SARS.
Worldwide
Overview of the Outbreak (Updated, April 14th, 2003.)
(http://www.who.int/csr/sarscountry)
Major affected areas include China (Hong Kong, Guangdong Province [likely
source of the outbreak], Shanxi), Singapore, Taiwan, Vietnam and Canada
(Toronto). Within China, Beijing has now been added. Countries
with local transmission include Canada, China, Singapore, Taiwan, the
United Kingdom, United States and Vietnam. The estimated case fatality
rates for persons with SARS are 3-5%, occasionally ~8%. Additional clinical
information is available at http://content.nejm.org/.
Domestic
Perspective (Updated, April 14th, 2003.)
(US and Louisiana; http://www.cdc.gov/od/oc/media/sars.htm).
The most recent count of suspected SARS cases in the United States is
166 with no deaths, and there are no suspect cases listed in Louisiana
(http://www.dhh.state.la.us/NEWS/Killerpneumonia03.htm).
Infectiousness (Transmissibility).
Information from Hong Kong. (Updated, April 14th, 2003.)
Physicians in Hong Kong and Toronto have been impressed by the transmissibility
of SARS; the second generation of cases (including the death of a WHO
physician in Hanoi) has been primarily in health care workers, leading
to recommendations for respiratory/other precautions for exposed persons.
However, casual contact has not been associated with transmission. Although
there may also be transmission via environmental routes, such as malfunctioning
sewage/ventilation systems, those concerns are focused in China at the
present time.
Information from
Experience in the United States
(New,
April 14th, 2003.) (http://www.cdc.gov/mmwrpreview/mmwrhtml/mm5214a1.htm).
Of the 166 persons with suspected SARS, 9 (5%) are household contacts
of persons with suspected SARS, 3 (2%) are health care workers (HCWs)
who had been caring for suspected SARS cases, and 154 (93%) had traveled
to one or more affected areas within the previous 10 days. Only
20% of suspected SARS cases in the US have an abnormal chest X-ray or
other pulmonary findings sufficient to satisfy the WHO definition of
SARS.
Interim
Infection Control Guidelines (Updated, April 14th, 2003.) (http://www.cdc.gov/od/oc/media/pressrel/r030329.htm)
The evidence available suggests that the respiratory and contact isolation
procedures already available in hospitals across the United States are
effective in preventing the spread of SARS. There is no need for Level
4 precautions such as “space suits" although first responders,
triage and ER personnel and primary care providers should screen for
potential SARS cases, and should institute appropriate precautions immediately. The information available suggests that SARS
is spread by face-to-face contact (http://www.cdc.gov/od/oc/media/transcripts/t030410.htm).
Potential
Personal Precautions.
At present, respiratory, eye, and contact (gown, glove) precautions
are being recommended by CDC, with recognition that we are early in
the process and additional relevant information will undoubtedly be
available literally within weeks.
Isolation
and/or Quarantine as Control Measures in the United States.
Isolation for up to 10 days after exposure or illness has been recommended
by CDC and WHO. In addition,
President Bush has signed an Executive Order adding SARS to the list
of quarantinable communicable diseases under the Public Health Service
Act, following a briefing by Secretary Thompson, Dr. Julie Gerberding
(Director, CDC) and Dr. Anthony Fauci (Director, NIAID, NIH) (http://www.hhs.gov/news/press/2003pres/20030404a.html).
Travel
Advisories issued by the CDC. (New,
April 14th, 2003.)
CDC has recommended that non-essential travel to mainland China, Hong
Kong, Singapore and Hanoi be cancelled.
There are no recommendations against travel to other affected
countries, such as Canada, the United States, or the United Kingdom
(http://www.cdc.gov/ncidod/sars/travel_advice.htm).
What
should you do if you think you or someone you know may have SARS? (New,
April 14th, 2003.)
The first step is to think logically about potential exposures. If the person involved has not been to an
affected area, has not been exposed to a suspected case, and is not
a health care worker, it is unlikely that they have SARS. The second step (if there is reason to suspect exposure) is to
have that individual evaluated if they fit the relatively liberal suspect
case definition being used in the United States – i.e., Do they have
fever >38o C and respiratory symptoms? If they do (and have had a significant exposure), they should
be evaluated by a primary care provider or other physician who is aware
they are coming and can institute precautions at the time of their arrival
– in case they do have SARS (including a mask for the patient, see above
for recommended precautions). Conversely,
they should not be sent to a crowded emergency room, through the halls
of a busy hospital filled with immunosuppressed patients, or sent to
crowded doctor’s offices without warning (http://www.cdc.gov/ncidod/sars).
This page links to further information regarding
Student Exposure at School, Exposure
Management Guidelines and Healthcare
and Institutional Guidelines.)
Treatment
Strategies that have been used in Hong Kong.
Treatments that have been used in Hong Kong include parenteral ribavirin
and prednisone, as well as serum exchange and plasma exchange. In evaluating
these potentially toxic and heroic strategies, it is well to remember
that they are being used with critically ill patients (often difficult
to ventilate even with positive pressure and 100% O2), among whom one
would expect substantial mortality and that there are no controlled
data on their efficacy (see below for recent information on susceptibility
testing of SARS virus to ribavirin in
vitro).
Short-term
Perspective/ Philosophical Overview on SARS.
How infectious
is SARS? (Updated, April 14th, 2003.)
The evidence available suggests that SARS is transmitted to close
contacts – to physicians, nurses and others caring for persons ill with
SARS, and to immediate family members. Those persons are at risk and
should take precautions (see below). However, there is no evidence for
transmission as the result of casual contact (e.g., sharing an elevator
with someone who is infected). Likewise,
there is no evidence that the simple infection control precautions described
above have failed. Transmission
to close household contacts and health care workers has occurred only
prior to or in the absence of those precautions.
What
should we do to prevent its spread?
Physicians, nurses and other care-givers, including in the home, family
members and close associates of persons with SARS, should wear masks
to protect themselves from droplet respiratory spread. If possible,
patients should also wear masks to protect others in their immediate
environment. In health care settings, masks are recommended with gowns,
gloves and eye protection by CDC at the present time.
What
about isolation or quarantine?
Persons who have been ill with SARS should remain isolated at home for
at least 10 days after they recover. Although President Bush has issued
an executive order adding SARS to the list of quarantinable diseases,
public health officials expect that this will be necessary only in very
unusual situations, if at all, for cases or contacts who refuse to consent
to voluntary isolation.
What
causes SARS? (Updated, April 14th, 2003.)
Current evidence suggests SARS is caused by a coronavirus (similar
to the viruses that cause colds), which is different from the coronaviruses
known previously to infect humans (single stranded RNA enveloped virus,
31 kb). Recent studies in Hong
Kong have identified antibody to this coronavirus in serum specimens
from 35 of 50 patients, with seroconversion or ≥4-fold rises in
titer in paired specimens from 32 subjects. In contrast, no antibodies
were found in 80 controls or 200 blood donors (http://image.thelancet.com/extras/03art3477web.pdf). Reverse transcriptase-PCR amplification of
300 and 405 nt fragments from the polymerase gene suggests that the
agent is a coronavirus which is different (based on nucleotide sequence)
from known coronaviruses (http://content.nejm.org/cgi/content/abstract/NEJMoa030781v1
and http://content.nejm.org/cgi/content/abstract/NEJMoa030747v1).
Is
it caused by a bioterrorist agent?
The current outbreak is thought to have originated in the Chinese province
of Guangdong near Hong Kong; there is no evidence that it was caused
by bioterrorists.
Is
SARS treatable? (Updated,
April 14th, 2003.)
The answer is not yet clear. Although physicians in Hong Kong have used
a specific antiviral drug (ribavirin), there is no evidence yet that
any antiviral is effective (improves the clinical outcome). Note
that studies performed recently at USAMRIID suggest that the coronavirus
isolated from SARS patients is not susceptible to ribavirin in vitro
(http://www.cdc.gov/od/oc/media/transcripts/t030410.htm).
Why
are there so few cases in the US? Why are there more cases in Canada?
The most likely explanation is chance, followed by transmission within
a family group in Toronto (after a trip to the Far East), and then to
their physicians, nurses and other close contacts. These secondary cases
occurred in the absence of contact and airborne precautions. This is
why the CDC and the Immigration Service are providing information to
travelers returning from the Far East.
Why
has SARS spread so much more rapidly in the Far East?
The answer is not yet clear. However, many respiratory diseases spread
more rapidly from person-to-person under conditions of crowding (influenza,
TB, meningococcal infection). Thus, it is possible that more direct
and more prolonged interpersonal contact is a significant factor. Likewise,
more severe disease is typically associated with a greater number of
organisms, and greater infectiousness. (Although there may be genetically-determined
ethnic differences in susceptibility, if such differences exist, they
are not absolute. For example, they did not prevent the death of a WHO
physician from Italy by SARS in Hanoi.)
Why
is the death rate so high in China and Hong Kong (3-5%, possibly 8%)?
One partial explanation is that the CDC case definition used in the
U.S. is more inclusive, i.e., it deliberately includes persons with
milder illness. Conversely, the case definition being used by other
countries and WHO in the Far East requires pneumonia or respiratory
distress. This is potentially analogous to estimating the influenza
case fatality rate by studying only hospitalized cases.
What
will happen next? Where are we now in the process of understanding SARS? (Updated,
April 14th, 2003.)
We are still early in this process, now at a point similar to the second
or third month after the initial outbreak of Legionnaires’ Disease in
Philadelphia. The key first step (identification of the causative
agent) may have already occurred, although it needs to be confirmed
(see below). However, even with this progress, a minimum of months
will be required to identify antimicrobials (antivirals) that are effective,
and likely a year or more to develop an effective and safe vaccine.
What
is necessary to prove that the coronavirus isolated is the cause of
SARS? (New,
April 14th, 2003.)
Two criteria must be fulfilled: 1] The new coronavirus must be isolated from
specimens affected by the disease (e.g., from lung tissue of persons
with SARS pneumonia), and 2] The new coronavirus must produce similar
disease in an animal model and be transmissible from infected, ill animals
to other animals that then become ill.
This would fulfill Koch’s postulates (http://www.cdc.gov/od/oc/media/transcripts/t030410.htm).
What
to do if you think you have SARS.
(Click here for further information.)
Morbid
Mortal Wkly Rep 2003; 52: 241-248.
Morbid
Mortal Wkly Rep 2003; 52:
297-302.
TABLE:
Number and percentage of reported SARS cases, by selected characteristics-United
States 2003. (Click
Here to View Table)
Morbid
Mortal Wkly Rep 2003; 52:
297-302.
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